DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING …old.scteng.co.in/documents/cselms.pdf ·...

1

DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING

CS6003 – AD HOC AND SENSOR NETWORKS

FOR IV YEAR / VII SEMESTER CSE STUDENTS

Regulation 2013, Anna University Chennai

UNIT NOTES

UNIT – I to V

PREPARED BY

Dr.M.SAKTHIVEL, ASP& HOD/CSE

Academic Coordinator HOD Dean- Academic PRINCIPAL

2

CREDIT POINT

ANNA UNIVERSITY, CHENNAI

AFFILIATED INSTITUTIONS

Regulation-2013

B.E. COMPUTER SCIENCE AND ENGINEERING

SEMESTER VII

SL.

No.

COURSE

CODE COURSE TITLE L T P C

THEORY

1. CS6701 Cryptography and Network Security 3 0 0 3

2. CS6702 Graph Theory and Applications 3 0 0 3

3. CS6703 Grid and Cloud Computing 3 0 0 3

4. CS6704 Resource Management Techniques 3 0 0 3

5. CS6003 Ad hoc and Sensor Networks 3 0 0 3

6. IT6006 Data Analytics 3 0 0 3

PRACTICALS

7. CS6711 Security Laboratory 0 0 3 2

8. CS6712 Grid and Cloud Computing Laboratory 0 0 3 2

TOTAL 18 0 6 22

3

SYLLABUS

CS6003 AD HOC AND SENSOR NETWORKS L T P C

3 0 0 3

UNIT I INTRODUCTION 9

Fundamentals of wireless communication technology – the electromagnetic spectrum – radio

propagation mechanisms – characteristics of the wireless channel -mobile ad hoc networks

(MANETS) and wireless sensor networks (WSNs): concepts and architectures. Applications of ad hoc

and sensor networks. Design challenges in ad hoc and sensor networks.

UNIT II MAC PROTOCOLS FOR AD HOC WIRELESS NETWORKS 9

Issues in designing a MAC Protocol- Classification of MAC Protocols- Contention based protocols-

Contention based protocols with Reservation Mechanisms- Contention based protocols with

Scheduling Mechanisms – Multi channel MAC-IEEE 802.11

UNIT III ROUTING PROTOCOLS AND TRANSPORT LAYER IN AD HOC

WIRELESS NETWORKS 9

Issues in designing a routing and Transport Layer protocol for Ad hoc networks- proactive routing,

reactive routing (on-demand), hybrid routing- Classification of Transport Layer solutions-TCP over

Ad hoc wireless Networks.

UNIT IV WIRELESS SENSOR NETWORKS (WSNS) AND MAC PROTOCOLS 9

Single node architecture: hardware and software components of a sensor node - WSN Network

architecture: typical network architectures-data relaying and aggregation strategies -MAC layer

protocols: self-organizing, Hybrid TDMA/FDMA and CSMA based MAC- IEEE 802.15.4.

UNIT V WSN ROUTING, LOCALIZATION & QOS 9

Issues in WSN routing – OLSR- Localization – Indoor and Sensor Network Localization-absolute and

relative localization, triangulation-QOS in WSN-Energy Efficient Design-Synchronization-Transport

Layer issues.

TOTAL:45 PERIODS

4

TEXT BOOK:

1. C. Siva Ram Murthy, and B. S. Manoj, "Ad Hoc Wireless Networks: Architectures and Protocols ",

Prentice Hall Professional Technical Reference, 2008.

.

REFERENCES:

1. Carlos De Morais Cordeiro, Dharma Prakash Agrawal “Ad Hoc & Sensor Networks:

Theory and Applications”, World Scientific Publishing Company, 2006.

2. Feng Zhao and Leonides Guibas, "Wireless Sensor Networks", Elsevier Publication -

2002.

3. Holger Karl and Andreas Willig “Protocols and Architectures for Wireless Sensor

Networks”,Wiley, 2005

5

SENGUNTHAR ENGINEERING COLLEGE -TIRUCHENGODE


LECTURE PLAN

Subject Code : CS6003

Subject Name : AD HOC AND SENSOR NETWORKS

Name of the faculty & Designation : Dr.M.SAKTHIVEL, ASSOCIATE PROFESSOR

Course : VII Semester B.E. –CSE

Academic Year : 2018-2019 (ODD SEMESTER)

Recommended Text books/Reference books

S.No

Title of the book

Author

Reference

1 Ad Hoc And Sensor Networks Dr.M.A.Berlin

Dr.S.Muthusundari T1

2 Ad Hoc Wireless Networks: Architectures

And Protocols

C. Siva Ram Murthy, and

B. S. Manoj T2

3 Ad Hoc & Sensor Networks:

Theory And Applications

Carlos De Morais Cordeiro,

Dharma Prakash Agrawal

R1

4 Wireless Sensor Networks Feng Zhao and Leonides Guibas R2

5 Protocols and Architectures for Wireless

Sensor Networks

Holger Karl and Andreas Willig R3

6

TOPIC REFERENCES TEACHING

AIDS

NO. OF

HOURS

Unit-I Introduction

Fundamentals of Wireless

Communication Technology

T1: 1-2, T2 – Ch1, R1-

Ch1, R1-Ch2 PPT 3

Characteristics of the Wireless Channel

T1: 1-6 T2– Ch2,

R1-Ch3 Black Board 3

Mobile ad hoc networks (MANETS)

and wireless sensor networks (WSNs)

T1 – Ch2, T2-Ch2,

R1-Ch3

Black Board

& PPT 4

Unit-II MAC Protocols For Ad Hoc Wireless Networks

Issues in designing a MAC Protocol

T1:3-2, T2– Ch4,

R1-Ch5, R2-Ch10 PPT 3

Classification of MAC Protocols

T1:3-3, T2 – Ch5,


Multi channel MAC-IEEE 802.11

T1: Ch3-7,T2 – Ch5,


Unit-III Routing Protocols And Transport Layer In Ad Hoc Wireless Networks

Issues in designing a routing and

Transport Layer protocol for Ad hoc

networks

T1:4-2, T2– Ch6, R1-

Ch9, R2-Ch22 Black Board 2

Reactive routing (on-demand)

T1:4-5, T2– Ch7, R1-

Ch11, R2-Ch11 PPT 3

Classification of Transport Layer

solutions

T1:7-3, T2– Ch8,


7

TCP over Ad hoc wireless Networks.

T1:7-4, T2-Ch8,

R2-Ch12 Black Board

3

Unit-IV Wireless Sensor Networks (WSNs) And MAC Protocols

Single node architecture

T1:5-2,T2 – Ch10, R1-

Ch14, R2-Ch28 PPT 3

WSN Network architecture T2– Ch11, R1-Ch15 PPT 3

MAC layer protocols

T1:5-3, T2– Ch11, R1-

Ch15 , R2-Ch28 Black Board 4

Unit-V WSN Routing, Localization & QOS

Issues in WSN routing

T1 :6-1, T2– Ch12,


Indoor and Sensor Network Localization

T1:6-3, T2– Ch13,

R1-Ch15 PPT 3

QOS in WSN

T1:6-4, T2– Ch13,


Energy Efficient Design

T1:6-5, T2– Ch13,


Transport Layer issues

T1:6-7, T2– Ch13,


Total 52 Hrs

Revision 05 Hrs

Total Hours 57 Hrs

8

UNIT I

INTRODUCTION

Fundamentals of Wireless Communication Technology.

The Electromagnetic Spectrum.

Radio Propagation Mechanisms.

Characteristics of the Wireless Channel.

Mobile Ad Hoc Networks (MANETs).

Wireless Sensor Networks (WSNs).

Concepts and Architectures (MANETs and WSNs).

Applications of Ad Hoc and Sensor Networks.

Design Challenges in Ad hoc and Sensor Networks.

9

LIST OF IMPORTANT QUESTIONS

UNIT I - INTRODUCTION

PART- A

1. Define Wireless Communication.

2. What are the types of wireless communications?

3. Mention the advantages disadvantages of Wireless communication.

4. Define Adhoc Networks[May/June’15]

5. Define fading and its types.[May/June’16]

6. Write a short note on Scattering.

7. What do you meant by gossiping?

8. What is the use of directed diffusion?

9. Define Doppler Shift.

10. State Nyquist theorem.

11. Define Co-channel interference.

12. State Shannon's Theorem.

13. What is the use of Data Dissemination in a sensor network?

14. Define Implosion.

15. Differentiate between cellular and adhoc networks.

PART - B

1. Discuss in detail about the issues and challenges in designing a sensor

network.[April/May’15&’16] (OR) What are the Characteristics and features of Adhoc

Networks[Nov/Dec’15]

2. Explain radio propagation mechanisms in detail.

3. Explain the characteristics of the Wireless Channel.[April/May ’15 &’16](OR) How the

path loss and Fading affect in Wireless Channel.[Nov/Dec’15]

4. Explain sensor network architecture.

5. Elaborate the MAC protocols for sensor networks. [April/May’15]

10

PART-A (Questions and Answers)

1. Define Wireless Communication.

Wireless Communication which allows the user to communicate each without requiring any

cables or wires, it uses wireless media links.( Electromagnetic and/or Radio link.)

2. What are the types of wireless communications?

Infrared communication

Cellular systems

Cordless Phones

WLANs

Satellite communication

Bluetooth technology

Wi-Max

3. Mention the advantages disadvantages of Wireless communication.

Advantages:

Self configuring and easy to use

Cost effective

Cheaper to install and maintain

Accessed by anywhere at any time.

Disadvantages:

More vulnerable to attack by unauthorized users

Requiring strong security protocols

Influenced by physical obstructions, Climate conditions and noise interferences etc.,

4. Define Adhoc Networks. [May/June’15]

A wireless ad hoc network (WANET) is a category of wireless network. Wireless Ad hoc

networks are defined as the decentralized type of wireless networks that utilize multi-hop radio

relaying and are capable of operating without the support of any fixed infrastructure (hence they are

also called infrastructureless networks). The absence of any central coordinator or base station

makes the routing a complex one compared to cellular networks.

5. Fading and its types.[May/June’16]

Fading refers the fluctuations in signal strength when they received by the receiver.

Types of Fading:

11

Fast Fading –It refers to the fast fluctuations occurred in amplitude, phase or multipath

delays of the received signal.

Slow Fading- It occurs when the receiver is inside the building and signal is supposed to

pass through building or walls, such obstacles causes little variation in received signal

power.

6. Write a short note on Scattering.

When the wave travels through a medium, which contains many objects with

dimensions small when compared to its wavelength, scattering occurs. The wave gets scattered into

several weaker outgoing signals. In practice, Objects such as street signs, lamp posts, and foliage

cause scattering.

7. What do you meant by gossiping?

Gossiping is a modified version of flooding, where the nodes do not broadcast a

packet, but send it to a randomly selected neighbor. This avoids the problem of implosion, but

it takes a long time for a message to propagate throughout the network.

Though gossiping has considerably lower overhead than flooding, it does not

guarantee that all nodes of the network will receive the message. It relies on the random

neighbor selection to eventually propagate the message throughout the network.

8. What is the use of Directed Diffusion?

The directed diffusion protocol is useful in scenarios where the sensor nodes themselves

generate requests/queries for data sensed by other nodes, instead of all queries arising only from a

BS.

9 . Define Doppler Shift.

The Doppler shift is defined as the change/shift in the frequency of the received signal

when the transmitter and the receiver are mobile with respect to each other. If they are moving

toward each other, then the frequency of the received signal will be higher than that of the

transmitted signal, and if they are moving away from each other, the frequency of the signal at

the receiver will be lower than that at the transmitter. The Doppler shift fd is given by

where v is the relative velocity between the transmitter and receiver, and λ is the wavelength of

the signal.

10. State Nyquist theorem.

12

The Nyquist theorem gives the maximum data rate possible on a channel. If B is the

bandwidth of the channel (in Hz) and L is the number of discrete signal levels/voltage values

used, then the maximum channel capacity C according to the Nyquist theorem is given by

The above a noiseless channel.

11. Define Co-channel interference.

Co-channel interference, sometimes also referred to as narrow-band interference, is due to

other nearby systems (say, AM/FM broadcast) using the same transmission frequency.

12. State Shannon's Theorem.

Noise level in the channel is represented by the SNR. It is the ratio of signal power (S) to

noise power (N), specified in decibels, that is, SNR = 10 log10(S/N).One of the most important

contributions of Shannon was his theorem on the maximum data rate possible on a noisy

channel. According to Shannon's theorem, the maximum data rate C is given by

where B is the bandwidth of the channel (in Hz).

13. What is the use of Data Dissemination in a sensor network?

Data dissemination is the process by which queries or data are routed in the sensor

network. The data collected by sensor nodes has to be communicated to the BS or to any other

node interested in the data.

14. Define Implosion.

Implosion is defined as the situation when duplicate messages are sent to the same

node. This occurs when a node receives copies of the same message from many of neighbors.

15.What is reflection?

When the propagating radio wave hits an object which is very large compared to

its wavelength (such as the surface of the Earth, or tall buildings), the wave gets reflected

by that object. Reflection causes a phase shift of 180 degrees between the incident and

the reflected rays.

13

16.What is diffraction?

When the Propagating radio wave hits an impenetrable object the wave bends at

the edge and thereby causing to propagate in different directions. This effect is called

diffraction.

17. Write the different methods for used for spectrum allocation.

Comparative Bidding Method (Beauty contest)

o Select from the proposals submitted, based on which carrier public would get

benefit.

Lottery System

o Lottery would be held among interested parties

o If party do not have real interest they may resell.

Auctioning method

o Frequency spectrum would be auctioned for highest bidding company.

18.What are the design issues of adhoc wireless network?

o Medium access scheme

o Routing

o Multicasting

o Transport layer protocol

o Pricing scheme

o Quality of service provisioning

o Self-organization

o Security

o Energy management

o Addressing and service discovery

o Scalability

o Deployment considerations

14

19.Differentiate between cellular and adhoc networks. (Nov/Dec 2016)

20. What is MANET? List the characteristics of MANET.

Mobile Adhoc Network (MANET) is a self configuring and decentralized network in

which moving nodes are mobiles. In MANET, each node act as a router and would

communicate with each other via wireless links. The topology would be changed frequently

and forms dynamic topology.

Characteristics of MANET:

Self organizing and adaptive network

Infrastructure less network

Power or energy constraint nodes

Frequent Dynamic topology

Possess variable capacity wireless links

21. What are the applications of Adhoc networks?

Military applications

Emergency services

o Rescue operations

o Disaster relief

o Flooded areas

15

Commercial applications

o Industries

o On line payment

o Shopping malls

Education

o Conferences

o Virtual Class rooms

22. What is the basic concept behind wireless sensor network? List out the sub systems

sensor node.

Wireless Sensor Networks (WSNs) are distributed networks which are formed by small

light weight sensor nodes. Sensor nodes are deployed to monitor the environment or any

objects measuring the physical parameters such as temperature, pressure, humidity, sound and

motion of the object.

Each sensor node consists of three sub systems.

Sensor subsystem

Processing subsystem

Communication subsystem

23. What is LEACH?

LEACH stands for Low-Energy Adaptive Clustering Hierarchy algorithm, it is one

clustering based protocol which minimizes the energy dissipation of the sensor networks. This

algorithm elects the high energy cluster node as the cluster head to communicate with base

station.

24. What do you mean by inter symbol interference?

Inter symbol interference is a distortion in a telecommunication in which one or more

symbols may interfere with other symbols thereby causing unreliable signal.

Distortion in the received signal caused by multipath propagation and consequent

overlapping of individual pulses in the signal will cause blur or mixture of symbols.

16

PART-B (16 Marks Questions and Answers)

1. Explain in detail about Issues and Challenges in Designing a Sensor

Network.[April/May’15&’16] (OR) What are the Characteristics and features of

Adhoc Networks[Nov/Dec’15] [Nov/Dec 2016]

Sensor networks pose certain design challenges due to the following reasons:

Sensor nodes are randomly deployed and hence do not fit into any regular topology. Once

deployed, they usually do not require any human intervention. Hence, the setup and

maintenance of the network should be entirely autonomous.

Sensor networks are infrastructure-less. Therefore, all routing and maintenance

algorithms need to be distributed.

An important bottleneck in the operation of sensor nodes is the available energy. Hence, the

available energy at the nodes should be considered as a major constraint while designing

protocols. For instance, it is desirable to give the user an option to trade off network lifetime

for fault tolerance or accuracy of results.

Hardware design for sensor nodes should also consider energy efficiency as a primary

requirement. The micro-controller, operating system, and application software should be

designed to conserve power.

Sensor nodes should be able to synchronize with each other in a completely distributed

manner, so that TDMA schedules can be imposed and temporal ordering of detected events can

be performed without ambiguity.

A sensor network should also be capable of adapting to changing connectivity due to the

failure of nodes, or new nodes powering up. The routing protocols should be able to

dynamically include or avoid sensor nodes in their paths.

Real-time communication over sensor networks must be supported through provision of

guarantees on maximum delay, minimum bandwidth, or other QoS

parameters. Provisions must be made for secure communication over sensor networks,

especially for military applications which carry sensitive data.

17

2. Explain Radio Propagation Mechanisms In Detail. (Nov/Dec 2016)(April/May 2018)0.

Radio Propagation is the behaviour of radio waves when they are transmitted, or

propagated from one point to another point on the earth. It can be affected by several factors

such as obstacles, noise etc., Radio waves at different frequency propagate in different ways.

Radio waves generally experience the following three propagation mechanisms:

Reflection:

When the propagating radio wave hits an object which is very large compared to its

wavelength, the wave gets reflected by that object. Reflection causes a phase shift of 180

degrees between the incident and the reflected rays.

Diffraction:

This propagation effect is undergone by a wave when it hits an impenetrable object.

The wave bends at the edges of the object, thereby propagating in different directions. This

phenomenon is termed as diffraction.

The dimensions of the object causing diffraction are comparable to the wavelength of

the wave being diffracted. The bending causes the wave to reach places behind the object

which generally cannot be reached by the line-of-sight transmission.

The amount of diffraction is frequency-dependent, with the lower Frequency

waves diffracting more.

Scattering:

When the wave travels through a medium, which contains many objects with

dimensions small when compared to its wavelength, scattering occurs. The wave gets scattered

into several weaker outgoing signals. In practice, objects such as street signs, lamp posts, and

foliage cause scattering. Propagation of radio waves that depict the various propagation

mechanisms that a radio wave encounters.

When the transmitted wave is received at the receiver, the received power of the signal

is generally lower than the power at which it was transmitted. The loss in signal strength, known as

attenuation Propagation mechanisms.

18

Fig:

Propagat

ion

Mechani

sm

3.Explain the characteristics of the Wireless Channel.[April/May ’15 &’16](OR) How the

path loss and Fading affect in Wireless Channel.[Nov/Dec’15]

The wireless channel (transmission medium) is susceptible to a variety of transmission

impediments such as path loss, interference, and blockage. These factors restrict the range, data

rate, and the reliability of the wireless transmission.

The extent to which these factors affect the transmission depends upon the environmental

conditions and the mobility of the transmitter and receiver. Typically, the transmitted signal

has a direct-path component between the transmitter and the receiver.

Other components of the transmitted signal known as multipath components are reflected,

diffracted, and scattered (explained in the previous section) by the environment, and arrive at

the receiver shifted in amplitude, frequency, and phase with respect to the direct path

component.

In what follows, the various characteristics of the wireless channel such as path loss, fading,

interference, and Doppler shift are discussed. Also, two key constraints, Nyquist's and

Shannon's theorems, that govern the ability to transmit information at different data rates, are

presented.

19

Path Loss

Path loss can be expressed as the ratio of the power of the transmitted signal to the

power of the same signal received by the receiver, on a given path. It is a function of the

propagation distance.

Estimation of path loss is very important for designing and deploying wireless

communication networks. Path loss is dependent on a number of factors such as the radio

frequency used and the nature of the terrain.

Free Space model:

The free space propagation model is the simplest path loss model in which there is a direct-

path signal between the transmitter and the receiver, with no atmospheric attenuation or

multipath components.

In this model the relationship between the transmitted power Pt and the received power

Pr is given by

where Gt and Gr are the transmitter and receiver antenna gains,1 respectively, in

the direction from the transmitter to the receiver, d is the distance between the transmitter and

receiver, and λ = c/f is the wavelength of the signal.

Two path model:

Another popular path loss model is the two-ray model or the two-path model. The free

space model described above assumes that there is only one single path from the transmitter to

the receiver. But in reality, the signal reaches the receiver through multiple paths. The two-path

model tries to capture this phenomenon.

The model assumes that the signal reaches the receiver through two paths, one a line-

of sight path, and the other the path through which the reflected wave is received. According to

the two-path model, the received power is given by

20

where Pt is the transmitted power, Gt and Gr represent the antenna gains at the

transmitter and the receiver, respectively, d is the distance between the transmitter and

receiver, and ht and hr are the heights of the transmitter and the receiver, respectively.

Fading

Fading refers to the fluctuations in signal strength when received at the receiver.

Fading can be classified into two types: fast fading/small-scale fading, and slow fading/large-

scale fading.

Fast Fading:

Fast fading refers to the rapid fluctuations in the amplitude, phase, or multipath delays of

the received signal, due to the interference between multiple versions of the same transmitted

signal arriving at the receiver at slightly

different times.

Slow Fading:

Slow fading occurs when objects that partially absorb the transmissions lie between

the transmitter and receiver. Slow fading is so called because the duration of the fade may last

for multiple seconds or minutes. Slow fading may occur when the receiver is inside a building

and the radio wave must pass through the walls of a building, or when the receiver is

temporarily shielded

from the transmitter by a building.

Interference

Wireless transmissions have to counter interference from a wide variety of sources. Two

main forms of interference are adjacent channel interference and co-channel interference.

Adjacent channel interference:

In the adjacent channel interference case, signals in nearby frequencies have components

outside their allocated ranges, and these components may interfere with on-going transmissions

in the adjacent frequencies. It can be avoided by carefully introducing guard bands2 between

the allocated frequency ranges.

21

Co-channel interference:

Co-channel interference, sometimes also referred to as narrow-band interference, is due

to other nearby systems using the same transmission frequency. But this effect can be reduced

by multi user detection system, directional antennas and dynamic channel allocation

mechanisms.

Inter Symbol Interference:

Inter symbol interference is a distortion in a telecommunication in which one or more

symbols may interfere with other symbols thereby causing unreliable signal.

Distortion in the received signal caused by multipath propagation and consequent

overlapping of individual pulses in the signal will cause blur or mixture of symbols.

Doppler Shift

The Doppler shift is defined as the change/shift in the frequency of the received

signal when the transmitter and the receiver are mobile with respect to each other.

If they are moving toward each other, then the frequency of the received signal will

be higher than that of the transmitted signal, and if they are moving away from each other, the

frequency of the signal at the receiver will be lower than that at the transmitter. The Doppler

shift fd is given by

fd =v/λ

where v is the relative velocity between the transmitter and receiver, and λ is the

wavelength of the signal.

Transmission Rate Constraints

Two important constraints that determine the maximum rate of data

transmission on a channel are Nyquist's theorem and Shannon's theorem.

Nyquist's Theorem

The signalling speed of a transmitted signal denotes the number of

times per second the signal changes its value/voltage. The number of changes per second is

measured in terms of baud. The baud rate is not the same as the bit rate/data rate of the signal

since each signal value may be used to convey multiple bits.

22

According to Nyquist’s theorem

Shannon's Theorem

Noise level in the channel is represented by the SNR. It is the ratio of signal power

(S) to noise power (N), specified in decibels, that is, SNR = 10 log10(S/N).One of the most

important contributions of Shannon was his theorem on the maximum data rate possible on a

noisy channel. According to Shannon's theorem, the maximum data rate C is given by

4. Explain Sensor Network Architecture.

The design of sensor networks is influenced by factors such as scalability, fault

tolerance, and power consumption. The two basic kinds of sensor network architecture are

layered and clustered.

Layered Architecture

A layered architecture has a single powerful base station (BS), and the layers of

sensor nodes around it correspond to the nodes that have the same hop-count to the BS.

Fig. Layered architecture.

23

Layered architectures have been used with in-building wireless backbones, and in

military sensor-based infrastructure, such as the multi-hop infrastructure network architecture

(MINA) .

In the in-building scenario, the BS acts an an access point to a wired network, and

small nodes form a wireless backbone to provide wireless connectivity. The advantage of a

layered architecture is that each node is involved only in short-distance, low-power

transmissions to nodes of the neighbouring layers.

Unified Network Protocol Framework (UNPF)

UNPF is a set of protocols for complete implementation of a layered

architecture for sensor networks. UNPF integrates three operations in its

protocol structure: network initialization and maintenance, MAC, and routing

protocols.

Network Initialization and Maintenance Protocol

The network initialization protocol organizes the sensor nodes into different layers,

using the broadcast capability of the BS. The BS can reach all nodes in a one-hop

communication over a common control channel. The BS broadcasts its identifier (ID) using a

known CDMA code on the common control channel.

All nodes which hear this broadcast then record the BS ID. They send a beacon signal

with their own IDs at their low default power levels. Those nodes which the BS can hear form

layer one since they are at a single-hop distance from the BS. The BS now broadcasts a control

packet with all layer one node IDs.

All nodes send a beacon signal again. The layer one nodes record the IDs which they

hear, and these form layer two, since they are one hop away from layer one nodes. In the next

round of beacons, the layer one nodes inform the BS of the layer two nodes, which is then

broadcast to the entire network.

In this way, the layered structure is built by successive rounds of beacons and BS

broadcasts. Periodic beaconing updates neighbor information and alters the layer structure if

nodes die out or move out of range.

MAC Protocol

24

Network initialization is carried out on a common control channel. During the data

transmission phase, the distributed TDMA receiver oriented channel

(DTROC) assignment MAC protocol is used.

Each node is assigned a reception channel by the BS, and channel reuse is such that

collisions are avoided. The node schedules transmission slots for all its neighbors and

broadcasts the schedule.

Routing Protocol

Downlink from the BS is by direct broadcast on the control channel. The

layered architecture enables multi-hop data forwarding from the sensor nodes to

the BS. The node to which a packet is to be forwarded is selected considering

the remaining energy of the nodes.

This achieves a higher network lifetime. Existing ad hoc routing protocols can be

simplified for the layered architecture, Simulated annealing algorithm is an optimization

heuristic in which an objective function is evaluated for different values of the independent

variable. A value which provides an inferior objective value is also accepted with a probability,

which is reduced as the algorithm progresses.

Clustered Architecture

A clustered architecture organizes the sensor nodes into clusters, each governed by a

cluster-head. The nodes in each cluster are involved in message exchanges with their

respective cluster-heads, and these heads send messages to a BS, which is usually an access

point connected to a wired network. where any message can reach the BS in at most two hops.

Clustering can be extended to greater depths hierarchically.

25

Clustered architecture.

Clustered architecture is especially useful for sensor networks because of its

inherent suitability for data fusion. The data gathered by all members of the cluster can be

fused at the cluster-head, and only the resulting information needs to be communicated to the

BS.

Sensor networks should be self-organizing, hence the cluster formation and

election of cluster-heads must be an autonomous, distributed process. This is achieved through

network layer protocols such as the low-energy adaptive clustering hierarchy (LEACH)

LEACH is a clustering-based protocol that minimizes energy dissipation in

sensor networks. LEACH randomly selects nodes as cluster-heads and performs periodic re

election, so that the high-energy dissipation experienced by the cluster-heads in

communicating with the BS is spread across all nodes of the network. Each iteration of

selection of cluster-heads is called a round. The operation of LEACH is split into two phases:

set-up and steady.

26

5. Explain MAC Protocols For Sensor Networks.[Nov/Dec’15][April/May’15&’16]

MAC protocols in sensor networks must create a network infrastructure to establish

communication links among the thousands of randomly scattered sensors.

It must also ensure fair and efficient sharing of communication resources among the nodes, so

that the overall lifetime of the network can be maximized.

The challenges posed by sensor network MAC protocols make them distinct from other

wireless based networks.

There are three basic kinds of MAC protocols used in sensor networks

Fixed allocation

Demand-based

Contention-based.

Fixed Allocation

MAC protocols share the common medium through a predetermined assignment. They are

appropriate for sensor networks that continuously monitor and generate deterministic data

traffic, since all nodes which have been allotted the channel can make use of their slot in each

round.

Fixed-allocation protocols provide a bounded delay for each node. However, in the case of

bursty traffic, where the channel requirements of each node may vary over time, a fixed

allocation may lead to inefficient usage of the channel.

Demand Based

MAC protocols are used in such cases, where the channel is allocated according to the demand

of the node.

Contention Based

MAC protocols involve random-access-based contention for the channel when packets need to

be transmitted. They are again suitable for bursty traffic, but there is a possibility of collisions

and no delay guarantees can be provided.

27

Hence, they are not suitable for delay-sensitive or real-time traffic. Self-Organizing MAC for

Sensor Networks and Eavesdrop and Register Self-organizing MAC for sensor (SMACS)

networks and eavesdrops and register (EAR) are two protocols which handle network

initialization and mobility support, respectively.

SMACS is a distributed protocol for network initialization and link-layer organization. In this

protocol, neighbour discovery and channel assignment take place simultaneously in a

completely distributed manner.

A communication link between two nodes consists of a pair of time slots, at a fixed frequency,

which is randomly chosen at the time of establishing the link.

Such an assignment is possible in sensor networks without interference from neigh boring

nodes because the available bandwidth is much larger than the data rate required for a message

transmission between two nodes. Hybrid TDMA/FDMA.

This is a centrally controlled scheme which assumes that nodes communicate directly to a

nearby BS. A pure TDMA scheme minimizes the time for which a node has to be kept on, but

the associated time synchronization costs are very high.

A pure FDMA scheme allots the minimum required bandwidth for each connection. The

hybrid TDMA/FDMA scheme, proposed in, uses an

optimum number of channels, which gives minimum overall power consumption.

This is found to depend on the ratio of power consumption of transmitter to receiver. If the

transmitter consumes more power, a TDMA scheme is favoured, since it can be switched off in

idle slots to save power.

CSMA-Based MAC Protocols

Traditional CSMA-based schemes are more suitable for point-to-point

Stochastically distributed traffic flows. Binary exponential back-off is used to maintain fairness

in the network. An adaptive transmission rate control (ARC) is also used, which balances

originating and route-through traffic in nodes.

28

UNIT II

MAC PROTOCOLS FOR AD HOC WIRELESS NETWORKS

Issues in designing a MAC Protocol

Classification of MAC Protocols

Contention based protocols

Contention based protocols with Reservation Mechanisms

Contention based protocols with Scheduling Mechanisms

Multi channel MAC-IEEE 802.11

29

LIST OF IMPORTANT QUESTIONS

Unit II

MAC PROTOCOLS FOR AD HOC WIRELESS NETWORKS

PART- A

1. State the low power state of 802.15.[May/June’15]

2. Define Bandwidth efficiency.

3. Write a short note on Synchronization.

4. What are the classifications of MAC protocols?[May/June’16]

5. State Synchronous protocol

6. Abbreviate FAMA and a note on it.

7. What is busy tone multiple access?

8. What is usage of negative acknowledgment?

9. Define frame with a diagram and how it is divided in CATA?

10. What is meant collision report phase?

11. Define Asynchronous protocols.

PART - B

1. Explain the issues in designing a MAC protocol for ad hoc wireless

networks[Nov/Dec’15]

2. Explain in detail about the classifications of MAC protocols.

3. Elaborate the contention-based protocols in detail.

4. Explain Contention-Based Protocols With Reservation Mechanisms. .(OR) What are

the advantages or reservation based MAC protocols over contention based

protocols.[April/May’15 & ‘16]

5. Elaborate Multichannel MAC Protocol.

30

UNIT II MAC PROTOCOLS FOR AD HOC WIRELESS NETWORKS

Issues in designing a MAC Protocol- Classification of MAC Protocols- Contention based

protocols-Contention based protocols with Reservation Mechanisms- Contention based protocols

with Scheduling Mechanisms – Multi channel MAC-IEEE 802.11

TWO MARKS:

1. State the low power state of 802.15.[May/June’15]

IEEE 802.15 is a working group of the Institute of Electrical and Electronics Engineers

(IEEE) IEEE 802 standards committee which specifies wireless personal area network (WPAN)

standards. There are 10 major areas of development, not all of which are active.

2. Define Bandwidth efficiency.

Bandwidth efficiency can be defined as the ratio of the bandwidth used for actual data

transmission to the total available bandwidth. The MAC protocol must try to maximize this

bandwidth efficiency

3. Write a short note on Synchronization.

Synchronization is very important for bandwidth (time slot) reservations by nodes.

Exchange of control packets may be required for achieving time synchronization among nodes.

The control packets must not consume too much of network bandwidth.

4. What are the classifications of MAC protocols?

Ad hoc network MAC protocols can be classified into three basic types:

• Contention-based protocols

• Contention-based protocols with reservation mechanisms

• Contention-based protocols with scheduling mechanisms

5. State Synchronous protocol.

Synchronous protocols require time synchronization among all nodes in the network, so

that reservations made by a node are known to other nodes in its neighborhood. Global time

synchronization is generally difficult to achieve.

31

5. Abbreviate FAMA and a note on it.

The floor acquisition multiple access (FAMA) protocols are based on a channel access

discipline which consists of a carrier-sensing operation and a collision-avoidance dialog

between the sender and the intended receiver of a packet. Floor acquisition refers to the process

of gaining control of the channel. At any given point of time, the control of the channel is

assigned to only one node, and this node is guaranteed to transmit one or more data packets to

different destinations without suffering from packet collisions.

6.What is busy tone multiple access?

The busy tone multiple access (BTMA) protocol is one of the earliest protocols

proposed for overcoming the hidden terminal problem faced in wireless environments. The

transmission channel is split into two: a data channel and a control channel. The data channel is

used for data packet transmissions, while the control channel is used to transmit the busy tone

signal.

7. What is usage of negative acknowledgment?

Usage of negative acknowledgments for reservation requests, and control packet

transmissions at the beginning of each slot, for distributing slot reservation information to

senders of broadcast or multicast sessions.

8. Define frame with a diagram and how it is divided in CATA?

Time is divided into equal-sized frames, and each frame consists of S

slots. Each slot is further divided into five minislots.

The first four minislots are used for transmitting control packets and are called control minislots

(CMS1, CMS2, CMS3, and CMS4). The fifth and last minislot, called data minislot (DMS), is meant

for data transmission. The data minislot is much longer than the control minislots as the control

packets are much smaller in size compared to data

packets.

32

9. What is meant collision report phase?

Collision report phase: If a collision is detected by any node during the reservation

request phase, then that node broadcasts a collision report (CR) packet. The corresponding

source nodes, upon receiving the CR packet, take necessary action.

10. Define Asynchronous protocols.

It does not require any global synchronization among nodes in the Network. These

protocols usually use relative time information for effecting reservations.

11. What is BTMA?

BTMA is Busy Tone Multiple Access Protocol, it comprises the following protocols,

Bust Time Multiple Access

Dual Busy Tone Multiple Access Protocol

Receiver initiated Multiple Access Protocol

12. What is DLPS? Distributed Laxity Based Priority Scheduling is a packet scheduling scheme in which

scheduling can be made based on the status of the neighborhood node and the feedback about packet loss received from destination node.

13. How many phases are there in the reservation process of FPRP protocol?

The Five Phase Reservation Protocol is a single channel TDMA based broadcast

scheduling protocol in which nodes are uses the contention scheme for reserving time slots.

Reservation Request (RR) Phase

Collision Report Phase (CR)

Reservation Confirmation (RC) phase

Reservation Acknowledgement (RA) phase

Packing and Elimination (P/E) phase

14. What are the factors are to be considered in contention based MAC protocol for

scheduling?

Delay targets of packets

Laxities of packets

Traffic load at nodes

Remaining battery power at nodes.

33

PART-B (Questions and Answers)

1. Explain the issues in designing a MAC protocol for ad hoc wireless networks.

[Nov/Dec’15]

The following are the main issues that need to be addressed while designing a MAC

protocol for ad hoc wireless networks.

Bandwidth Efficiency

The radio spectrum is limited, the bandwidth available for communication is also very

limited. The MAC protocol must be designed in such a way that the scarce bandwidth

is utilized in an efficient manner.

The control overhead involved must be kept as minimal as possible. Bandwidth

efficiency can be defined as the ratio of the bandwidth used for actual data transmission

to the total available bandwidth. The MAC protocol must try to maximize this

bandwidth efficiency.

Quality of Service Support

Due to the inherent nature of the ad hoc wireless network, where nodes are usually

mobile most of the time, providing quality of service (QoS) support to data sessions in

such networks is very difficult.

Bandwidth reservation made at one point of time may become invalid once the node

moves out of the region where the reservation was made. QoS support is essential for

supporting time-critical traffic sessions such as in military communications.

The MAC protocol for ad hoc wireless networks that are to be used in such real-time

applications must have some kind of a resource reservation mechanism that takes into

consideration the nature of the wireless channel and the mobility of nodes.

Synchronization

34

The MAC protocol must take into consideration the synchronization between nodes in

the network. Synchronization is very important for bandwidth (time slot) reservations

by nodes.

Exchange of control packets may be required for achieving time synchronization

among nodes.The control packets must not consume too much of network bandwidth.

Hidden and Exposed Terminal Problems

The hidden and exposed terminal problems are unique to wireless networks.

The hidden terminal problem refers to the collision of packets at a receiving node due

to the simultaneous transmission of those nodes that are not within the direct

transmission range of the sender, but are within the transmission range of the receiver.

Collision occurs when both nodes transmit packets at the same time without knowing

about the transmission of each other.

Error-Prone Shared Broadcast Channel

Another important factor in the design of a MAC protocol is the broadcast nature of the

radio channel, that is, transmissions made by a node are received by all nodes within its

direct transmission range.

When a node is receiving data, no other node in its neighborhood, apart

from the sender, should transmit.

A node should get access to the shared medium only when its transmissions do not

affect any ongoing session.

Since multiple nodes may contend for the channel simultaneously, the possibility of

packet collisions is quite high in wireless networks.

35

Distributed Nature/Lack of Central Coordination

Ad hoc wireless networks do not have centralized coordinators. In cellular networks,

for example, the base stations act as central coordinating nodes and allocate bandwidth

to the mobile terminals.

But this is not possible in an ad hoc network, where nodes keep moving continuously.

Therefore, nodes must be scheduled in a distributed fashion for gaining access to the

channel.

Mobility of Nodes

This is a very important factor affecting the performance (throughput) of the protocol.

Nodes in an ad hoc wireless network are mobile most of the time.

The bandwidth reservations made or the control information exchanged may end up

being of no use if the node mobility is very high.

36

2. Explain in detail about the classifications of MAC protocols.

MAC protocols for ad hoc wireless networks can be classified into several categories based

on various criteria such as initiation approach, time synchronization, and reservation approaches.

Ad hoc network MAC protocols can be classified into three basic types:

Contention-based protocols

Contention-based protocols with reservation mechanisms

Contention-based protocols with scheduling mechanisms

Contention-Based Protocols

These protocols follow a contention-based channel access policy. A node does not make any

resource reservation a priori. Whenever it receives a packet to be transmitted, it contends with its

neighbor nodes for access to the shared channel.

Contention-based protocols cannot provide QoS guarantees to sessions since nodes are not

guaranteed regular access to the channel.

Random access protocols can be further divided into two types:

Sender-initiated protocols: Packet transmissions are initiated by the sender node

.

Receiver-initiated protocols: The receiver node initiates the contention resolution protocol.

Sender-initiated protocols can be further divided into two types:

Single-channel sender-initiated protocols: In these protocols, the total available bandwidth is

used as it is, without being divided.

A node that wins the contention to the channel can make use of the entire bandwidth.

Multichannel sender-initiated protocols: In multichannel protocols, the available bandwidth is

divided into multiple channels. This enables several nodes to simultaneously transmit data,

each using a separate channel.

Contention-Based Protocols with Reservation Mechanisms

37

Ad hoc wireless networks sometimes may need to support real-time traffic, which requires

QoS guarantees to be provided. In contention-based protocols, nodes are not guaranteed

periodic access to the channel. Hence they cannot support real-time traffic.

In order to support such traffic, certain protocols have mechanisms for reserving bandwidth a

priori.Such protocols can provide QoS support to time-sensitive traffic sessions. These

protocols can be further classified into two types:

Synchronous protocols: Synchronous protocols require time synchronization among all nodes

in the network, so that reservations made by a node are known to other nodes in its

neighborhood. Global time synchronization is generally difficult to achieve.

Asynchronous protocols: They do not require any global synchronization among nodes in the

network. These protocols usually use relative time information for effecting reservations.

Contention-Based Protocols with Scheduling Mechanisms

These protocols focus on packet scheduling at nodes, and also scheduling nodes for access

to the channel. Node scheduling is done in a manner so that all nodes are treated fairly and

no node is starved of bandwidth.

Scheduling-based schemes are also used for enforcing priorities among flows whose

packets are queued at nodes.

3. Elaborate the contention-based protocols in detail. (Nov/Dec 2016)

Contention-based protocols do not have any bandwidth reservation mechanisms. All ready nodes

contend for the channel simultaneously, and the winning node gains access to the channel.

These nodes are not guaranteed bandwidth, these protocols cannot be used for transmitting real-

time traffic, which requires QoS guarantees from the system.

In this section, several contention-based MAC protocols are described in detail.

MACA Protocol

38

The MACA protocol was proposed as an alternative to the traditional carrier sense multiple

access (CSMA) protocols used in wired networks.

In CSMA protocols, the sender first senses the channel for the carrier signal. If the carrier

is present, it retries after a random period of time.

Otherwise, it transmits the packet. CSMA senses the state of the channel only at the

transmitter. This protocol does not overcome the hidden terminal problem.

In a typical ad hoc wireless network, the transmitter and receiver may not be near each

other at all times.

MACAW Protocol

The binary exponential back-off mechanism used in MACA at times starves flows. This

mechanism allocates bandwidth in a fair manner.

Another problem with BEB algorithm is that it adjusts the back-off counter value very

rapidly, both when a node successfully transmits a packet and when a collision is

detected by the node.

The back-off counter is reset to the minimum value after every successful transmission.

In the modified back-off process, this would require a period of contention to be

repeated after each successful transmission in order to build up the back-off timer

values.

To prevent such large variations in the back-off values, a multiplicative increase and linear

decrease (MILD) back-off mechanism is used in MACAW.

39

Floor Acquisition Multiple Access Protocols

The floor acquisition multiple access (FAMA) protocols are based on a channel access

discipline which consists of a carrier-sensing operation and a collision-avoidance dialog between the

sender and the intended receiver of a packet.

Floor acquisition refers to the process of gaining control of the channel. At any given point of

time, the control of the channel is assigned to only one node, and this node is guaranteed to

transmit one or more data packets to different destinations without suffering from packet

collisions.

Carrier-sensing by the sender, followed by the RTS-CTS control packet exchange, enables the

protocol to perform as efficiently as MACA in the presence of hidden terminals, and as

efficiently as CSMA otherwise.

Two FAMA protocol variants are discussed in this section:

RTS-CTS exchange with no carrier sensing,

RTS-CTS exchange with non-persistent carrier-sensing.

The first variant uses the ALOHA protocol for transmitting RTS packets, while the second

variant uses non persistent CSMA for the same purpose.

Busy Tone Multiple Access Protocols

The busy tone multiple access (BTMA) protocol is one of the earliest protocols proposed for

overcoming the hidden terminal problem faced in wireless environments.

40

The transmission channel is split into two: a data channel and a control channel. The data

channel is used for data packet transmissions, while the control channel is used to transmit the

busy tone signal.

When a node is ready for transmission, it senses the channel to check whether the busy tone is

active. If not, it turns on the busy tone signal and starts data transmission; otherwise, it

reschedules the packet for transmission after some random rescheduling delay.

Any other node which senses the carrier on the incoming data channel also transmits the busy

tone signal on the control channel.

MACA-By Invitation

MACA-by invitation (MACA-BI)is a receiver-initiated MAC protocol. It reduces the number

of control packets used in the MACA protocol.

MACA, which is a sender-initiated protocol, uses the three-way handshake mechanism, where

first the RTS and CTS control packets are exchanged, followed by the actual DATA packet

transmission. MACA-BI eliminates the need for the RTS packet.

Media Access with Reduced Handshake

The media access with reduced handshake protocol (MARCH) is a receiver-initiated protocol.

MARCH, unlike MACA-BI, does not require any traffic prediction mechanism. The protocol

exploits the broadcast nature of traffic from unidirectional antennas to reduce the number of

handshakes involved in data transmission.

In MACA, the RTS-CTS control packets exchange takes place before the transmission of every

data packet. But in MARCH, the RTS packet is used only for the first packet of the stream.

From the second packet onward, only the CTS packet is used.

4. Explain Contention-Based Protocols With Reservation Mechanisms. (Nov/Dec 2016)

41

[April/May’15 & ‘16]

Protocols described in this section have certain mechanisms that aid the nodes in effecting

Bandwidth reservations. Though these protocols are contention-based, contention occurs only during

the resource (bandwidth) reservation phase.

Once the bandwidth is reserved, the node gets exclusive access to the reserved bandwidth.

Hence, QoS support can be provided for real-time traffic.

Distributed Packet Reservation Multiple Access Protocol

The distributed packet reservation multiple access protocol (D-PRMA) extends the

earlier centralized packet reservation multiple access (PRMA) scheme into a distributed

scheme that can be used in ad hoc wireless networks.

PRMA was proposed for voice support in a wireless LAN with a base station, where

the base station serves as the fixed entity for the MAC operation. D-PRMA extends this

protocol for providing voice support in ad hoc wireless networks.

D-PRMA is a TDMA-based scheme. The channel is divided into fixed- and equal-sized frames along

the time axis.

Collision Avoidance Time Allocation Protocol

The collision avoidance time allocation protocol (CATA)is based on dynamic topology

dependent transmission scheduling. Nodes contend for and reserve time slots by means of a

distributed reservation and handshake mechanism.

CATA supports broadcast, unicast, and multicast transmissions simultaneously. The operation

of CATA is based on two basic principles:

The receiver(s) of a flow must inform the potential source nodes about the reserved slot on

which it is currently receiving packets. Similarly, the source node must inform the potential

destination node(s) about interferences in the slot.

42

Usage of negative acknowledgments for reservation requests, and control packet transmissions

at the beginning of each slot, for distributing slot reservation information to senders of

broadcast or multicast sessions.

Hop Reservation Multiple Access Protocol

The hop reservation multiple access protocol (HRMA) is a multichannel MAC protocol which

is based on simple half-duplex, very slow frequency-hopping spread spectrum (FHSS) radios.

It uses a reservation and handshake mechanism to enable a pair of communicating nodes to

reserve a frequency hop, thereby guaranteeing collision-free data transmission even in the

presence of hidden terminals.

HRMA can be viewed as a time slot reservation protocol where each time slot is assigned a

separate frequency channel.

Soft Reservation Multiple Access with Priority Assignment

Soft reservation multiple access protocol with priority assignment (SRMA/PA)was developed

with the main objective of supporting integrated services of real-time and non-real-time

applications in ad hoc wireless networks, at the same time maximizing the statistical

multiplexing gain.

Nodes use a collision-avoidance handshake mechanism and a soft reservation mechanism in

order to contend for and effect reservation of time slots. The soft reservation mechanism allows

any urgent node, transmitting packets generated by a real-time application, to take over the

radio resource from another node of a non-real-time application on an on-demand basis.

SRMA/PA is a TDMA-based protocol in which nodes are allocated different time slots so that

the transmissions are collision-free.

Five-Phase Reservation Protocol

The five-phase reservation protocol (FPRP) is a single-channel time division multiple access

(TDMA)-based broadcast scheduling protocol. Nodes use a contention mechanism in order to

43

acquire time slots. The protocol is fully distributed, that is, multiple reservations can be

simultaneously made throughout the network.

No ordering among nodes is followed; nodes need not wait for making time slot reservations.

The slot reservations are made using a five-phase reservation process.

The reservation process is localized; it involves only the nodes located within the two-hop

radius of the node concerned. Because of this, the protocol is insensitive to the network size,

that is, it is scalable. FPRP also ensures that no collisions occur due to the hidden terminal

problem.

MACA with Piggy-Backed Reservation

MACA with piggy-backed reservation (MACA/PR) is a protocol used to provide real-

time traffic support in multi-hop wireless networks. The MAC protocol used is based

on the MACAW protocol, with the provisioning of non-persistent CSMA (as in

FAMA). The main components of MACA/PR are: a MAC protocol, a reservation

protocol, and a QoS routing protocol.

MACA/PR differentiates real-time packets from the best-effort packets. While

providing guaranteed bandwidth support for real-time packets, at the same time it

provides reliable transmission of best-effort packets.

Time is divided into slots. The slots are defined by the reservations made at nodes, and

hence are asynchronous in nature with varying lengths. Each node in the network

maintains a reservation table (RT) that records all the reserved transmit and receive

slots/windows of all nodes within its transmission range.

Real-Time Medium Access Control Protocol

The real-time medium access control protocol (RTMAC) provides a bandwidth

reservation mechanism for supporting real-time traffic in ad hoc wireless networks.

RTMAC consists of two components, a MAC layer protocol and a Q oS routing

protocol.

44

The MAC layer protocol is a real-time extension of the IEEE 802.11 DCF. The QoS

routing protocol is responsible for end-to end reservation and release of bandwidth

resources.

5. Elaborate Multichannel MAC Protocol.

Multichannel MAC Protocol

The multichannel MAC protocol (MMAC) uses multiple channels for data

transmission. There is no dedicated control channel. N channels that have enough

spectral separation between each other are available for data transmission.

Each node maintains a data structure called Preferable Channel List (PCL). The usage

of the channels within the transmission range of the node is maintained in the PCL.

Based on their usage, channels can be classified into three types.

High preference channel (HIGH): The channel has been selected by the current node

and is being used by the node in the current beacon interval (beacon interval

mechanism will be explained later). Since a node has only one transceiver, there can be

only one HIGH channel at a time.

Medium preference channel (MID): A channel which is free and is not being currently

used in the transmission range of the node is said to be a medium preference channel. If

there is no HIGH channel available, a MID channel would get the next preference.

Low preference channel (LOW): Such a channel is already being used in the

transmission range of the node by other neighboring nodes. A counter is associated

with each LOW state channel.

For each LOW state channel, the count of source-destination pairs which have chosen the

channel for data transmission in the current beacon interval is maintained.

Time is divided into beacon intervals and every node is synchronized by periodic

beacon transmissions. So, for every node, the beacon interval starts and ends almost

at the same time.

45

At the start of every beacon interval, there exists a time interval called the ad hoc

traffic indication messages (ATIM) window. This window is used by the nodes to

negotiate for channels for transmission during the current beacon interval.

ATIM messages such as ATIM,ATIM-ACK (ATIM-acknowledgment), and ATIM-

RES (ATIM-reservation) are used for this negotiation.

The exchange of ATIM messages takes place on a particular channel called the default

channel. The default channel is one of the multiple available channels. This channel is used for

sending DATA packets outside the ATIM window, like any other channel.

A node that wants to transmit in the current beacon interval sends an ATIM packet to the

intended destination node.

The ATIM message carries the PCL of the transmitting node. The destination node, upon

receiving the packet, uses the PCL carried on the packet and its own PCL to select a channel. It

includes this channel information in the ATIM-ACK packet it sends to the source node.

The source node, on receiving the ATIM-ACK packet, determines whether it can transmit on

the channel indicated in the ATIM-ACK message. If so, it responds by sending the destination

node an ATIM-RES packet.

The ATIM-ACK and ATIM-RES packets are also used to notify the neighbor nodes of the

receiver and sender nodes, respectively, about the channel that is going to be used for

transmission in the current beacon interval. The nodes that hear these packets update their

PCLs accordingly.

At the end of the ATIM window, the source and destination nodes switch to the agreed-upon

channel and start communicating by exchanging RTS/CTS control packets.

If the source node is not able to use the channel selected by the destination, it cannot transmit

packets to that destination in the current beacon interval. It has to wait for the next beacon

interval for again negotiating channels.

46

The ATIM packets themselves may be lost due to collisions; in order to prevent this, each node

waits for a randomly chosen back-off period (between 0 and CW min) before transmitting the

ATIM packet.

Operation of the MMAC protocol

At the beginning of the beacon interval, source node S1 sends an ATIM message to receiver

R1. Receiver R1 responds by sending an ATIM-ACK packet (ATIM-ACK(1)) carrying the ID

1 of the channel .

Node S1, on receiving this packet, confirms the reservation by sending an ATIM-RES packet

(ATIMRES(1)) for channel 1. The ATIM-ACK(1) packet sent by receiver R1 is also overheard

by node R2.

When node R2 receives an ATIM packet from source S2, it chooses a different channel with

ID 2, and sends the channel information to source S2 through the ATIM-ACK packet

(ATIMACK(2)).

Channel 2 is agreeable to node S2, it responds by sending theATIM-RES(2)packet, and the

reservation gets established. Once the ATIM window finishes, the data transmission (through

RTS-CTS-DATA-ACK packet exchange) between node pairs S1-R1 and S2-R2 takes place on

the corresponding reserved channels, channel 1 and channel 2,respectively.

In this protocol, it is the receiver node that plays a dominant role in channel selection. In case

all channels are in use at the receiver, even then the receiver selects one of the channels.

The actual data packet transmissions are protected by the RTS/CTS control packet exchange,

the nodes transmitting packets on the same channel need to contend for the channel, as in IEEE

802.11 for transmitting packets.

The protocol also employs a power-saving mode. In case a node realizes after the ATIM

window that it is neither going to transmit packets nor going to receive packets, then the node

goes into a power-saving doze mode.

47

Channel selection is done at the receiver in the following manner. The receiver node uses The

PCL on the received ATIM packet and its own PCL for selecting the best possible channel for

communication with the source node.

The channel selection procedure tries to balance the network load on the channels. If a receiver

node R receives an ATIM packet from a source node S, it selects a channel as below.

• If there exists a HIGH state channel in node R's PCL, then that channel is

selected.

• Else if there exists a HIGH state channel in the PCL of node S, then this channel

is selected.

• Else if there exists a common MID state channel in the PCLs of both node S and

node R, then that channel is selected. If many such channels exists, one of them

is selected randomly.

• Else if there exists a channel which is in the MID state at only one of the two

nodes, then that channel is chosen. If many such channels exist, one of them is

selected randomly.

• If all channels in both PCLs are in the LOW state, the counters of the

corresponding channels at nodes S and R are added, and the channel with the

least count is selected. Ties are broken arbitrarily.

MMAC uses simple hardware. It requires only a single transceiver. It does not have any

dedicated control channel. The throughput of MMAC is higher than that of IEEE 802.11 when

the network load is high.

This higher throughput is in spite of the fact that in MMAC only a single transceiver is used at

each node. Unlike other protocols, the packet size in MMAC need not be increased in order to

take advantage of the presence of an increased number of channels.

1


CS6003 – AD HOC AND SENSOR NETWORKS

FOR IV YEAR / VII SEMESTER B.E. CSE STUDENTS

Regulation 2013, Anna University Chennai

UNIT – III, IV & V

Regulation-2013

SEMESTER VII

SL.

No.

COURSE

CODE COURSE TITLE L T P C

THEORY

1. CS6701 Cryptography and Network Security 3 0 0 3

2. CS6702 Graph Theory and Applications 3 0 0 3

3. CS6703 Grid and Cloud Computing 3 0 0 3

4. CS6704 Resource Management Techniques 3 0 0 3

5. CS6003 Ad hoc and Sensor Networks 3 0 0 3

6. IT6006 Data Analytics 3 0 0 3

PRACTICALS

7. CS6711 Security Laboratory 0 0 3 2

8. CS6712 Grid and Cloud Computing Laboratory 0 0 3 2

TOTAL 18 0 6 22

2

UNIT III

ROUTING PROTOCOLS AND TRANSPORT LAYER INAD HOC

WIRELESS NETWORKS

Issues in designing a routing

Transport Layer protocol for Ad hoc networks

Proactive routing

Reactive routing (on-demand)

Hybrid routing

Classification of Transport Layer solutions

TCP overAd hoc wireless Networks.

3

UNIT III

ROUTING PROTOCOLS AND TRANSPORT LAYER IN

AD HOC WIRELESS NETWORKS

Issues in designing a routing and Transport Layer protocol for Ad hoc networks-

proactive routing, reactive routing (on-demand), hybrid routing- Classification of

Transport Layer solutions-TCP over Ad hoc wireless Networks.

PART- A

1. Define Routing. What are the design constraints of routing protocol?

Routing is process of establishing a path between sender and receiver nodes for

transmitting the packets along the path.

Design constraints:

Node Mobility

High dynamic topology

No infrastructure for centralized administration

Bandwidth constraint

Energy constrained

Establishing end to end path

2. What are the types of Ad hoc Routing Protocol?[May/June’16]

Ad hoc wireless network routing protocols can be classified into three

majorcategories based on the routing information update mechanism. They are

1. Proactive or table-driven routing protocols

2. Reactive or on-demand routing protocols

3. Hybrid routing protocols

3. What do you mean the proactive routing protocols? List the advantages

and disadvantages of it. .[May/June’15 &’16]

4

It is a Table-Driven routing Protocol, every node maintains the network topology

information in the form of routing tables by periodically exchanging routing. Routing

table contains up to date information. The Table information updated periodically to

maintain current stable or available path. This can be achieved by broadcasting beacon

signal between nodes.

Advantages:

o Min.time is required to find a path for data transmission.

Disadvantages:

o Frequent change in topology

o Network overload is high. Bandwidth consumption is high.

o Not suited for large networks.

4. What are the issues in designing routing protocols for adhoc wireless

networks?

Mobility

Bandwidth Constraint

Error Prone Shared Broadcast Radio Channel

Hidden and exposed terminal problem

Resource Constraints

Security Issues

5. How did the routing protocols are classified?

Routing protocols for ad hoc wireless networks can be classified into several types

based on different criteria. Routing protocol can be broadly classified into four

categories:

– Routing information update mechanism

– Use of temporal information for routing

– Routing topology

– Utilization of specific resource

6. List the advantages and disadvantages of reactive routing protocols.

Advantages:

o Less control messages

5

o Network overload is low. Bandwidth wastage is low.

o Suitable for large networks

Disadvantages:

o Time taken to discover a path is non predictable.

7. What are on-demand routing protocols?

On-demand routing protocols execute the path-finding process and exchange routing

information only when a path is required by a node to communicate with a destination. It

works on the basis of Route discovery and Route maintenance functions.

The protocols are,

o Dynamic source routing protocols (DSR)

o Ad-hoc on demand distance vector routing protocols (AODV)

o Temporally ordered routing Algorithm (TORA)

8. Ad hoc On-demand Distance Vector Routing (AODV)(OR) Reactive

Routing[May/June’15].

Protocols that fall under this category do not maintain the network topology

information. They obtain the necessary path when it is required, by using a

connection establishment process.

9. What do you meant by Hybrid Routing?

Protocols belonging to this category combine the best features of the above two

categories. Nodes within a certain distance from the node concerned, or within a

particular geographical region, are said to be within the routing zone of the given

node.

10. What is the use Wireless Routing Protocol (WRP)?

The wireless routing protocol (WRP) similar to DSDV, inherits the properties of

the distributed Bellman-Ford algorithm. To counter the count-to infinity problem

and to enable faster convergence, it employs a unique method of maintaining

information regarding the shortest distance to every destination node in the

network.

6

11. Define Dynamic Source Routing (DSR).

Dynamic source routing protocol (DSR) is an on-demand protocol designed to

restrict the bandwidth consumed by control packets in ad hoc wireless networks

by eliminating the periodic table-update messages required in the table-driven

approach. The major difference between this and the other on-demand routing

protocols is that it is beacon-less and hence does not require periodic

hellopacket (beacon) transmissions, which are used by a node to inform its

neighbors of its presence.

12. What is Associative-Based Routing (ABR)?

Associativity-based routing (ABR) protocol is a distributed routing protocol that

selects routes based on the stability of the wireless links. It is a beacon-based,

on-demand routing protocol. A link is classified as stable or unstable based on its

temporal stability.

13. Define Signal Stability-Based Adaptive Routing Protocol (SSA).

Signal stability-based adaptive routing protocol (SSA) [15] is an on-demand

routing protocol that uses signal stability as the prime factor for finding stable

routes. This protocol is beacon-based, in which the signal strength of the beacon

is measured for determining link stability. The signal strength isused to classify a

link as stable or unstable. This protocol consists of two parts:

forwarding protocol (FP)

dynamic routing protocol (DRP)

14. State Zone Routing Protocol (ZRP).

Zone routing protocol (ZRP) is a hybrid routing protocol which effectively

combines the best features of both proactive and reactive routing protocols. The

key concept employed in this protocol is to use a proactive routing scheme within

a limited zone in the r-hop neighborhood of every node, and use a reactive

routing scheme for nodes beyond this zone.

7

15. What is LAR?

Location-aided routing protocol (LAR) utilizes the location information for

improving the efficiency of routing by reducing the control overhead. LAR

assumes the availability of the global positioning system (GPS) for obtaining the

geographical position information necessary for routing.LAR designates two

geographical regions for selective forwarding of control packets, namely,

ExpectedZone and RequestZone.

16. What is CEDAR?

Core extraction distributed ad hoc routing (CEDAR) integrates routing and

support for QoS. It is based on extracting core nodes (also called as dominator

nodes) in the network, which together approximate the minimum dominating set.

A dominating set (DS) of a graph is defined as a set of nodes in the graph such

that every node in the graph is either present in the DS or is a neighbor of some

node present in the DS. CEDAR uses the core broadcast mechanism to transmit

any packet throughout the network in the unicast mode, involving as minimum

number of nodes as possible.

17. What are the issues in designing a transport layer protocol for ad hoc

wireless networks?

o Induced traffic

o Induced throughput unfairness

o Separation of congestion control, reliability, and flow control

o Power and bandwidth constraints

o Misinterpretation of congestion

o Completely decoupled transport layer

o Dynamic topology

18. What are design goals of a transport layer protocol for ad hoc wireless

networks?

o The protocol should maximize the throughput per connection.

8

o It should provide throughput fairness across contending flows.

o The protocol should incur minimum connection setup and connection

maintenance overheads. It should minimize the resource requirements for

setting up and maintaining the connection in order to make the protocol

scalable in large networks.

o The protocol should be able to adapt to the dynamics of the network such

as the rapid change in topology and changes in the nature of wireless

links from uni-directional to bidirectional or vice versa.

19. Give the classifications of transport layer solutions for ad hoc wireless

networks.

20. Why Does TCP Not Perform well in Ad Hoc Wireless Networks?

o Misinterpretation of packet loss

o Frequent path breaks

o Effect of path length

o Misinterpretation of congestion window

o Asymmetric link behavior

o Uni-directional path

21. What do you mean by Feedback-Based TCP?

Feedback-based TCP [also referred to as TCP feedback (TCP-F) proposes

modifications to the traditional TCP for improving performance in ad hoc wireless

9

networks. It uses a feedback-based approach. TCP-F requires the support of a

reliable link layer and a routing protocol that can provide feedback to the TCP

sender about the path breaks.

PART - B

1. Discuss in detail about the Major issues in designing Routing Protocols

for Ad hoc networks.[May/June’15&’16][Nov/Dec’15].

The major challenges that a routing protocol designed for ad hoc wireless networks

faces are,

Mobility


Error Prone Shared Broadcast Radio Channel

Hidden and exposed terminal problem


Security Issues

Mobility

The network topology in an ad hoc wireless network is highly dynamic due to the

movement of nodes, hence an on-going session suffers frequent path breaks.

Disruption occurs either due to the movement of the intermediate nodes in the path or

due to the movement of end nodes.


Bandwidth is available in wired networks due to the advent of fiber optics and due to the

exploitation of wavelength division multiplexing (WDM) technologies. But in a wireless

network, the radio band is limited, and hence the data rates it can offer are much less

than what a wired network can offer. This requires that the routing protocols use the

bandwidth optimally by keeping the overhead as low as possible.

.

Error-Prone Shared Broadcast Radio Channel

10

The broadcast nature of the radio channel poses a unique challenge in ad hoc wireless

networks. The wireless links have time-varying characteristics in terms of link capacity

and link-error probability. This requires that the ad hoc wireless network routing protocol

interacts with the MAC layer to find alternate routes through better-quality links.


Two essential and limited resources that form the major constraint for the nodes

in an ad hoc wireless network are battery life and processing power. Devicesused in ad

hoc wireless networks in most cases require portability, and hencethey also have size

and weight constraints along with the restrictions on thepower source. Increasing the

battery power and processing ability makes thenodes bulky and less portable. Thus ad

hoc wireless network routing protocolsmust optimally manage these resources.

Hidden and Exposed Terminal Problems

The hidden terminal problem refers to the collision of packets at a receiving node due to

the simultaneous transmission of those nodes that are not within the direct transmission

range of the sender, but are within the transmission range of the receiver. Collision

occurs when both nodes transmit packets at the same time without knowing about the

transmission of each other. In this case, node A did not successfully receive the CTS

originated by node R and hence assumes that there is no on-going transmission in the

neighborhood. Since node A is hidden from node T, any attempt to originate its own

RTS would result in collision of the on-going transmission between nodes T and R.

The exposed terminal problem refers to the inability of a node which is blocked due to

transmission by a nearby transmitting node to transmit to another node. Consider the

example in Figure 1.3. Here, if a transmission from node B to another node A is already

in progress, node C cannot transmit to node D, as it concludes that its neighbor, node

B, is in transmitting mode and hence should not interfere with the on-going

transmission.

Thus, reusability of the radio spectrum is affected. For node C to transmit

simultaneously when node B is transmitting, the transmitting frequency of node C must

be different from its receiving frequency.

11

Figure 1.2. Hidden terminal problem with RTS-CTS-Data-ACK scheme.

12

Figure1.3 Exposed terminal problem.

Characteristics of an Ideal Routing Protocol for Ad Hoc Wireless Networks

Due to the issues in an ad hoc wireless network environment discussed so far,

wired network routing protocols cannot be used in ad hoc wireless networks. Hence ad

hoc wireless networks require specialized routing protocols that address the challenges

described above. A routing protocol for ad hoc wireless networks should have the

following characteristics:

1. It must be fully distributed, as centralized routing involves high control overhead and

hence is not scalable. Distributed routing is more fault tolerant than centralized routing,

which involves the risk of single point of failure.

2. It must be adaptive to frequent topology changes caused by the mobility of nodes.

3. Route computation and maintenance must involve a minimum number of nodes.

Each node in the network must have quick access to routes, that is, minimum

connection setup time is desired.

13

4. It must be localized, as global state maintenance involves a huge state propagation

control overhead.

5. It must be loop-free and free from stale routes.

6. The number of packet collisions must be kept to a minimum by limiting the number of

broadcasts made by each node. The transmissions should be reliable to reduce

message loss and to prevent the occurrence of stale routes.

7. It must converge to optimal routes once the network topology becomes stable. The

convergence must be quick.

8. It must optimally use scarce resources such as bandwidth, computing power,

memory, and battery power.

9. Every node in the network should try to store information regarding the stable local

topology only. Frequent changes in local topology, and changes in the topology of parts

of the network with which the node does not have any traffic correspondence, must not

in any way affect the node, that is, changes in remote parts of the network must not

cause updates in the topology information maintained by the node.

10. It should be able to provide a certain level of quality of service (QoS) as demanded

by the applications, and should also offer support for time-sensitive traffic.

2. Explain Proactive (OR) Table-driven Routing and Hybrid Routing in

detail.[May/June’15 &’16](OR) [Nov/Dec’15] (Nov/Dec 2016)

These protocols are extensions of the wired network routing protocols. They

maintain the global topology information in the form of tables at every node. These

tables are updated frequently in order to maintain consistent and accurate network state

information. The destination sequenced distance-vector routing protocol (DSDV),

wireless routing protocol (WRP), source-tree adaptive routing protocol (STAR), and

14

cluster-head gateway switch routing protocol (CGSR) are some examples for the

protocols that belong to this category.

Destination Sequenced Distance-Vector Routing Protocol

The destination sequenced distance-vector routing protocol (DSDV) is one of the

first protocols proposed for ad hoc wireless networks. It is an enhanced version of the

distributed Bellman-Ford algorithm where each node maintains a table that contains the

shortest distance and the first node on the shortest path to every other node in the

network.

The table updates are of two types

Incremental updates

Full dumps

An incremental update takes a single network data packet unit(NDPU), while a full

dump may take multiple NDPUs. Incremental updates are used when a node does not

observe significant changes in the local topology. A full dump is done either when the

local topology changes significantly or when an incremental update requires more than

a single NDPU. Table updates are initiated by a destination with a new sequence

number which is always greater than the previous one. Upon receiving an updated

table, a node either updates its tables based on the received information or holds it for

some time to select the best metric (which may be the lowest number of hops) received

from multiple versions of the same update table from different neighboring nodes.

Based on the sequence number of the table update, it may forward or reject the table.

Figure 2.1 Route establishment in DSDV.

15

The reconfiguration of a path used by an on-going data transfer session ishandled by

the protocol in the following way. The end node of the broken linkinitiates a table update

message with the broken link's weight assigned to infinity (∞) and with a sequence

number greater than the stored sequence number for that destination. Each node, upon

receiving an update with weight∞, quickly disseminates it to its neighbors in order to

propagate the broken-link information to the whole network. Thus a single link break

leads to the propagation of table update information to the whole network.

All nodes receiving the new update message with the higher sequence number set the

new distance to node 11 in their corresponding tables. The updated table at node 1 is

shown in Figure2.2 where the current distance from node 1 to node 11 has increased

from three to four hops.

Figure 2.3. Route maintenance in DSDV.

16

The availability of routes to all destinations at all times implies that much less delay is

involved in the route setup process. The mechanism of incremental updates with

sequence number tags makes the existing wired network protocols adaptable to ad hoc

wireless networks. Hence, an existing wired network protocol can be applied to ad hoc

wireless networks with many fewer modifications.

Wireless Routing Protocol

The wireless routing protocol (WRP), similar to DSDV, inherits the properties of the

distributed Bellman-Ford algorithm. To counter the count-to infinity problem and to

enable faster convergence, it employs a unique method of maintaining information

regarding the shortest distance to every destination node in the network and the

penultimate hop node on the path to every destination node. Since WRP, like DSDV,

maintains an up-to-date view of the network, every node has a readily available route to

every destination node in the network.

17

From the routing table shown in Figure 2.4, the route from node 1 to node 15 has the

next node as node 2. The predecessor node of 15 corresponding to this route is node

12. The predecessor information helps WRP to converge quickly during link breaks.

Figure 2.4. Route establishment in WRP.

When a node detects a link break, it sends an update message to its neighbors with the

link cost of the broken link set to ∞. After receiving the update message, all affected

nodes update their minimum distances to the corresponding nodes (including the

distance to the destination). The node that initiated the update message then finds an

alternative route, if available from its DT. Note that this new route computed will not

contain the broken link.

Advantages and Disadvantages

18

WRP has the same advantages as that of DSDV. In addition, it has faster convergence

and involves fewer table updates. But the complexity of maintenance of multiple tables

demands a larger memory and greater processing power from nodes in the ad hoc

wireless network. At high mobility, the control overhead involved in updating table

entries is almost the same as that of DSDV and hence is not suitable for highly dynamic

and also for very large adhoc wireless networks.

Cluster-Head Gateway Switch Routing Protocol

The cluster-head gateway switch routing protocol (CGSR) uses a hierarchical network

topology, unlike other table-driven routing approaches that employ flat topologies.

CGSR organizes nodes into clusters, with coordination among the members of

each cluster entrusted to a special node named cluster head. This cluster-head is

elected dynamically by employing a least cluster change (LCC) algorithm . According to

this algorithm, a node ceases to be a cluster-head only if it comes under the range of

another cluster-head, where the tie is broken either using the lowest ID or highest

connectivity algorithm.

Clustering provides a mechanism to allocate bandwidth, which is a limited

resource, among different clusters, thereby improving reuse. A gateway is expected to

be able to listen to multiple spreading codes that are currently in operation in the

clusters in which the node exists as a member. A gateway conflict is said to occur when

a cluster-head issues a token to a gateway over a spreading code while the gateway is

tuned to another code. Gateways that are capable of simultaneously communicating

over two interfaces can avoid gateway conflicts.

When a cluster-head enters in another cluster, it cannot act as cluster-head;

member of new cluster. In CGSR, each node contains two tables.

• A cluster-member table

• A routing table

Cluster-Member Table :

This table maintains the duster-head of each destination node in that network.

Routing Table This table contains routing information such as destination flock, next

hop, metric and the sequence number. Each table is updated periodically at every node.

Before performing actual Packet transmission, each node has to receive a token from

its cluster-head. This token includes the information of destination cluster-head and the

19

next hop node information taken from the cluster-member table and the routing table of

its cluster-head.

The steps involved in packet transmission using CGSR are given below.

• When a node wants to send a packet to the node belongs to same cluster, it

forwards the packet directly to the cluster-head.

• Cluster-head checks whether the destination node belongs to that cluster or

not.

• If the destination node belongs to that cluster, then the cluster-head forwards

the packet to the destination node directly.

• Otherwise, the packet has to be forwarded to other cluster using gateways.

This step will be repeated until finding the destination node's cluster-head

• Once the destination node's cluster-head is identified, then the packet is

transmitted to the cluster-head of the destination node. This cluster-head will in turn

forward the packet directly to the intended destination.


CGSR is a hierarchical routing scheme which enables partial coordination between

nodes by electing cluster-heads. Hence, better bandwidth utilization is possible. It is

easy to implement priority scheduling schemes with token scheduling and gateway code

scheduling. The main disadvantages of CGSR are increase in path length and instability

in the system at high mobility when the rate of change of cluster-heads is high. In order

to avoid gateway conflicts, more resources (such as additional interfaces) are required.

The power consumption at the cluster-head node is also a matter of concern because

the battery-draining rate at the cluster-head is higher than that at a normal node. This

could lead to frequent changes in the cluster-head, which may result in multiple path

breaks.

Fisheye State Routing

Fisheye State Routing (FSR) is one of the table-driven routing protocols. In FSR,

each node broadcasts and exchanges the details of farthest node rather than

broadcasting neighbors information frequently in order to reduce the control overhead.

FSR protocol comprises three Phases

• Neighbor Discovery

• Information Dissemination

• Route Computation

20

Neighbor Discovery :

Each node maintains neighbor list and topology table. Initially these tables are

maintained as empty. Once the node initiates this neighbor discovery phase, then it can

fill the table with neighbor relationships. In order to identify the presence of neighbors,

each node broadcasts hello packet including its ID, time-to-live parameters. The nodes

hearing the packet will response with the reply message. Thus each node maintains

relationship between each other.

Information Dissemination :

This phase propagates Link State Packets (LSP). This phase handles two

functions : LSP integrity and updating interval. In LSP integrity, when a node generates

a new LSP, it must be flooded throughout the network. Most recently generated LSP

contains highest sequence number. Each node keeps track of sequence number that it

is used for the last LSP and inserts a next sequence number for the new LSP. A

sequence number is a counter value.

For each new LSP, counter value is incremented. Most recent sequence number

indicates the freshness of the message. The update interval is that the time gap

between 322sending first LSP and next LSP by a node. When a node receives a LSP to

retransmit, it calculates interval time to wait before sending out the LSP to other nodes

based on Update Interval calculation.

Update Interval = Constant Time * hop_count^ a

where Constant _Time is the user defined refresh period to send out LSPs (in the 1st

scope), hop _count is the number of hops the LSP has traversed, alpha is a parameter

that determines how much effect each scope has on the Update Interval . Values for

alpha are 0 or > 1.

HYBRID ROUTING PROTOCOLS

Each node maintains the network topology informationup to m hops. The different

existing hybrid protocols are presented below.

Core Extraction Distributed Ad Hoc Routing Protocol

Core extraction distributed ad hoc routing (CEDAR) integrates routing and support for

QoS. It is based on extracting core nodes (also called as dominator nodes) in the

network, which together approximate the minimum dominating set. A dominating set

(DS) of a graph is defined as a set of nodes in the graph such that every node in the

graph is either present in the DS or is a neighbor of some node present in the DS.

There exists at least one core node within three hops. The DS of the least cardinality in

21

a graph is called the minimum dominating set. Nodes that choose a core node as their

dominating node are called core member nodes of the core node concerned. The path

between two core nodes is termed a virtual link. CEDAR employs a distributed algorithm

to select core nodes. The selection of core nodes represents the core extraction phase.

CEDAR uses the core broadcast mechanism to transmit any packet throughout

the network in the unicast mode, involving as minimum number of nodes as possible.

These nodes that take part in the core broadcast process are called core nodes. In

order to carry out a core broadcast efficiently, each core node must know about its

neighboring core nodes. The transfer of information about neighboring core nodes

results in significant control overhead at high mobility.

When a core node to which many nodes are attached moves away from them,

each node has to reselect a new core node. The selection of core nodes, which is

similar to the distributed leader election process, involves substantial control overhead.

Route establishment in CEDAR is carried out in two phases.

The first phase finds a core path from the source to the destination. The core

path is defined as a path from the dominator of the source node (source core) to the

dominator of the destination node (destination core). In the second phase, a QoS

feasible path is found over the core path. A node initiates a RouteRequest if the

destination is not in the local topology table of its core node; otherwise, the path is

immediately established. For establishing a route, the source core initiates a core

broadcast in which the RouteRequest is sent to all neighboring core nodes as unicast

data. Each of these recipient core nodes in turn forwards the RouteRequest to its

neighboring core nodes if the destination is not its core member. A core node which has

the destination node as its core member replies to the source core. Once the core path

is established, a path with the required QoS support is then chosen.

To find a path that can provide the required QoS, the source core first finds a

path to the domain of the farthest possible core node in the core path, which can

provide the bandwidth required. Among the available paths to this domain, the

source core chooses the shortest-widest path (shortest path with highest

bandwidth). Assume MidCore is the farthest possible core node found by the

source core. In the next iteration, MidCore becomes the new source core and

finds another MidCore node that satisfies the QoS support requirements. This

22

iterative process repeats until a path to the destination with the required

bandwidth is found. If no feasible path is available, the source node is informed

about the non-availability of a QoS path.


The main advantage of CEDAR is that it performs both routing and QoS path

computation very efficiently with the help of core nodes. The increase- and decrease-

waves help in appropriate propagation of the stable high-bandwidth link information and

the unstable low-bandwidth link information, respectively. Core broadcasts provide a

reliable mechanism for establishing paths with QoS support.

A disadvantage of this protocol is that since route computation is carried out at

the core nodes only, the movement of the core nodes adversely affects the performance

of the protocol. Also, the core node update information could cause a significant amount

of control overhead.

Zone Routing Protocol

Zone routing protocol (ZRP) is a hybrid routing protocol which effectively

combines the best features of both proactive and reactive routing protocols. The key

concept employed in this protocol is to use a proactive routing scheme within a limited

zone in the r-hop neighborhood of every node, and use a reactive routing scheme for

nodes beyond this zone. An intra-zone routing protocol (IARP) is used in the zone

where a particular node employs proactive routing. The reactive routing protocol used

beyond this zone is referred to as inter-zone routing protocol (IERP). The routing zone

of a given node is a subset of the network, within which all nodes are reachable within

less than or equal to zone radius hops.

In Figure 2.1node 8 bordercasts RouteRequests to nodes 2, 3, 5, 7, 9, 10, 13,

14, and 15. If any peripheral node finds node d to be located within its routing zone, it

sends a Route Replyback to node s indicating the path; otherwise, the node

rebordercasts the RouteRequestpacket to the peripheral nodes. This process continues

until node d is located. Nodes 10 and 14 find the information about node 16 to be

available in their intra-zone routing tables, and hence they originate RouteReply packets

back to node 8. During RouteRequest propagation,every node that forwards the

RouteRequest appends its address to it. This information is used for delivering the

RouteReply packet back to the source. The path-finding process may result in multiple

23

RouteReply packets reaching the source, in which case the source node can choose

the best path among them. The criterion for selecting the best path may be the shortest

path, least delay path, etc.

Figure 2.1 Path finding between node 8 and node 16.


By combining the best features of proactive and reactive routing schemes, ZRP

reduces the control overhead compared to the RouteRequest flooding mechanism

employed in on-demand approaches and the periodic flooding of routing information

packets in table-driven approaches.

But in the absence of a query control, ZRP tends to produce higher control over

head than the aforementioned schemes. This can happen due to the large overlapping

of nodes' routing zones. The query control must ensure that redundant or duplicate

RouteRequests are not forwarded. Also, the decision on the zone radius has a

significant impact on the performance of the protocol.

Zone-Based Hierarchical Link State Routing Protocol

24

Zone-based hierarchical link state (ZHLS) routing protocol is a hybrid hierarchical

routing protocol that uses the geographical location information of the nodes to form

non-overlapping zones. A hierarchical addressing that consists of a zone ID and a node

ID is employed. Each node requires its location information, based on which it can

obtain its zone ID.

The information about topology inside a zone is maintained at every node inside

the zone, and for regions outside the zone, only the zone connectivity information is

maintained. ZHLS maintains high-level hierarchy for inter-zone routing. Packet

forwarding is aided by the hierarchical address comprising of the zone ID and

node ID. Similar to ZRP, ZHLS also employs a proactive approach inside the

geographical zone and a reactive approach beyond the zone. A destination node's

current location is identified by the zone ID of the zone in which it is present and is

obtained by a route search mechanism.

Data traffic between two zones will be relayed through these gateway nodes.

Using the information obtained from zone link state packets, a node can build the zone

topology. The zone routing table can be formed for any destination zone by executing

the shortest path algorithm on the zone-level topology. The zone link state packets are

source sequence numbered and a time-stamp field is included to avoid stale link state

packets.

Table. Zone link state packets

Figure 2.2 Zone-based hierarchical link state routing protocol.

25

Route maintenance is easier with the presence of multiple gateway nodes

between zones. If a given gateway node moves away, causing a zone-level connection

failure, routing can still take place with the help of the other gateway nodes. This is due

to the hierarchical addressing that makes use of zone ID and node ID. At any

intermediate zone, with the most updated inter-zonal routing table, it forwards the data

packets.


The hierarchical approach used in this protocol significantly reduces the storage

requirements and the communication overhead created because of mobility. The zone-

level topology is robust and resilient to path breaks due to mobility of nodes. Intra-zonal

topology changes do not generate network-wide control packet transmissions.

A main disadvantage of this protocol is the additional overhead incurred in the

creation of the zone-level topology. Also the path to the destination is sub-optimal. The

geographical information required for the creation of the zone level topology may not be

available in all environments.

26

3. Explain in detail about Reactive Routing. (OR) Discuss in detail about Ad

hoc On-demand Distance Vector Routing (AODV). [May/June’15 &’16].

ON-DEMAND ROUTING PROTOCOLS

The table-driven routing protocols, on-demand routing protocols execute the

path-finding process and exchange routing information only when a path is required by

a node to communicate with a destination. This section explores some of the existing

on- demand routing protocols in detail.

Dynamic Source Routing Protocol

Dynamic source routing protocol (DSR) is an on-demand protocol designed to restrict

the bandwidth consumed by control packets in ad hoc wireless networks by eliminating

the periodic table-update messages required in the table-driven approach. The major

difference between this and the other on demand routing protocols is that it is beacon-

less and hence does not require periodic hello packet (beacon) transmissions, which

are used by a node to inform its neighbors of its presence.

Figure 3.1. Route establishment in DSR.

27

Several optimization techniques have been incorporated into the basic DSR protocol to

improve the performance of the protocol. DSR uses the route cache at intermediate

nodes. The route cache is populated with routes that can be extracted from the

information contained in data packets that get forwarded. This cache information is used

by the intermediate nodes to reply to the source when they receive a routeRequest

packet and if they have a route to the corresponding destination

Figure 3.2. Route maintenance in DSR.

When an intermediate node in the path moves away, causing a wireless link to break,

for example, the link between nodes 12 and 15 in Figure 3.2 a RouteError message is

generated from the node adjacent to the broken link to inform the source node.


This protocol uses a reactive approach which eliminates the need to periodically

flood the network with table update messages which are required in a table driven

. The disadvantage of this protocol is that the route maintenance mechanism

does not locally repair a broken link.

28

Ad Hoc On-Demand Distance-Vector Routing Protocol

Ad hoc on-demand distance vector (AODV) routing protocol uses an on demand

approach for finding routes, that is, a route is established only when it is required by a

source node for transmitting data packets. It employs destination sequence numbers to

identify the most recent path.

The major difference between AODV and DSR stems out from the fact that DSR

uses source routing in which a data packet carries the complete path to be traversed.

A RouteRequest carries the source identifier (SrcID), the destination identifier (DestID),

the source sequence number (SrcSeqNum), the destination sequence number

(DestSeqNum), the broadcast identifier (BcastID), and the time to live (TTL) field.

DestSeqNum indicates the freshness of the route that is accepted by the source. When

an intermediate node receives a RouteRequest, it either forwards it or prepares a

RouteReply if it has a valid route to the destination.

Figure 3.3. Route establishment in AODV.

AODV does not repair a broken path locally. When a link breaks, which is determined

by observing the periodical beacons or through link-level acknowledgments, the end

29

nodes (i.e., source and destination nodes) are notified. When a source node learns

about the path break, it reestablishes the route to the destination if required by the

higher layers. If a path break is detected at an intermediate node, the node informs the

end nodes by sending an unsolicited RouteReply with the hop count set as ∞.Consider

the example illustrated in Figure 3.3. When a path breaks, forexample, between nodes

4 and 5, both the nodes initiate RouteError messages to inform their end nodes about

the link break. The end nodes delete thecorresponding entries from their tables. The

source node reinitiates the path finding process with the new BcastID and the previous

destination sequence number.

Figure 3.4. Route maintenance in AODV.


The main advantage of this protocol is that routes are established on demand

and destination sequence numbers are used to find the latest route to thedestination.

30

. Another disadvantage of AODV is that the periodic beaconing leads to

unnecessary bandwidth consumption.

Temporally Ordered Routing Algorithm

Temporally ordered routing algorithm (TORA) is a source-initiated on demand routing

protocol which uses a link reversal algorithm and provides loop-free multipath routes to

a destination node. In TORA, each node maintains its one-hop local topology

information and also has the capability to detect partitions.

Figure 3.5. Illustration of temporal ordering in TORA.

The route establishment function is performed only when a node requires a path to a

destination but does not have any directed link. This process establishes a destination-

oriented directed acyclic graph (DAG) using a Query/Update mechanism. Consider the

network topology shown in Figure 3.5

When an intermediate node (say, node 5) discovers that the route to the

destination node is invalid, as illustrated in Figure 3.6, it changes its distance value to a

higher value than its neighbors and originates an Update packet. The neighboring node

4 that receives the Update packet reverses the link between 1and 4 and forwards the

Update packet.

If the source node has no other neighbor that has a path to the destination, it

initiates a fresh Query/Update procedure. Assume that the link between nodes 1 and 4

breaks. Node 4 reverses the path between itself and node5, and sends an update

31

message to node 5. Since this conflicts with the earlier reversal, a partition in the

network can be inferred.

Figure 3.6. Illustration of route maintenance in TORA.


By limiting the control packets for route reconfigurations to a small region, TORA

incurs less control overhead. Concurrent detection of partitions and subsequent deletion

of routes could result in temporary oscillations and transient loops. The local

reconfiguration of paths results in non-optimal routes.

Location-Aided Routing

Location-aided routing protocol (LAR) utilizes the location information for

improving the efficiency of routing by reducing the control overhead. LAR assumes the

availability of the global positioning system (GPS)for obtaining the geographical position

information necessary for routing.

LAR designates two geographical regions for selective forwarding of control

packets, namely, Expected Zone and Request Zone.

32

Figure 3.7. Request Zone and Expected Zone in LAR1.

In the LAR1 algorithm, the source node (say, S) explicitly specifies the Request-

Zone in the RouteRequestpacket.

Figure 3.8 Route establishment in LAR2.

33


LAR reduces the control overhead by limiting the search area for finding a path.

The efficient use of geographical position information, reduced control overhead, and

increased utilization of bandwidth are the major advantages of this protocol.

Associativity-Based Routing

Associativity-based routing (ABR) protocol is a distributed routing protocol that

selects routes based on the stability of the wireless links. It is a beacon-based, on-

demand routing protocol. A link is classified as stable or unstable based on its temporal

stability.

In Figure 3.9 the RouteRequest reaches the destination through three different

routes. Route 1is 1-5-10-14-15, route 2 is 1-5-4-12-15, and route 3 is 1-2-4-8-13-15.

ABR selects route 3 as it contains the highest percentage of stable links compared to

route 1 and route 2. ABR gives more priority to stable routes than to shorter routes.

Hence, route 3 is selected even though the length of the selected route is more than

that of the other two routes.

Figure3.9. Route establishment in ABR.

34

If a link break occurs at an intermediate node, the node closer to the source, which

detects the break, initiates a local route repair process. In this process, the node locally

broadcasts a route repair packet, termed the local query (LQ) broadcast, with a limited

time to live (TTL)

Figure 3.10. Route maintenance in ABR.

Consider the example in Figure 7.19. When a path break occurs between nodes 8 and

13, the node adjacent to the broken link toward the source node, that is, node 8,

initiates a local query broadcast in order to locally repair the broken path. The local

query has limited scope with the maximum TTL value set to the remaining path length

from the broken link to the destination. In the same figure, the broken path is repaired

locally by bypassing the path segment 8-13- 15 through segment 8-12-15.


In ABR, stable routes have a higher preference compared to shorter routes. They result

in fewer path breaks which, in turn, reduces the extent of flooding due to reconfiguration

of paths in the network. One of the disadvantages of this protocol is that the chosen

path may be longer than the shortest path between the source and destination because

35

of the preference given to stable paths. Another disadvantage is that repetitive LQ

broadcasts may result in high delays during route repairs.

Signal Stability-Based Adaptive Routing Protocol

Signal stability-based adaptive routing protocol (SSA) is an on-demand routing

protocol that uses signal stability as the prime factor for finding stable routes.

This protocol is beacon-based, in which the signal strength of the beacon is

measured for determining link stability. The signal strength is used to classify a link as

stable or unstable. This protocol consists of two parts: forwarding protocol (FP) and

dynamic routing protocol (DRP).

Figure 3.11. Route establishment in SSA.

As shown in Figure 3.11, when a link breaks, the end nodes of the broken link (i. e.,

nodes 2 and 4) notify the corresponding end nodes of the path (i. e., nodes 1 and 15). A

source node, after receiving a route break notification packet, rebroadcasts the

RouteRequest to find another stable path to the destination. Stale entries are removed

only if data packets that use the stale route information fail to reach the next node. If the

link between nodes 2 and 4 breaks, a new strong path is established through 1-5-4-8-

13-15. If no strong path is available when a link gets broken (e.g., link 8-13), then the

36

new route is established by considering weak links also. This is done when multiple

RouteRequest attempts fail to obtain a path to the destination using only the stable

links.

Figure 3.12. Route maintenance in SSA.


The main advantage of this protocol is that it finds more stable routes when compared

to the shortest path route selection protocols such as DSR and AODV. This protocol

accommodates temporal stability by using beacon counts to classify a link as stable or

weak.

The main disadvantage of this protocol is that it puts a strong RouteRequest

forwarding condition which results in RouteRequest failures. A failed RouteRequest

attempt initiates a similar path-finding process for a new path without considering the

stability criterion.

Flow-Oriented Routing Protocol

Flow-oriented routing protocol (FORP) is an on-demand routing protocol that employs a

prediction-based multi-hop-handoff mechanism for supporting time-sensitive traffic in ad

hoc wireless networks. This protocol has been proposed for IPv6-based ad hoc wireless

37

networks where quality of service (QoS) needs to be provided. FORP uses a unique

prediction-based mechanism that utilizes the mobility and location information of nodes

to estimate the link expiration time (LET). LET is the approximate lifetime of a given

wireless link. The minimum of the LET values of all wireless links on a path is termed as

the route expiry time (RET). Every node is assumed to be able to predict the LET of

each of its links with its neighbors. The LET between two nodes can be estimated using

information such as current position of the nodes, their direction of movement, and their

transmission ranges. The LET of the wireless link between two nodes a and b with

transmission range Tx, which are moving at velocity Va and Vb at angles Ta and Tb ,

respectively (refer to Figure 7.22 (a)), can be estimated as described below:

The route establishment procedure is shown in Figure 7.22 (b). In this case, the

path 1-5-4-8-13 (path 1) has a RET value of 7, whereas the path 1-5-10-12-13

(path 2) has a RET value of 5.

This indicates that path 1 may last longer thanpath 2. Hence the sender node

originates a Flow-SETUP through the reversepath 13-8-4-5-1.

FORP employs a proactive route maintenance mechanism which makes use of

the expected RET of the current path available at the destination.

38

Figure 3.13. Route establishment in FORP.

Figure 3.14 Route maintenance in FORP.

39


The use of LET and RET estimates reduces path breaks and their associated ill effects

such as reduction in packet delivery, increase in the number of out-of order packets,

and non-optimal paths resulting from local reconfiguration attempts. The proactive route

reconfiguration mechanism adopted here works well when the topology is highly

dynamic. The requirements of time synchronization increases the control overhead.

4. Explain in detail about Issues in Designing a Transport Layer Protocol

and its Goals for Ad hoc Wireless Network.[Nov/Dec’15]

ISSUES IN DESIGNING A TRANSPORT LAYER PROTOCOL

FOR AD HOC WIRELESS NETWORKS

In this section, some of the issues to be considered while designing a transport layer

protocol for ad hoc wireless networks are discussed.

• Induced traffic: Unlike wired networks, ad hoc wireless networks utilize multi-hop

radio relaying. A link-level transmission affects the neighbor nodes of both the sender

and receiver of the link. In a path having multiple links, transmission at a particular link

affects one upstream link and one downstream link. This traffic at any given link (or

path) due to the traffic through neighboring links (or paths) is referred to as induced

traffic. This is due to the broadcast nature of the channel and the location-dependent

contention on the channel. This induced traffic affects the throughput achieved by the

transport layer protocol.

• Induced throughput unfairness: This refers to the throughput unfairness at the

transport layer due to the throughput/delay unfairness existing at the lower layers such

as the network and MAClayers. For example, an ad hoc wireless network that uses

IEEE 802.11 DCF as the MAC protocol may experience throughput unfairness at the

transport layer as well. A transport layer protocol should consider these in order to

provide a fair share of throughput across contending flows.

• Separation of congestion control, reliability, and flow control: A transport layer

protocol can provide better performance if end-to-end reliability, flow control, and

congestion control are handled separately. Reliability and flow control are end-to-end

activities, whereas congestion can at times be a local activity. The transport layer flow

can experience congestion with just one intermediate link under congestion. Hence, in

40

networks such as ad hoc wireless networks, the performance of the transport layer may

be improved if these are separately handled. While separating these, the most

important objective to be considered is the minimization of the additional control

overhead generated by them.

• Power and bandwidth constraints: Nodes in ad hoc wireless networks face resource

constraints including the two most important resources: (i) power source and (ii)

bandwidth. The performance of a transport layer protocol is significantly affected by

these constraints.

• Misinterpretation of congestion: Traditional mechanisms of detecting congestion in

networks, such as packet loss and retransmission timeout, are not suitable for detecting

the network congestion in ad hoc wireless networks. This is because the high error

rates of wireless channel, location-dependent contention, hidden terminal problem,

packet collisions in the network, path breaks due to the mobility of nodes, and node

failure due to a drained battery can also lead to packet loss in ad hoc wireless networks.

Hence, interpretation of network congestion as used in traditional networks is not

appropriate in ad hoc wireless networks.

• Completely decoupled transport layer: Another challenge faced by a transport layer

protocol is the interaction with the lower layers. Wired network transport layer protocols

are almost completely decoupled from the lower layers. In ad hoc wireless networks, the

cross-layer interaction between the transport layer and lower layers such as the network

layer and the MAC layer is important for the transport layer to adapt to the changing

network environment.

• Dynamic topology: Some of the deployment scenarios of ad hoc wireless networks

experience rapidly changing network topology due to the mobility of nodes. This can

lead to frequent path breaks, partitioning and remerging of networks, and high delay in

reestablishment of paths. Hence, the performance of a transport layer protocol is

significantly affected by the rapid changes in the network topology.

Designing a Transport Layer Protocol and its Goals for Ad hoc Wireless

Network.[Nov/Dec’15]

The following are the important goals to be met while designing a transport

layer protocol for ad hoc wireless networks:

41

• The protocol should maximize the throughput per connection.

• It should provide throughput fairness across contending flows.

• The protocol should incur minimum connection setup and connection maintenance

overheads. It should minimize the resource requirements for setting up and maintaining

the connection in order to make the protocol scalable in large networks.

• The transport layer protocol should have mechanisms for congestion control and flow

control in the network.

• It should be able to provide both reliable and unreliable connections as per the

requirements of the application layer.

• The protocol should be able to adapt to the dynamics of the network such as the rapid

change in topology and changes in the nature of wireless links from uni-directional to

bidirectional or vice versa.

• One of the important resources, the available bandwidth, must be used efficiently.

• The protocol should be aware of resource constraints such as battery power and

buffer sizes and make efficient use of them.

• The transport layer protocol should make use of information from the lower layers in

the protocol stack for improving the network throughput.

• It should have a well-defined cross-layer interaction framework for effective, scalable,

and protocol-independent interaction with lower layers. The protocol should maintain

end-to-end semantics.

CLASSIFICATION OF TRANSPORT LAYER SOLUTIONS

The top-level classification divides the protocols as extensions of TCP for ad hoc

wireless networks and other transport layer protocols which are not based on TCP. The

42

solutions for TCP over ad hoc wireless networks can further be classified into split

approaches and end-to-end approaches.

Figure. Classification of transport layer solutions.

5. Elaborate the TCP over Ad hoc Networks. [April/May’15] (Nov/Dec 2016)

The transmission control protocol (TCP) is the most predominant transport layer

protocol in the Internet today. It transports more than 90% percent of the traffic on the

Internet. Its reliability, end-to-end congestion control mechanism, byte stream transport

mechanism

Feedback-Based TCP

Feedback-based TCP [also referred to as TCP feedback (TCP-F) proposes

modifications to the traditional TCP for improving performance in ad hoc wireless

networks. It uses a feedback-based approach. In TCP-F, an intermediate node, upon

detection of a path break, originates a route failure notification (RFN) packet. This RFN

packet is routed toward the sender of the TCP session. The TCP sender's information is

expected to be obtained from the TCP packets being forwarded by the node. The

intermediate node that originates the RFN packet is called the failure point (FP). Figure

5.1shows the operation of the TCP-FB protocol.

43

Figure 5.1 Operation of TCP-F.

TCP-F provides a simple feedback-based solution to minimize the problems arising out

of frequent path breaks in ad hoc wireless networks. At the same time, it also permits

the TCP congestion control mechanism to respond to congestion in the network.

TCP with Explicit Link Failure Notification

Holland and Vaidya proposed the use of TCP with explicit link failure notification (TCP-

ELFN) for improving TCP performance in ad hoc wireless networks. This is similar to

TCP-F, except for the handling of explicit link failure notification (ELFN) and the use of

TCP probe packets for detecting the route reestablishment. This can be implemented in

two ways:

(i) By sending an ICMP2destination unreachable(DUR) message to the sender,

(ii) By piggy-backing this information ontheRouteError3 message that is sent to the

sender.

when the network is temporarily partitioned, the path failure may last longer and this can

lead to the origination of periodic probe packets consuming bandwidth and power and

(ii) the congestion window used after a new route is obtained may not reflect the

achievable transmission rate acceptable to the network and the TCP receiver.

TCP-BuS

TCP with buffering capability and sequence information (TCP-BuS) is

similar to the TCP-F andTCP-ELFN in its use of feedback information from an

intermediate node on detection of a path break. But TCP-BuS is more dependent

on the routing protocol compared to TCP-F and TCP-ELFN.

Thesemessages are modified to carry TCP connection and segment information.

44

Upondetection of a path break, an upstream intermediate node called pivot node

(PN)] originates an explicit route disconnection notification (ERDN) message.

Adhoc TCP

Ad hoc TCP (ATCP) operates based on the feedback mechanism. Based on the

information received from intermediaries, a sender can change its state to anyone of the

following.

o Persist state

o Congestion control state

o Retransmit state

Split TCP:

Split-TCP splitting the transport layer objectives into congestion control and end-to-end

reliability. The congestion control is mostly a local phenomenon due to the result of high

contention and high traffic load in a local region. In the ad hoc wireless network

environment, this demands local solutions. At the same time, reliability is an end-to-end

requirement and needs end-to-end acknowledgments.

In addition to splitting the congestion control and reliability objectives, split-TCP splits a

long TCP connection into a set of short concatenated TCP connections (called

segments or zones) with a number of selected intermediate nodes (known as proxy

nodes) as terminating points of these short connections. The below figure illustrates the

operation of split-TCP where a three segment split-TCP connection exists between

source node 1 and destination node 15. A proxy node receives the TCP packets, reads

its contents, stores it in its local buffer, and sends an acknowledgment to the source (or

the previous proxy). This acknowledgment called local acknowledgment (LACK) does

not guarantee end-to-end delivery. The responsibility of further delivery of packets is

assigned to the proxy node. A proxy node clears a buffered packet once it receives

LACK from the immediate successor proxy node for that packet. Split-TCP maintains

the end-to-end acknowledgment mechanism intact, irrespective of the addition of zone-

wise LACKs. The source node clears the buffered packets only after receiving the end-

to-end acknowledgment for those packets.

45

Figure. An illustration of Split-TCP.

In Figure, node 1 initiates a TCP session to node 15. Node 4 and node 13 are

chosen as proxy nodes. The number of proxy nodes in a TCP session is determined by

the length of the path between source and destination nodes. Based on a distributed

algorithm, the intermediate nodes that receive TCP packets determine whether to act as

a proxy node or just as a simple forwarding node. The simplest algorithm makes the

decision for acting as proxy node if the packet has already traversed more than a

predetermined number of hops from the last proxy node or the sender of the TCP

session. In Figure , the path between node 1 and node 4 is the first zone (segment), the

path between nodes 4 and 13 is the second zone (segment), and the last zoneis

between node 13 and 15.

The proxy node 4, upon receipt of each TCP packet from source node 1, acknowledges

it with a LACK packet, and buffers the received packets. This buffered packet is

forwarded to the next proxy node (in this case, node 13) at a transmission rate

proportional to the arrival of LACKs from the next proxy node or destination. The

transmission control window at the TCP sender is also split into two windows, that is,

the congestion window and the end-to-end window.

46

The congestion window changes according to the rate of arrival of LACKs from the next

proxy node and the end-to-end window is updated based on the arrival of end-to-end

ACKs. Both these windows are updated as per traditional TCP except that the

congestion window should stay within the end to- end window. In addition to these

transmission windows at the TCP sender, every proxy node maintains a congestion

window that governs the segment level transmission rate.

47

UNIT IV

WIRELESS SENSOR NETWORKS (WSNS) AND MAC PROTOCOLS

Single node architecture:

Hardware and software components of a sensor node

WSN Network architecture

Data relaying and aggregation strategies

MAC layer protocols: self-organizing,

Hybrid TDMA/FDMA

CSMA based MAC

IEEE 802.15.4

48

UNIT IV WIRELESS SENSOR NETWORKS (WSNS) AND MAC PROTOCOLS

Single node architecture: hardware and software components of a sensor node - WSN

Network architecture: typical network architectures-data relaying and aggregation

strategies -MAC layer protocols: self-organizing, Hybrid TDMA/FDMA and CSMA based

MAC- IEEE 802.15.4.

PART - A

1. Define Sensor.[May/June’16]

Sensor is a device that is used to detect and monitor the changes occurring

in electrical or physical quantities and thereby produces an output in the form of

electrical or optical signal.

2. What are the issues of Sensor Nodes?[May/June’16]

The various issues of sensor nodes are given below:

Types of sensor

Power consumption

Environment in which sensor nodes is working

Computational capability

Sensing capability

Connectivity

Control of remote devices

3. Define Active Sensor.[May/June’15 &’16]

An active sensor is a sensing device that requires an external source of power to

operate active sensors contrast with passive sensors, which simply detect and

respond to some type of input from the physical environment.

4. What do you mean by Passive Sensor?

A passive sensor is a device that detects and responds to some type of input

from the physical environment. Passive sensor technologies gather target data

49

through the detection of vibrations, light, radiation, heat or other phenomena

occurring in the subject's environment.

5. What is EAR (Eavesdrop and Register) Protocol?

EAR protocol provides connection between sensor nodes under mobile and

static conditions. The mobile nodes can be used with the statistically deployed

sensor nodes to establish connections.

6. What are the types of Sensor?

Sensors are broadly classified into two categories

Active Sensors

Passive Sensors

7. What are the components in Single Node Architecture?

The basic components of a sensor node are as follows:

A sensing unit

A processing unit

A communication unit

A power supply unit

8. Define Data Aggregation.

Data aggregation is the process of collecting data from different sensor nodes

and combining it together by applying aggregate functions.

9. What are the various aggregation strategies used in WSN?

The various aggregation strategies used in WSN are given below:

Continuous Packet Sensing and Dissemination

Continuous Packet Collection and Dissemination

Programmed Packet Collection and Dissemination

Programmed Packet Aggregation and Dissemination

Programmed Demand Based Aggregation and Dissemination

Weighted Event and Demand Based Data Aggregation

10. Name the three phases used in EAR Protocol.

EAR Protocol uses the following three phases

Registration phase

50

Connection phase

Disconnection phase

PART - B

1. Discuss in detail about IEEE 802.15.4.[May/June’15&’16][Nov/Dec’15].

IEEE 802.15.4 IEEE 802.15.4 is a standard which specifies Low-Rate

Wireless Personal Area Networks (LR-WPANs). This standard was defined in 2003

and is maintained by the IEEE 802.15 workinggroup. IEEE supports many working

groups to develop wireless and wired communication standards. For example, 802.3

are exclusively defined for wired Ethernet and 802.11 are defined for wireless LANs

(WLANs), also known as Wi-Fi. The IEEE 802.15 group of standards specifies a

variety of Wireless Personal Area Networks (WPANs) which are widely used for

different applications. For instance, 802.15.1 is defined for Bluetooth, 802.15.3 is a

high-data-rate Ultra-Wideband (UWB) technology and 802.15.6 is mainly defined for

body area networks (BAN).

Services and Features of IEEE 802.15.4 The various features and

services provided by IEEE 802.15.4 are given below :

• Offers low-cost wireless link services for industrial and commercial

sensor and actuator devices.

• It provides ease of installation, reliable data transfer, short-range

operation, and extremely low cost for the devices which operates with limited power

and considerable throughput.

• The data rate offered 20 kb/s, 40 kb/s and 250 kb/s.

• The maximum transmission range is 10 to 30 m.

•Uses CSMA/CA and slotted CSMA/CA contention schemes.

• Provides low power consumption.

• Uses star or peer-to-peer topologies.

IEEE 802.15.4 Topologies

This standard supports for two types of network topologies :

• Star

• Peer-to-peer

51

Transport Layer in Ad Hoc Wireless Networks and Communication

Technologies

IEEE 802.15.4 Protocol Stack

The IEEE 802.15.4 standard defines the physical layer (PHY) and MAC

layer of the Open Systems Interconnection (OSI) model of network operation. The size

of the protocol stack of IEEE 802.15.4 is 28K bytes.

Fig 5.1 IEEE 802.15.4 STAR and Peer-to-Peer

Fig. 5.2 IEEE 802.15.4 Protocol Stack

Physical Layer :

https://en.wikipedia.org/wiki/File:IEEE_802.15.4_Star_P2P.svg

https://en.wikipedia.org/wiki/File:IEEE_802.15.4_protocol_stack.svg

52

The PHY layer defines frequency, power, modulation, and other conditions

of the wireless link. IEEE 802.15.4 operates on two frequency bands : 868/915 MHz

and 2400 MHz.

The data rate used in 2400 MHz PHY offers 16 channels with 250 kb/s

and the data modulation used is 16-ary orthogonal modulation. This standard uses

Direct Sequence Spread Spectrum (DSSS) modulation. Standard Binary Phase-Shift

Keying (BPSK) is used in the two low-speed versions and the Offset-Quadrature

Phase-Shift Keying (O-QPSK) is used for the higher-data-rate version. The receiver

sensitivity at 2.4 GHz is -85 dBm.

The data rate used in 868 MHz PHY offers one channel with 20 kb/s

whereas 915 MHz PHY offers 10 channels with 40 kb/s. In this standard, The BPSK

with differential encoding is used for data modulation and 15-chip m-sequence is used

as spreading code. The receiver sensitivity at 868/915 MHz band is -92 dBm.

MAC Layer

When many nodes contend for the channel, the MAC layer controls the

access of the common wireless channel. It provides fair sharing of the common

channel using suitable contention schemes. When the upper layers find out network

throughput degradation below a certain threshold, the MAC layer will invoke energy

detection algorithms to scan the energy level of the channel.

The MAC layer is also responsible such as flow control, beacon

management, channel access, acknowledged frame delivery, association and

disassociation, frame validations, network synchronization, maintaining the

guaranteed time slot mechanism.

Other Layers The upper layers of IEEE 802.15.4 consist of a network layer and

application layer. The network layer provides network configuration, network

manipulation, and message routing. The application layer provides the proposed

function of a device. The Logical Link Control (LLC) can access the MAC sublayer

through the Service Specific Convergence Sublayer (SSCS). This LLC sublayer is

responsible for the data transmission between . devices on a network. The SSCS is a

sublayer which defines a standard mechanism layers to access MAC and PHY layers.

53

2. Explain in detail about MAC Protocols for Wireless Sensor Network.

[May/June’15 &’16].

MAC PROTOCOLS FOR SENSOR NETWORKS

MAC protocols in sensor networks must create a network infrastructure to establish communication links among the thousands of randomly scattered sensors. It must also ensure fair and efficient sharing of communication resources among the nodes, so that the overall lifetime of the network can be maximized . There are three basic kinds of MAC protocols used in sensor networks:

Fixed allocation,

demand-based,

contention-based. Self-Organizing MAC for Sensor Networks (SMACS)

Self-organizing MAC for sensor (SMACS) networks and eavesdrop and register

(EAR) are two protocols which handle network initialization and mobility support,

respectively. SMACS is a distributed protocol for network initialization and link-layer

organization In this protocol, neighbor discovery and channel assignment take place

simultaneously in a completely distributed manner.

A communication link between two nodes consists of a pair of time slots, at a

fixed frequency, which is randomly chosen at the time of establishing the link. Such an

assignment is possible in sensor networks without interference from neighboring nodes

because the available bandwidth is much larger than the data rate required for a

message transmission between two nodes.

This scheme requires synchronization only between communicating neighbors,

in order to precisely define the slots to be used for their communication. Power is

conserved by turning off the transceiver during idle slots, and using a random wake-up

schedule during the network start-up phase.

Eavesdrop and Register (EAR) Protocol

The EAR protocol enables seamless connection of nodes under mobile and

stationary conditions. This protocol makes use of certain mobile nodes, besidesthe

existing stationary sensor nodes, to offer service to maintain connections.

Mobile nodes eavesdrop on the control signals and maintain neighbor

information. The mobile nodes assume full control over connections and can drop

connections when they move away. Mobility is hence made transparent

54

Hybrid TDMA/FDMA

This is a centrally controlled scheme which assumes that nodes communicate

directly to a nearby BS. A pure TDMA scheme minimizes the time for which a node has

to be kept on, but the associated time synchronization costs are very high. A pure

FDMA scheme allots the minimum required bandwidth for each connection.

The hybrid TDMA/FDMA scheme, proposed in, uses an optimum number of

channels, which gives minimum overall power consumption. This is found to depend on

the ratio of power consumption of transmitter to receiver. If the transmitter consumes

more power, a TDMA scheme is favored, since it can be switched off in idle slots to

save power.

On the other hand, the scheme favors FDMA when the receiver consumes

greater power. This is because, in FDMA, the receiver need not expend power for time

synchronization by receiving during the guard band between slots, which becomes

essential in a TDMA scheme.

CSMA-Based MAC Protocols

Traditional CSMA-based schemes are more suitable for point-to-point

stochastically distributed traffic flows. On the other hand, sensor networks have variable

but periodic and correlated traffic. A CSMA-based MAC protocol for sensor networks

has been described with the following.

S-MAC

T-MAC

D-MAC

B-MAC

X-MAC

Wise-MAC

The sensing periods of CSMA are constant for energy efficiency, while the back-

off is random to avoid repeated collisions. Binary exponential back-off is used to

maintain fairness in the network. An adaptive transmission rate control (ARC) is also

used, which balances originating and route-through traffic in nodes. This ensures that

nodes closer to the BS are not favored over farther nodes.

ARC uses linear increase and multiplicative decrease of originating traffic in a

node. The penalty for dropping route-through traffic is higher, since energy has already

been invested in making the packets reach until that node. ARC performs phase

changes, that is, it staggers the transmission times of different streams so that periodic

streams are less likely to collide repeatedly. Hence, CSMA based MAC protocols are

contention-based and are designed mainly to increase energy efficiency and maintain

fairness.

55

LOCATION DISCOVERY

The location information of sensors has to be considered during aggregation of sensed

data. This implies each node should know its location and couple its location information

with the data in the messages it sends. A low-power, inexpensive, and reasonably

accurate mechanism is needed for location discovery. A global positioning system

(GPS) is not always feasible because it cannot reach nodes in dense foliage or indoors.

It also consumes high power and makes sensor nodes bulkier. Two basic mechanisms

of location discovery are now described.

Indoor Localization

Indoor localization techniques [19] use a fixed infrastructure to estimate the location of

sensor nodes. Fixed beacon nodes are strategically placed in the field of observation,

typically indoors, such as within a building. The randomly distributed sensors receive

beacon signals from the beacon nodes and measure the signal strength, angle of

arrival, and time difference between the arrival of different beacon signals. Using the

measurements from multiple beacons, the nodes estimate their location. Some

approaches use simple triangulation methods, while others require a priori database

creation of signal measurements. The nodes estimate distances by looking up the

database instead of performing computations. However, storage of the database may

not be possible in each node, so only the BS may carry the database.

Sensor Network Localization

In situations where there is no fixed infrastructure available and prior measurements are

not possible, some of the sensor nodes themselves act as beacons. They have their

location information, using GPS, and these send periodic beacons to other nodes. In the

case of communication using RF signals, the received signal strength indicator (RSSI)

can be used to estimate the distance, but this is very sensitive to obstacles and

environmental conditions. Alternatively, the time difference between beacon arrivals

from different nodes can be used to estimate location, if RF or ultrasound signals are

used for communication. This offers a lower range of estimation than RSSI, but is of

greater accuracy. Localization algorithms require techniques for location estimation

depending on the beacon nodes' location. These are called multi-lateration (ML)

techniques. Some simple ML techniques are described in what follows :

• Atomic ML: If a node receives three beacons, it can determine its position by a

mechanism similar to GPS. This is illustrated in Figure .

56

Figure . Atomic multi-lateration

Iterative ML: Some nodes may not be in the direct range of three beacons. Once a node

estimates its location, it sends out a beacon, which enables some other nodes to now

receive at least three beacons. Iteratively, all nodes in the network can estimate their

location. This is shown in Figure. The drawback of this multi-hop method is that errors

are propagated, hence estimation of location may not be accurate.

Figure . Iterative multi-lateration.

57

Collaborative ML: When two or more nodes cannot receive at least three beacons each,

they collaborate with each other. As shown in Figure, node A and node B have three

neighbors each. Of the six participating nodes, four are beacons, whose positions are

known. Hence, by solving a set of simultaneous quadratic equations, the positions of A

and B can be determined.

Figure. Collaborative multi-lateration.

A directionality-based localization approach has been explored in. This assumes that

beacon nodes have broadcast capability to reach all nodes of the network, and a central

controller rotates the beacons with a constant angular velocity ω radians/s. A constant

angular separation is maintained between the beacon nodes. Nodes in the network

measure the angles of arrival of beacon signals to estimate their location. The errors in

this technique occur due to nonzero beam-width from the beacons. The beam is not a

straight line as theoretically imagined, but it has a finite width. Hence, the measurement

of the angle of the beacon signal will be inaccurate. The authors of [22] propose an

algorithm which derives the location of sensor nodes based mainly on information about

connectivity between nodes. The all pairs shortest paths algorithm is run on the network

graph, which has edges indicating connectivity between nodes. Hence, the shortest

distance between each pair of nodes is obtained. A mathematical technique called

multidimensional scaling (MDS), an O(n3) algorithm (where n is the number of sensors),

is used to assign locations to nodes such that the distance constraints are satisfied. The

obtained picture of the network could be a rotated or flipped version of the actual

network. If the actual positions of any three nodes in the network are known, then the

entire network can be normalized (rotated or flipped) to obtain a very accurate

localization of all other nodes.

3. Explain in detail about Data Relaying in Wireless Sensor Network.

Data relaying is the process by which queries or data are routed in the sensor

network. The data collected by sensor nodes has to be communicated to the BS or to any other node interested in the data. The node that generates data is called a source and the information to be reported is called an event.

58

Data diffusion

It consists of a two-step process of interest propagation and data propagation. An interest is a descriptor for a particular kind of data or event that a node is interested in, such as temperature, intrusion, or presence of bio-agents. For every event that a sink is interested in, it broadcasts its interest to its neighbors and periodically refreshes its interest. Flooding

In flooding, each node which receives a packet broadcasts it if the maximum

hop-count of the packet is not reached and the node itself is not the destination of the packet. This technique does not require complex topology maintenance or route discovery algorithms. • Implosion:

This is the situation when duplicate messages are sent to the same node. This occurs when a node receives copies of the same message from many of its neighbors. • Overlap:

The same event may be sensed by more than one node due to overlapping regions of coverage. This results in their neighbors receiving duplicate reports of the same event.

• Resource blindness:

The flooding protocol does not consider the available energy at the nodes and results in many redundant transmissions. Hence, it reduces the network lifetime. Gossiping

Gossiping is a modified version of flooding, where the nodes do not broadcast a

packet, but send it to a randomly selected neighbor. This avoids the problem of

implosion, but it takes a long time for a message to propagate throughout the network.

Though gossiping has considerably lower overhead than flooding, it does not guarantee

that all nodes of the network will receive the message. It relies on the random neighbor

selection to eventually propagate the message throughout the network.

Rumor Routing

Rumor routing is an agent-based path creation algorithm. Agents, or "ants," are

long-lived entities created at random by nodes. These are basically packets which are

circulated in the network to establish shortest paths to events that they encounter. They

can also perform path optimizations at nodes that they visit. When an agent finds a

node whose path to an event is longer than its own, it updates the node's routing table.

Sequential Assignment Routing

In a set of algorithms which performs organization and mobility management in

sensor networks is proposed. The sequential assignment routing (SAR) algorithm

59

creates multiple trees, where the root of each tree is a one-hop neighbor of the sink.

Each tree grows outward from the sink and avoids nodes with low throughput or high

delay.

Directed Diffusion

The directed diffusion protocol is useful in scenarios where the sensor nodes

themselves generate requests/queries for data sensed by other nodes, instead of all

queries arising only from a BS. Hence, the sink for the query could be a BS or a sensor

node.

The directed diffusion routing protocol improves on data diffusion using interest

gradients. Each sensor node names its data with one or more attributes, and other

nodes express their interest depending on these attributes. Attribute-value pairs can be

used to describe an interest in intrusion data as follows, where an interest is nothing but

a set of descriptors for the data in which the querying node is interested.

Sensor Protocols for Information via Negotiation (SPIN)

A family of protocols called sensor protocols for information via negotiation

(SPIN) is proposed in SPIN uses negotiation and resource adaptation to address the

deficiencies of flooding. Negotiation reduces overlap and implosion, and a threshold-

based resource-aware operation is used to prolong network lifetime. Meta-data, or data

describing data, is transmitted instead of raw data.

Cost-Field Approach

The cost-field approach considers the problem of setting up paths to a sink. It is a

two-phase process, the first phase being to set up the cost field, based on metrics such

as delay, at all sensor nodes, and the second being data dissemination using the costs.

At each node, the cost is defined as the minimum cost from that node to the sink, which

occurs along the optimal path. Explicit path information does not need to be maintained.

Geographic Hash Table

Geographic hash table (GHT) is a system based on data-centric storage, inspired

by Internet-scale distributed hash table (DHT) systems. GHT hashes keys into

geographic coordinates and stores a (key, value) pair at the sensor node nearest to the

hash value. The calculated hash value is mapped onto a unique node consistently, so

that queries for the data can be routed to the correct node. Stored data is replicated to

ensure redundancy in case of node failures, and a consistency protocol is used to

maintain the replicated data.

Small Minimum Energy Communication Network

Small minimum energy communication network (SMECN) is a protocol proposed

in to construct a sub-network from a given communication network. If the entire sensor

network is represented by a graph G, the subgraph G' is constructed such that the

60

energy usage of the network is minimized. The number of edges in G' is less than that

of G, but all nodes of G are retained in G'.

4. Explain Sensor node architecture in detail.[May/June’15 &’16](OR)

[Nov/Dec’15] (Nov/Dec 2016)

Sensor Node Architecture

A sensor node is a device that can be used in a sensor network for performing data

gathering, processing and communicating with other sensor nodes in the network.

following section explains the architecture of a sensor node.

Single Node Architecture

The basic components of a sensor node are as follows:

• A sensing unit

• A processing unit

• A communication unit

• A power supply unit

The architecture of a sensor node is shown in Fig.

Power Supply Unit

Fig. 5.2.1 Architecture of a sensor node

Sensing Unit :

Sensors are used to measure the physical quantifies like temperature, pressure

etc. from their environment. They are hardware devices; each sensor node is used to

Processing Unit

Sensing Unit Communication Unit

Memory

Micro-Controller

Micro Processor

Transceiver Sensor ADC

Battery

61

produce a quantifiable response to a change in temperature or pressure of the

environment.

Sensors produce analog signals. An Analog-to--Digital Converter (ADC) is used

to convert the analog signal into digital signals. The digitized signal can be sent to

controllers for further processing. Some sensors may contain the required electronic

components to convert the raw signals into readings. In general, sensor nodes are small

in size and consume energy during operation.

Processing Unit:

The micro-controller placed in the sensor is used to perform specific tasks, processes

data and controls the operation of other co to in the sensor node. of External memory is

used to store the od high storage capacity, collected information. Usually, flash

memories are used in sensor nodes due to their low cost and high storage capacity.

Communication Unit :

Sensor nodes use transceiver to communicate with other nodes. The communication

and infrared. wireless communication media used in sensor networks are radio

frequency, optical communication infrared.

Power Supply Unit :

Sensor node consumes power for sensing, communicating and data processing. Energy

required for data communication is more when data gathering, compare with other

process. Changing the battery in sensor node can be costl and inconvenient. So it is

very important to ensure that y at the sensor node has adequate energy for Performing

operations continuously.

Hardware Subsystems of a Sensor Node

The four basic hardware subsystems of a sensor node are given below :

• Computing subsystem

• Power supply subsystem

• Communication subsystem

• Sensing subsystem

62

Computing Subsystem:

Each sensor node consists of a microprocessor to control the sensor.

Microprocessor unit of every sensor node is responsible for executing and managing

communication protocols. This subsystem is also responsible for data processing and

manipulation, error correction and encryption, digital modulation and demodulation.

Power Supply Subsystem:

The life time of the sensor node depends upon the battery life. Batteries placed

in each sensor can have only limited power. Since sensor nodes receive power from

batteries, limited amount of power can be used for processing. The amount of power

being used by the sensor can be monitored by power supply subsystem. Depending

upon the operating environment of sensor node, power can be turned on or off. The

battery used in sensor node has to be charged from the suitable energy source and

hence make the sensor node to operate for prolong period.

Communication Subsystem

Short range radios are used to enable communication between sensor nodes

and with other wired units. Each sensor node can be in any one of the following mode :

• Transmit

• Receive

• Idle

• Sleep

63

UNIT V WSN ROUTING, LOCALIZATION & QOS

Issues in WSN routing

OLSR- Localization

Indoor and Sensor Network Localization

Absolute and relative localization

Triangulation

QOS in WSN

Energy Efficient Design

Synchronization

Transport Layer issues

64

UNIT V WSN ROUTING, LOCALIZATION & QOS

Issues in WSN routing – OLSR- Localization – Indoor and Sensor Network

Localization-absolute and relative localization, triangulation-QOS in WSN-Energy

Efficient Design-Synchronization-Transport Layer issues.

PART A

1. Write some of the issues in WSN Routing.

The various issues of WSN routing are,

• Energy constraint

• Scalability

• Transmission media

• Frequent occurrence of failure

• Hardware constraint

2. List the three types of control messages used in OLSR.

The three types of control messages used in OLSR are

•Hello message

• Topology Control (TC) message

• Multiple Interface Declaration (MID)

3. Define Localization and Name some of the popular localization

mechanisms used in WSN.

Localization is a technique used to determine the location of

sensor nodes. The popular localization mechanisms are,

GPS based localization

Indoor localization

Sensor network localization

Absolute localization

Relative localization

Triangulation localization

65

4. Define Multi-Lateration(ML).

The time difference between the reception of beacon signals

from different node used to determine the location. Some

localization techniques requires the location of bea nodes.

These techniques are called as Multi-Lateration (ML)

5. List out the QoS parameters used in WSN.

The QoS parameters used in WSN are,

• Throughput

• Delay

• Jitter

• Packet loss rate

6. Define Throughput

Throughput refers the number of data transmitted within

a given e. The higher throughput of the network promotes the

performance of the system.

7. Define Delay and Jitter.

Packet transmission delay is the elapsed time between

sending the packet from the source node to the time it is

received by the receiver.

Jitter is defined as variations in delay of received

packets at the receiver. It is mat caused by the queuing delay

variations in consecutive packets.

8. Define Packet Loss Rate and DVS.

It is referred as the percentage of packets lost during

packet transmission. This may happen due to congestion,

disconnection of path and mobility of nodes.

Dynamic Voltage Scaling (DVS) is used in WSNs to

reduce energy consumption.

66

9. What is DPM ?

The basic Dynamic Power Management (DPM) techniques can

be used to turn off the components of sensor nodes when no

operation is carried out.

10. Define Synchronization

Synchronization is a key concept of WSN used to

perform multi-hop wireless communication. This concept is

used to regularize the communication between the sender and

the receiver during packet transmission.

Part-B (Questions and Answers)

1. Explain in detail about QoS (Quality of Service) issues in Wireless

Sensor Network. [May/June’15 &’16]. (Nov/Dec 2016)

QoS provisioning often requires negotiation between host and network, call

admission control, resource reservation, and priority scheduling of packets. QoS can be rendered in ad hoc wireless networks through several ways, namely, per flow, per link, or per node.

In ad hoc wireless networks, the boundary between the service provider (network) and the user (host) is not defined clearly, thus making it essential to have better coordination among the hosts to achieve QoS.

Characteristics of ad hoc wireless networks such as lack of central coordination,

mobility of hosts, and limited availability of resources make QoS provisioning very challenging. The QoS parameters used in WSN are,

• Throughput

• Delay

• Jitter

• Packet loss rate

The purpose of a sensor network is to monitor and report events or phenomena taking place in a particular area. Hence, the main parameters which define how well the network observes a given area are "coverage" and "exposure."

67

Coverage

Coverage is a measure of how well the network can observe or cover an event. Coverage depends upon the range and sensitivity of the sensing nodes, and the location and density of the sensing nodes in the given region. The worst case coverage defines areas of breach, that is, where coverage is the poorest.

A path along the areas of best coverage is called a maximum support path or maximum exposure path.

The coverage problem is formally defined as follows: Given a field A with a set of

sensors S = {s1 , s2 , ...,sn}, where for each sensor siin S, its location coordinates (xi , yi) are known, based on localization techniques.

Areas I and F are the initial and final locations of an intruder traversing the field. The problem is to identify PB , the maximal breach path starting in I and ending in F. PB is defined as the locus of points pin the region A, where p is in PB if the distance from p to the closest sensor is maximized. Voronoidiagram.

It can be proved that the path PB will be composed of line segmentsthat belong to the Voronoi diagram corresponding to the sensor graph. In twodimensions, the Voronoi diagram of a set of sites is a partitioning of the planeinto a set of convex polygons such that all points inside a polygon are closest tothe site enclosed by the polygon, and the polygons have edges equidistant fromthe nearby sites. A Voronoi diagram for a sensor network, and a breach path from I to F, are shown in Figure 1.1. Figure 1.1. Voronoi diagram.

68

The algorithm to find the breach path PB is: • Generate the Voronoi diagram, with the set of vertices V and the set of edges E. This is done by drawing the perpendicular bisectors of every line segment joining two sites, and using their points of intersection as the vertices of the convex polygons. • Create a weighted graph

A weighted graph is created with vertices from V and edges from E, such that the

weight of each edge in the graph is the minimum distance from all sensors in S. The edge weights represent the distance from the nearest sensor. Smaller edge weights imply better coverage along the edge. Determine the maximum cost path from I to F, using breadth-first search. The maximum cost implies least coverage. Hence, the required breach path is along this maximum-cost path determined from the Voronoi diagram. Figure 1.2 Delaunay triangulation.

69

Exposure

Exposure is defined as the expected ability of observing a target in the sensor field. It is formally defined as the integral of the sensing function on a path from source node Ps to destination node Pd. The sensing power of a node s at point p is usually modeled as

where λ and k are constants, and d(s, p) is the distance of p from s. Consider a network with sensors s1 ,s2 , ..., sn . The total intensity at point p, called the all sensor field intensity, is given by

The closest-sensor field intensity at p is

70

where s min is the closest sensor to p. The exposure during travel of an event along a path p(t) is defined by the exposure function

is the elemental arc length, and t1 , t2 are the time instances between which the path is traversed. For conversion from Cartesian coordinates (x(t), y(t)),

Minimum Exposure Path (MEP) minimum exposure path (MEP) from (-1, -1) to (1, 1) is shown in Figure Unit field minimum exposure path.

It can also be proved that for a single sensor s in a polygonal field, with vertices

v1 , v2 , ..., vn, the MEP between two vertices vi and vj can be determined as follows. The edge (vi, vi+ 1 ) is tangent to the inscribed circle at ui. Then the MEP consists of the line segment from vi to ui, part of the inscribed circle from ui to uj, and the line segment from uj to vj.

Figure Polygon field minimum exposure path.

71

Points within the inscribed circle. For the generic exposure problem of

determining the MEP for randomly placed sensor nodes in the network, the network is tessellated with grid points. An example is shown in Figure .

To construct an n × n grid of order m, each side of a square is divided into m equal parts, creating (m + 1) vertices on the edge. Within each square, all vertices are connected to obtain a grid. Higher order grids have greater accuracy. For each edge in the grid network, the exposure function is used to determine the edge weights, and the MEP is defined as the shortest path, determined by Dijkstra's algorithm. Generic minimum exposure path.

The mathematical concept of exposure is important for evaluating the target

detection capability of a sensor network. Sensors are deployed in a given area to detect events occurring in the field of interest. The nodes collaborate among themselves (perform data fusion) through the exchange of localized information, and reach a decision about the location and movement of a given event or target.

Issues and challenges in providing QoS in ad hoc wireless networks

72

• Dynamically varying network topology: Since the nodes in an ad hoc wireless network do not have any restriction on mobility, the network topology changes dynamically. . • Imprecise state information: In most cases, the nodes in an ad hoc wireless network maintain both the link-specific state information and flow-specific state information. The link-specific state information includes bandwidth, delay, delay jitter, loss rate, error rate, stability, cost, and distance values for each link. . • Lack of central coordination: Unlike wireless LANs and cellular networks, ad hoc

wireless networks do not have central controllers to coordinate the activity of nodes. This further complicates QoS provisioning in ad hoc wireless networks. • Error-prone shared radio channel: The radio channel is a broadcast medium by

nature. During propagation through the wireless medium, the radio waves suffer from several impairments such as attenuation, multipath propagation, and interference (from other wireless devices operating in the vicinity) • Hidden terminal problem: The hidden terminal problem is inherent in ad hoc wireless networks. This problem occurs when packets originating from two or more sender nodes, which are not within the direct transmission range of each other, collide at a common receiver node. It necessitates the retransmission of the packets, which may not be acceptable for flows that have stringent QoS requirements. • Limited resource availability: Resources such as bandwidth, battery life, storage space, and processing capability are limited in ad hoc wireless networks. • Insecure medium: Due to the broadcast nature of the wireless medium,

communication through a wireless channel is highly insecure. Therefore, security is an important issue in ad hoc wireless networks, especially for military and tactical applications. • Hard state versus soft state resource reservation: QoS resource reservation is one of the very important components of any QoS framework (a QoS framework is a complete system that provides required/promised services to each user or application). It is responsible for reserving resources at all intermediate nodes along the path from the source to the destination, as requested by the QoS session. • Stateful versus stateless approach: In the stateful approach, each node maintains either global state information or only local state information, while in the case of a stateless approach, no such information is maintained at the nodes. State information includes both the topology information and the flow specific information

2. Explain the issues in Transport Layer Protocol detail.[May/June’15

&’16](OR) [Nov/Dec’15]

Transport Layer Issues WSNs.

73

Each transport layer protocol has to provide end-to-end reliable packet

delivery, It responsible for managing network congestion issues of WSNs.

The Transmission Control Protocol (TCP) developed for ad hoc networks are

not well suited for adapted to the WSN and has to be made to suit for change

of environment, The various challenges of transport layer protocols are

discussed in the following sections.

Challenges

The major challenges of transport layer protocols used in WSNs are given

below :

• Providing reliable data delivery

• Configuring sensor node to suit for the specific application

• High packet loss due to poor link condition

• Rapid change of network topology

• Multipath routing

• Frequent path break in end-to-end connectivity due to node failure

• End-to-end error recovery

A WSN transport layer protocols such as Pump Slowly, Fetch Quickly

(PSFQ) and Event.. to-Sink Reliable Transport (ESRT) protocol have been

designed to provide simple, reliable and guaranteed data delivery. The PSFQ

protocol and ESRT protocols are explained in the following sections.

Pump Slowly, Fetch Quickly Protocol

In PSFQ, the sensor which sends data to other sensors must ensure that the

transmission is taken place slowly i.e. pump data slowly. This process is

called 'pump slowly'. This approach avoids high packet loss rate. If a sensor

node identifies packet loss, then the sensor node should recover (fetch) the

missing packets. This process is called "fetch quickly'. This quick recovery

process will minimize the lost recovery cost.

Error Recovery

Performing end-to-end error recovery is not feasible in WSNs. PSFQ uses a

key concept called hop-by-hop error recovery. In this mechanism, all the

intermediate sensor nodes are taking the responsibility for error recovery.

Data exchange is performed on a hop-by-hop basis rather than performing

74

end-to-end basis. In WSNs, the lost or erroneous packet has to be

retransmitted. Sometimes each hop may receive multiple number of same

packets. This consumes more energy. All the packets has to be maintained in

the receiver's queue until receiving error-free packets.

Protocol Functions

PSFQ uses the following key functions

• Message relaying

• Relay-Initiated error recovery

• Selective slaws reporting

Message ,relaying (pump operation) :

Each sensor node inject the sensed data into the network. I hose message

can be received by the neighboring nodes and can be buffered for f•liiyilig the

packets to other nodes within the hounded time limit. Pump operation works

as follows. The pump Operation slowly "pumps" or injects data to the WSN. A

sender node sends 3 packet to other sensor. After receiving this packet, the

sensor will check the data with its local data cache. If the received packet's

sequence number is same as cached packet, then it i will discard the

duplicate packet. If this is a new message, PSFQ will buffer the packet in

packet cache.

Relay-initiated error recovery (fetch operation) :

A sensor node which relays (forwards) the packet will maintain the data in

a data cache. If the node detects any packet loss or the packets are received

with unordered sequence numbers, then the packet is retransmitted from the

intermediate node. This is possible if the lost data is already buffered at the

intermediate node. So the sensor node which detects the packet loss may

initiate error recovery mechanism by sending ACK and Negative

Acknowledgement messages (NACK).

Selective status reporting (report operation) :

Each sensor node observes the status of the already sent packets in the

network to know the error rate. Based on the error rate of the previous

transmissions, the sensor node takes decision for further data transmission. If

75

a report message cannot able to append more status information, then new

report message will be created.

Event-to-Sink Reliable Transport (ESRT) Protocol

ESRT protocol provides a solution for transport layer issues. It provides

reliable event detection and congestion resolution with minimum energy

consumption. This protocol offers event-to-sink reliability rather than providing

end-to-end reliability. This can be achieved when data about the event is

carried out reliably to the sink node.

Some of the salient features of ESRT protocol are given below :

• Self configuration

• Energy awareness

• Congestion control

• Collective identification

• Biased implementation

Self-configuration:

ESRT protocol supports for dynamic topology !formed by WSN arid

achieves flexibility in self-configuring the network when topology changes.

Energy Awareness : The minimum possible energy consumption can be

achieved reducing reporting rates.

Congestion Control : Several packet losses may occur due to congestion at

the sink node.

Collective Identification : In general, sink nodes show interest in collecting

other sensor nodes and will send collective information to the required node

or center. Ti-provides the implementation of event-to-sink model and thereby

reducing network overhead.

Biased Implementation: ESRT operates on sink nodes with Minimum

functionalities and roves reliability. thereby reducing heavy load at sink nodes.

In ESRT, each sink node is expected to receive collective report from each

sensor node.

The ESRT protocol offers two types of reliabilities achieved. by

• Observed reliability

76

• Required reliability

Observed Reliability (OR) : It is termed as the number of data packets that

is carried out from event to the sink node.

Required Reliability (RR) : It is termed as the number of data packets to be

effectively tracked for an event. If the observed reliability is greater than the

desired reliability, then the event is considered to be reliably detected.

Otherwise, the required steps have to be taken to attain the desired reliability.

If OR falls below the requirement, then the protocol must increase the

reporting frequency. Further, if the RR exceeds, then the reporting frequency

must be reduced. The information about the number of reporting frequencies

of the event will be broadcast by the sink node to all the other sensors.

3. Elaborate the various Synchronization techniques. [April/May’15]

OTHER ISSUES The issues that are recently being explored in sensor networks, such as energy-

efficient hardware and architecture, real-time communication on sensor networks, transport layer protocols, and security issues. Because these are mostly in the research stage, there are many improvements to be made on these fronts. Energy-Efficient Design

Energy optimization in sensor networks must prolong the life of a single node as well as of the entire network. Power saving in the micro-controller unit has been analyzed in , where the power required by different processors has been compared. The choice of the processor should be application-specific, such that performance requirements are met with the least power consumption. Computation can be carried out in a power-aware manner using dynamic power management (DPM). One of the basic DPM techniques is to shut down several components of the sensor node when no events take place. The processor has a time-varying computational load, hence the voltage supplied to it can be scaled to meet only the instantaneous processing requirement. This is called dynamic voltage scaling (DVS).

The software used for sensor networks such as the operating system, application software, and network software can also be made energy-aware. The real-time task scheduler should actively support DVS by predicting the computation and communication loads. Sensor applications can use a trade-off between energy and accuracy by performing the most significant operations first, so that premature termination of the computation due to energy constraints does not affect the result by a large margin.

77

The communications subsystem should also perform energy-aware packet forwarding. The use of intelligent radio hardware enables packets to be forwarded directly from the communication subsystem, without processing it through the micro-controller. Techniques similar to DVS are used for modulation, to transmit data using a simpler modulation scheme, thereby consuming less energy, when the required data transmission rate is lower. This is called modulation scaling. Besides incorporating energy-efficient algorithms at the node level, there should be a network-wide cooperation among nodes to conserve energy and increase the overall network lifetime. The computation-communication trade-off determines how much local computation is to be performed at each node and what level of aggregated data should be communicated to neighboring nodes or BSs. Traffic distribution and topology management algorithms exploit the redundancy in the number of sensor nodes to use alternate routes so that energy consumption all over the network is nearly uniform. Synchronization

Synchronization among nodes is essential to support TDMA schemes on multihop wireless networks. Also, time synchronization is useful for determining the temporal ordering of messages sent from sensors and the proximity of the sensors. Usually, sensor nodes are dropped into the environment from which data has to be collected, and their exact positions are not fixed before deployment. Hence, synchronization is the only way by which the nodes can determine their relative positions. Further, in order to furnish aggregate data to the monitor node, the sensors must evolve a common timescale using their synchronized clocks, to judge the speed of a moving target or phenomenon.

Sensors must be able to recognize duplicate reports of the same event by different nodes and discard them, which means that the node must be able to precisely determine the instant of time at which the event occurred. There are two major kinds of synchronization algorithms: one which achieves long-lasting global synchronization, that is, lasts throughout the network for its entire lifetime, and one which achieves a short-lived or pulse synchronization where the nodes are synchronized only for an instant. Synchronization protocols typically involve delay measurements of control packets. The delays experienced during a packet transmission can be split into four major components [28]: send time, access time, propagation time, and receive time. The send time is the time spent at the sender to construct the message. The access time is the time taken by the MAC layer to access the medium, which is appreciable in a contention-based MAC protocol.

The propagation time reflects the time taken by the bits to be physically transmitted through the medium over the distance separating the sender and receiver. The receive time is the time for processing required in the receiver's network interface to receive the message from the channel and notify the host of its arrival. If the arrival time is time-stamped at a low layer, overheads of context switches and system calls are avoided, and the arrival time-stamp closely reflects the actual arrival time, with the only non-determinism introduced being due to reception of the first bit. Many existing synchronization algorithms for sensor networks rely on the time information obtained through the GPS to provide coarse time synchronization.

The accuracy of time synchronization provided by GPS depends on the number of satellites observed by the GPS receiver. In the worst case, with only one observed

78

satellite, GPS offers an accuracy of 1 μs However, GPS is not a suitable choice for sensor networks because GPS receivers cannot be used inside large buildings and basements, or underwater, or in other satellite unreachable environments where sensor networks may have to be deployed. A low-power synchronization scheme called post facto synchronization has been proposed by Elson and Estrin in [30] for wireless sensor networks. In this scheme, the clocks of the nodes are normally unsynchronized. When an event is observed, a synchronization pulse is broadcast by a beacon node, with respect to which all nodes normalize their time-stamps for the observation of the event.

This scheme offers short-lived synchronization, creating only an "instant" of synchronization among the nodes which are within transmission range of the beacon node. The propagation delay of the synchronization pulse is assumed to be the same for all nodes.

A node becomes a leader when elected by a majority of nodes in the network. A distributed election protocol is used which ensures the presence of a unique leader for the network. The leader then periodically sends synchronization messages to its neighbors. These messages are broadcast in turn to all nodes of the network. The time-difference bounds have been theoretically analyzed, and fault tolerance techniques have been added to account for errors in the synchronization messages.

A long-lasting synchronization protocol is proposed in, which ensures global synchronization of a connected network, or synchronization within connected partitions of a network. Each node in the network maintains its own local clock (real clock) and a virtual clock to keep track of its leader's clock. A unique leader is elected for each partition in the network, and virtual clocks are updated to match the leader's real clock.

The leader election process occurs as follows. On power-up, every node makes an attempt to either locate a leader in its partition or claims to be a leader itself. A node decides, with a small probability, to stake a claim for leadership and announces its claim with a random number sent on the claim packet. This Leader Announcement packet also contains the transmission power used by the node. A node which receives this claim applies a correction for the propagation delay experienced by the claim packet (calculated based on received power), and updates its virtual clock to the expected value of the leader's real clock at that instant.

Time-stamping of claims is performed at the physical layer, to avoid the variable queuing and medium access delays introduced by the MAC layer. The claim is flooded throughout the partition, bounded by a TTL field. In case two nodes within a partition stake a leadership claim, the one whose Leader Announcement has a higher random number resynchronizes to the leader whose Leader Announcement has the lower random number, and then rebroadcasts the Leader Announcement of the node that generated the lower random number. In the highly unlikely case of two leaders generating the same random number, node ID is used for resolution. Periodic beaconing ensures that synchronization is maintained throughout the partition, and nodes which join it later also synchronize their clocks.

Resynchronization is the process of synchronizing different network partitions that are independently synchronized to different clocks to a common clock. In dynamic networks such as sensor networks, frequent changes in topology make resynchronization an important issue. Resynchronization takes place in situations such

79

as the merging of two partitions due to mobility, where all clocks in a partition may need to be updated to match the leader of the other partition, as shown in Figure. Figure. Resynchronization.

The typical TDMA superframe structure is shown in Figure . Presynch frames define the start and end of a superframe, control frames transmit control information, and data frames are the TDMA time slots allotted to the nodes involved in data transfer. A positive shift in resynchronization is defined as the transmission of a data packet at an absolute time later than the slot in the current frame structure. Negative shift is defined as advancing the start of a superframe to transmit the data packets earlier that in the start of transmission in the current frame structure.

Resynchronization maintains slot assignment to routes through the node, but shifts the start of the superframe. If the clocks of nodes of partition 1 have to be updated, the superframe can be shifted without loss of data or reconfiguration. However, if the clocks of partition 2 have to be shifted, as shown in Figure , some data frames are lost due to the negative shift. If the policy of positive shift is followed uniformly, the nodes must have the capacity to buffer up to an entire superframe's data packets to start afresh with the new timing, as shown in Figure. Buffering alleviates the problem of data loss on the link whose end-points are being resynchronized, but neighboring links may suffer collisions when they follow different clocks.

Hence, as the resynchronization proceeds radially from the new leader, there is

data loss along the head of the resynchronization wave. This remains for a time period proportional to the time taken for the Leader Announcement packet to propagate from the leader to the farthest node, which in turn depends on the diameter of the network, until the entire network is resynchronized. Also, different methods for transmitting the synchronization information have been studied. Out-of-band synchronization uses a separate control channel for sending claim and beacon packets. Collisions are reduced to a great extent for the control packets. However, the available bandwidth for data transmission is reduced, and the cost of the mobile nodes increases because of the need for an additional radio interface. In in-band synchronization, control information for synchronization shares the same channel with the data packets, as shown in Figure .

80

This leads to a greater number of collisions, but avoids an additional channel or bandwidth reservation.

Piggy-backing can be used to reduce explicit control packets. Control information is piggy-backed onto outgoing data packets, as in Figure 12.21 (b). This involves very low overhead with each packet and leads to considerable bandwidth saving. A control packet carrying the synchronization information is originated only if there are no data packets to be sent from the node. The scheme can also be applied with piggybacking on the link-level acknowledgments. In sensor networks, data usually flows from all sensors to the monitor, which is a fixed node with greater computing and power resources than the sensors. If the monitor is forced to be the leader, the synchronization information moves in the reverse direction, that is, along the link-level acknowledgments sent by the nodes for each hop of the data packets, as shown in Figure. Using simulation studies, this has been observed to be the most efficient mechanism. Figure . Shifting of frames on resynchronization.

Figure . In-band signaling.

81

4. Explain about Transport Layer Issues of WSN in detail. Transport Layer Issues

The major issue in transport layer protocols for sensor networks is the provision of reliable data delivery. This assumes special significance in the design of general-purpose sensor networks, where groups of nodes may need to be reconfigured or reprogrammed to suit an evolving application. This may require disseminating a code segment to some nodes, where loss of even a single line of code would render the retasking operation a failure. In a reliable, robust, scalable, and customizable transport protocol, pump slowly fetch quickly (PSFQ), is proposed. The key concept behind the protocol is that a source node distributes data at a slow rate (pump slowly), and a receiver node which experiences data loss retrieves the missing data from immediate neighbors quickly (fetch quickly). PSFQ assumes that data loss is due to poor link conditions rather than traffic congestion. It proposes a hop-by-hop error recovery scheme, rather than holding only the destination node responsible for error detection. The overhead of requiring intermediate nodes to keep track of forwarded data is justified in sensor networks, because most transmissions are intended for groups of sensors, so intermediate nodes are also intended receivers.

PSFQ consists of three functions: message relaying (pump), error recovery (fetch), and selective status reporting (report). The pump operation disseminates data to all target nodes, performs flow control, and localizes loss by ensuring caching at intermediate nodes. Hence, the errors on one link are rectified locally without propagating them down the entire path. When a receiver detects gaps in the received sequence numbers, a loss is indicated, and it goes into fetch mode. It requests a retransmission from neighbor nodes. An attempt is made to aggregate losses, that is, many message losses are batched into a single fetch operation, which is especially appropriate for bursty losses. PSFQ supports a report operation to provide feedback on data delivery status to the source. The farthest target node initiates its report on the reverse path of data, and all intermediate nodes append their reports to the same. Hence, PSFQ ensures that data segments are delivered to all intended receivers in a scalable and reliable manner, even in an environment where the radio link quality is poor. It has been observed that the ratio between the fetch and pump rates should be around 5 for maximum effectiveness.

82

A recent protocol, event-to-sink reliable transport (ESRT) [34], studies a new perspective on reliability in sensor networks. It defines event-to-sink reliability in place of the traditional end-to-end reliability provided by the transport layer, that is, data about the event is to be carried reliably to the sink, with minimum energy expenditure. The sink is required to track reliably only the collective report about an event and not individual reports from each sensor. This enables a relaxation in stringent end-to-end reliability for each flow.

The salient features of ESRT are its self-configuring capability, energy

awareness, and congestion control. ESRT defines the term observed reliability as the number of packets that are routed from event to sink, and required reliability as the desired number of such packets for the event to be successfully tracked. If the observed reliability of an event falls below the requirement, ESRT increases the reporting frequency. On the other hand, if the reliability level required has been exceeded, ESRT decreases the reporting frequency in order to conserve energy. The frequency at which sensors must send their reports is conveyed to them through broadcasts from the sink, after appropriate calculations, so that the required reliability is achieved. Congestion control is achieved by monitoring buffer levels at forwarding sensors. Reliability in the reverse direction, from sink to sensors,

The different kinds of reliability required in this direction are listed. On one hand, small queries are sent in a single packet, whereas software that needs to be updated in the sensors may be sent across multiple packets. Accordingly, reliability should be ensured for single or multiple packets, depending on the content. Further classification is based on the intended set of receivers. A message may need to be sent to all sensors of the network, or to all within a subarea (as in a location-based query), or maybe to a subset of sensors which, among themselves, covers a certain area. In the last case, not all sensors in the area need to receive the message, but only a small subset, the union of whose coverage areas adds up to the required area, needs to reliably receive the message. One of the ways to ensure any of these forms of reliability is to use some nodes as recovery servers, which retransmit the message to sensors which did not receive it. Security

Sensor networks, based on an inherently broadcast wireless medium, are vulnerable to a variety of attacks. Security is of prime importance in sensor networks because nodes assume a large amount of trust among themselves during data aggregation and event detection. From a set of sensor nodes in a given locality, only one final aggregated message may be sent to the BS, so it is necessary to ensure that communication links are secure for data exchange.

Routing protocols can be affected by spoofing or altering the routing information

exchanged between nodes. This can lead to errors in routing, higher latency, or even partitioning of the network. The Sybil attack [37] occurs when a single node presents itself as multiple entities to the network. This can affect the fault tolerance of the network and mislead geographic routing algorithms. Encryption and authentication using a globally shared key can prevent these attacks caused by an outsider trying to corrupt the messages in the network. A selective forwarding attack is a situation when certain nodes do not forward many of the messages they receive. The sensor networks depend

83

on repeated forwarding by broadcast for messages to propagate throughout the network. Sinkhole attacks are those which make a malicious node seem very favorable to the routing algorithm so that most data is routed through it. This node then performs selective forwarding, or acts as a "sink." Sensor networks are especially vulnerable to sinkhole attacks because most traffic is toward the BS.

So, providing a single "favorable" route is likely to influence a large number of nodes to route their data through the malicious node. The wormhole attack lures traffic through a very long path by giving false information to the nodes about the distance between them. This increases latency by avoiding some other possible shorter paths. Wormhole and sinkhole attacks are difficult to counter because routing information supplied by a node is difficult to verify. However, geographic routing protocols are not affected by these attacks since the routes are considered on demand using the location coordinates, so false distances can be verified. Hello flood attacks can be caused by a node which broadcasts a Hello packet with very high power, so that a large number of nodes even far away in the network choose it as the parent. All messages now need to be routed multi-hop to this parent, which increases delay. This can be avoided by checking the bidirectionality of a link, so that the nodes ensure that they can reach their parent within one hop. The rest of this section deals with some protocols that have been proposed to improve security in sensor networks. Localized Encryption and Authentication Protocol (LEAP) Localized encryption and authentication protocol (LEAP) [38] is a key management protocol (a protocol to distribute cryptographic keys) for sensor networks based on symmetric key algorithms, that is, the same key is used by sender and receiver.

In a network, requiring every pair of nodes to have a shared key to be used for

communication between them is ideal for security, because an attack on any one node does not compromise the security of other nodes. However, in sensor networks, the neighbors of a node may not be known in advance, hence this sharing of keys must take place after the network is deployed, which will cause a high overhead. Also, sensor networks may employ certain processing optimizations such as a node's deciding not to report an event if it overhears its neighbor reporting the same. Such optimizations will be precluded by the usage of a separate key for each neighboring pair. On the other hand, having a common key for all nodes in the network has lower overhead, but compromise of any node affects the entire system. LEAP uses different keying mechanisms for different packets depending on their security requirements. For instance, routing information, which is usually in broadcast mode, does not require confidentiality, whereas aggregated data sent to the BS must be confidential. Every sensor node maintains four types of keys: an individual key which it shares with the BS; a group key shared with all nodes of the network and the BS; a cluster key shared between a node and its neighbors; and a pair wise shared key with each of its neighbors.

The individual key is preloaded into the node before deployment, and is used for

transmission of any special information between the BS and the node, such as exclusive instructions to a node, or report from a node to BS about the abnormal behavior of a neighboring node. It is assumed that the time required to attack a node is greater than the network establishment time, during which a node can detect all its

84

immediate neighbors. A common initial key is loaded into each node before deployment. Each node derives a master key which depends on the common key and its unique identifier. N des then exchange Hello messages, which are authenticated by the receivers (since the common key and identifier are known, the master key of the neighbor can be computed). The nodes then compute a shared key based on their master keys. The common key is erased in all nodes after the establishment, and by assumption, no node has been compromised up to this point. Since no adversary can get the common key, it is impossible to inject false data or decrypt the earlier exchange messages. Also, no node can later forge the master key of any other node. In this way, pairwise shared keys are established between all immediate neighbors. The cluster key is established by a node after the pairwise key establishment. A node generates a cluster key and sends it encrypted to each neighbor with its pairwise shared key. The group key can be preloaded, but it should be updated once any compromised node is detected. This could be done, in a naive way, by the BS's sending the new group key to ach node using its individual key, or on a hop-by-hop basis using cluster keys. Other sophisticated algorithms have been proposed for the same. Further, the authors of [38] have proposed methods for establishing shared keys between multi-hop neighbors.

Intrusion Tolerant Routing in Wireless Sensor Networks (INSENS) Intrusion

tolerant routing in wireless sensor networks (INSENS) [39] adopts a routing-based approach to security in sensor networks. It constructs routing tables at each node, bypassing malicious nodes in the network. The protocol cannot totally rule out attack on nodes, but it minimizes the damage caused to the network. The computation, communication, storage, and bandwidth requirements at nodes are reduced, but at the cost of greater computation and communication at the BS. To prevent DoS attacks, individual nodes are not allowed to broadcast to the entire network. Only the BS is allowed to broadcast, and no individual nodes can masquerade as the BS, since it is authenticated using one-way hash functions (i.e., a hash function whose inverse is not easy to obtain). Control information pertaining to routing must be authenticated by the BS in order to prevent injection of false routing data. The BS computes and disseminates routing tables, since it does not face the computation and energy constraints that the nodes do. Even if an intruder takes over a node and does not forward packets, INSENS uses redundant multipath routing, so that the destination can still be reached without passing through the malicious node. INSENS has two phases: route discovery and data forwarding. During the route discovery phase, the BS sends a request message to all nodes in the network by multi-hop forwarding (not using its broadcast). Any node receiving a request message records the identity of the sender and sends the message to all its immediate neighbors if it has not already done so. Subsequent request messages are used to identify the senders as neighbors, but repeated flooding is not performed. The nodes respond with their local topology by sending feedback messages.

The integrity of the messages is protected using encryption by a shared key

mechanism. A malicious node can inflict damage only by not forwarding packets, but the messages are sent through different neighbors, so it is likely that it reaches a node by at least one path. Hence, the effect of malicious nodes is not totally eliminated, but it is restricted to only a few downstream nodes in the worst case. Malicious nodes may also send spurious messages and cause battery drain for a few upstream nodes. Finally, the BS calculates forwarding tables for all nodes, with two independent paths for

85

each node, and sends them to the nodes. The second phase of data forwarding takes place based on the forwarding tables computed by the BS. Security Protocols for Sensor Networks (SPINS)

Security protocols for sensor networks (SPINS) consists of a suite of security

protocols that are optimized for highly resource-constrained sensor networks. SPINS consists of two main modules: sensor network encryption protocol (SNEP) and a micro-version of timed, efficient, streaming, loss-tolerant authentication protocol (μTESLA). SNEP provides data authentication, protection from replay attacks, and semantic security, all with low communication overhead of eight bytes per message. Semantic security means that an adversary cannot get any idea about the plaintext even by seeing multiple encrypted versions of the same plaintext. Encryption of the plaintext uses a shared counter (shared between sender and receiver). Hence, the same message is encrypted differently at different instances in time. Message integrity and confidentiality are maintained using a message authentication code (MAC). This is similar to a checksum derived by applying an authentication scheme with a secret shared key to the message. The message can be decrypted only if the same shared key is present. The message also carries the counter value at the instance of transmission (like a time-stamp), to protect against replay attacks. μTESLA ensures an authenticated broadcast, that is, nodes which receive a packet can be assured of its sender's identity. It requires a loose time synchronization between BS and nodes, with an upper bound on maximum synchronization error. The MAC keys are derived from a chain of keys, obtained by applying a one-way function F (a one-way function is one whose inverse is not easily computable). All nodes have an initial key K0 , which is some key in the key-chain. The relationship between keys proceeds as K0 = F(K1 ), K1 = F(K2 ), and, in general, Ki = F(Ki+ 1 ). Given K0 , K1 , ..., Ki , it is not possible to compute Ki+ 1 . The key to be used changes periodically, and since nodes are synchronized to a common time within a bounded error, they can detect which key is to be used to encrypt/decrypt a packet at any time instant.

The BS periodically discloses the next verification key to all the nodes and this

period is known to all nodes. There is also a specified lag of certain intervals between the usage of a key for encryption and its disclosure to all the receivers. When the BS transmits a packet, it uses a MAC key which is still secret (not yet disclosed). The nodes which receive this packet buffer it until the appropriate verification key is disclosed. But, as soon as a packet is received, the MAC is checked to ensure that the key used in the MAC has not yet been disclosed, which implies that only the BS which knows that yet undisclosed key could have sent the packet. The packets are decrypted once the key-disclosure packet is received from the BS. If one of the key-disclosure packets is missed, the data packets are buffered till the next time interval, and then authenticated.

For instance, suppose the disclosure packet of Kjdoes not reach a node; it waits

till it receives Kj+ 1 , then computes Kj = F(Kj+ 1 ) and decrypts the packets received in the previous time interval. Real-Time Communication

Support for real-time communication is often essential in sensor networks which are used for surveillance or safety-critical systems. The communication delay between sensing an intrusion and taking appropriate action greatly affects the quality of tracking

86

provided by a surveillance system. Similarly, in a nuclear power plant, the detection of an abnormality in temperature or pressure must be conveyed in real-time to the control system in order to take immediate action. Hence, delay guarantees on routing would be extremely useful for such systems. Two protocols which support real-time communication in sensor networks — SPEED and RAP — are discussed in this section. SPEED A stateless protocol, SPEED, which supports real-time communication in sensor networks, has been proposed in [41]. SPEED is a localized algorithm which provides real-time unicast, real-time area-multicast (multicast to all nodes in a particular region), and real-time anycast support for packet transmission.

SPEED has minimal overheads, as it does not require routing tables. It is

compatible with best-effort MAC layer, not requiring any special MAC support. It also distributes traffic and load equally across the network using nondeterministic forwarding. The SPEED protocol requires periodic beacon transmissions between neighbors. It also uses two specific on-demand beacons for delay estimation and congestion (back-pressure) detection. These are used to adapt to changes in the network. The load at a node is approximated using single-hop delay. The measurement is made using data packets which pass by a node, instead of separate probe packets. This minimizes the overhead. Nodes also respond using the delay estimation beacon to inform neighbors of the estimated delay.

Routing of packets is performed by stateless non-deterministic geographic

forwarding (SNGF). Using geographic information, packets are forwarded only to the nodes which are closer to the destination. Among the eligible closer nodes, the ones which have least estimated delay have a higher probability of being chosen as an intermediate node. If there are no nodes that satisfy the delay constraint, the packet is dropped .SPEED uses a neighbor feedback loop (NFL) to maintain the estimated delay fairly constant, so that frequent updates of delay estimates are not required. When a packet has to be dropped, that is, there is no path which can meet the delay constraint, the sending rate to the downstream nodes (nodes which are closer to the receiver) is reduced to avoid congestion, thereby maintaining the delay. The NFL issues a back-pressure beacon indicating the average delay. The increased delay is noted, and SNGF accordingly reduces the probability of selecting the congested downstream nodes for routing, until eventually the congestion eases out and delay is reduced. This can continue recursively, propagating the back-pressure from downstream to upstream nodes (nodes which are closer to the sender), to relieve congestion in a hotspot. Many geographic routing algorithms may encounter a situation when there is no node close to the destination to forward a packet. This is called a "void." SPEED uses a void-avoidance technique by issuing a back-pressure beacon with estimated delay as infinite. This will trigger a search for alternative paths. Hence, if there exists any path to a destination satisfying the delay constraint, it will be detected by SPEED. The protocol provides support for real-time communication over sensor networks by providing guarantees on the maximum delay. RAP

RAP provides APIs for applications to address their queries. An application layer program in theBS can specify the kind of event information required, the area to which the query is addressed, and the deadline within which information is required. The

87

underlying layers of RAP ensure that the query is sent to all nodes in the specified area, and the results are sent back to the BS.

The protocol stack of RAP consists of location addressed protocol (LAP) in the

transport layer, velocity monotonic scheduling (VMS) as the geographic routing protocol, and a contention-based MAC scheme that supports prioritization. LAP is a connectionless transport layer protocol which uses location to address nodes instead of a unique addressing scheme such as IP address. It supports three kinds of communication: unicast, area multicast, and area anycast. VMS is based on the concept of packet-requested velocity, which reflects both the timing and the distance constraints.

Hence, requested velocity is a measure of the urgency of the packet. If a packet

can travel at its requested velocity, that is, can cover the required distance within a specified time, then it can meet its deadline. VMS gives higher priority to packets which have requested higher velocities. The velocity of a packet is calculated as the ratio of the geographic distance between sender and receiver, to the deadline. Dynamic VMS recalculates the velocity at each intermediate node, so that a packet which has been slower than its requested velocity until then can be given higher priority. This is mapped onto a MAC layer priority, which is handled by the contention-based MAC layer. The protocol hence provides convenient services for application layer programs that require real-time support. 5. Explain in detail about WSN Routing & OLSR(Optimal Link State Routing)

Protocol.[Nov/Dec’15]

(Ans: Refer 6.4 and 6.5 in Text Book)

Optimized Link State Routing

The optimized link state routing (OLSR) protocol is a proactive routing protocol that employs an efficient link state packet forwarding mechanism called multipoint relaying. This protocol optimizes the pure link state routing protocol. Optimizations are done in two ways: by reducing the size of the control packets and by reducing the number of links that are used for forwarding the link state packets. The reduction in the size of link state packets is made by declaring only a subset of the links in the link state updates. This subset of links or neighbors that are designated for link state updates and are assigned the responsibility of packet forwarding are called multipoint relays. The optimization by the use of multipoint relaying facilitates periodic link state updates.

The link state update mechanism does not generate any other control packet

when a link breaks or when a link is newly added. The link state update optimization achieves higher efficiency when operating in highly dense networks. Figure 7.30 (a) shows the number of message transmissions required when the typical flooding-based approach is employed. In this case, the number of message transmissions is approximately equal to the number of nodes that constitute the network. The set consisting of nodes that are multipoint relays is referred to as MPRset.

88

Each node (say, P) in the network selects an MPRset that processes and forwards every link state packet that node P originates. The neighbor nodes that do not belong to the MPRset process the link state packets originated by node P but do not forward them. Similarly, each node maintains a subset of neighbors called MPR selectors, which is nothing but the set of neighbors that have selected the node as a multipoint relay. A node forwards packets that are received from nodes belonging to its MPRSelector set.

The members of both MPRset and MPRSelectors keep changing over time. The

members of the MPRsetof a node are selected in such a manner that every node in the node's two-hop neighborhood has a bidirectional link with the node. The selection of nodes that constitute the MPRset significantly affects the performance of OLSR because a node calculates routes to all destinations only through the members of its MPRset. Every node periodically broadcasts its MPRSelector set to nodes in its immediate neighborhood. In order to decide on the membership of the nodes in the MPRset, a node periodically sends Hello messages that contain the list of neighbors with which the node has bidirectional links and the list of neighbors whose transmissions were received in the recent past but with whom bidirectional links have not yet been confirmed. The nodes that receive this Hello packet update their own two-hop topology tables. The selection of multipoint relays is also indicated in the Hellopacket.

A data structure called neighbor table is used to store the list of neighbors, the

two-hop neighbors, and the status of neighbor nodes. The neighbor nodes can be in one of the three possible link status states, that is, unidirectional, bidirectional, and multipoint relay. In order to remove the stale entries from the neighbor table, every entry has an associated timeout value, which, when expired, removes the table entry. Similarly a sequence number is attached with the MPRsetwhich gets incremented with every new MPRset. Figure . An example selection of MPRset in OLSR.

89

The MPRset need not be optimal, and during initialization of the network it may be same as the neighbor set. The smaller the number of nodes in the MPRset, the higher the efficiency of protocol compared to link state routing. Every node periodically originates topology control (TC) packets that contain topology information with which the routing table is updated. These TC packets contain the MPRSelectorset of every node and are flooded throughout the network using the multipoint relaying mechanism. Every node in the network receives several such TC packets from different nodes, and by using the information contained in the TC packets, the topology table is built. A TC message may be originated by a node earlier than its regular period if there is a change in the MPRSelector set after the previous transmission and a minimal time has elapsed after that. An entry in the topology table contains a destination node which is the MPRSelector and a last-hop node to that destination, which is the node that originates the TC packet. Hence, the routing table maintains routes for all other nodes in the network. Selection of Multipoint Relay Nodes Figure (b) shows the forwarding of TC packets using the MPRsetof node 4. In this example, node 4 selects the nodes 2, 3, 10, and 12 as members of its MPRset. Forwarding by these nodes makes the TCpackets reach all nodes within the transmitting node's two-hop local topology. The selection of the optimal MPRsetis NP-complete]. In a heuristic has been proposed for selecting the MPRset.The notations used in this heuristic are as follows: Ni(x) refers to the ith hop neighbor set of node x and MPR(x) refers to the MPRsetof node x.

90

1. MPR(x) ← Ø/* Initializing empty MPRset*/ 2. MPR(x) ← { Those nodes that belong to N1(x) and which are the only neighbors of nodes in N2(x) } 3. While there exists some node in N2(x) which is not covered by MPR(x)

1. For each node in N1(x), which is not in MPR(x), compute the maximum number of nodes that it covers among the uncovered nodes in the set N2(x). 2. Add to MPR(x) the node belonging to N1(x), for which this number is maximum.

A node updates its MPRset whenever it detects a new bidirectional link in its neighborhood or in its two-hop topology, or a bidirectional link gets broken in its neighborhood.

Route Computation Before packet transmission, route has to be established

between the sender and the recener nodes. The Dijkstra's shortest path algorithm is

used for finding route between nodes. The route calculation procedure can be initiated

when a change is found in either of the following: the link set, the neighbor set, the two-

hop neighbor set, the topology set, or the MPRset.

Routing table can be computed from neighbor table and topology table. The

shortest path is maintained in the routing table. When a node wants to communicate

with other node, it first checks the routing table to identify route between sender and the

receiver nodes. Once it found route, then handshaking procedure will be carried out

using RTS/CTS mechanism. After that, actual data transmission will be taken place.

6. Discuss in detail about Localization.[May/June’15&’16][Nov/Dec’15].

(Nov/Dec 2016)

Localization system is a major issue of WSNs. The key responsibility of each

sensor node is to identify the changes in the particular environment or area. Certain

applications require the information received from sensor nodes with accurate

positional information of the event occurred. Sometimes. the sensor nodes may he

deployed in inaccessible areas like disaster relief areas and forests. in this case,

determining the actual position of sensor nodes may not be a feasible task. So efficient

localization systems are required in order to provide positional information of the

nodes.

91

The location information of sensors has to be considered during aggregation of

sensed data. This implies each node should know its location and couple its location

information with the data in the messages it sends. A low-power, inexpensive, and

reasonably accurate mechanism is needed for location discovery.

Global positioning system (GPS)

A global positioning system (GPS) is not always feasible because it cannot reach nodes

in dense foliage or indoors. It also consumes high power and makes sensor nodes

bulkier. Two basic mechanisms of location discovery are now described.

Indoor Localization

Indoor localization techniques use a fixed infrastructure to estimate the location of

sensor nodes. Fixed beacon nodes are strategically placed in the field of observation,

typically indoors, such as within a building. The randomly distributed sensors receive

beacon signals from the beacon nodes and measure the signal strength, angle of

arrival, and time difference between the arrival of different beacon signals.

Sensor Network Localization

In situations where there is no fixed infrastructure available and prior

measurements are not possible, some of the sensor nodes themselves act as beacons.

They have their location information, using GPS, and these send periodic beacons to

other nodes. In the case of communication using RF signals, the received signal

strength indicator (RSSI) can be used to estimate the distance,

. These are called multi-lateration (ML) techniques.

Some simple ML techniques are described in what follows

• Atomic ML

• Iterative ML

• Collaborative ML

If a node receives three beacons, it can determine its position by a mechanism similar

to GPS.

92

Atomic multi-lateration.

Iterative ML: Some nodes may not be in the direct range of three beacons.

Once a node estimates its location, it sends out a beacon, which enables some other

nodes to now receive at least three beacons. Iteratively, all nodes in the network can

estimate their location.

.

Figure Iterative multi-lateration.

•

• Collaborative ML: When two or more nodes cannot receive at least three beacons

each, they collaborate with each other.Hence, by solving a set of simultaneous

quadratic equations, the positions of A and B can be determined.

93

Figure Collaborative multi-lateration.

Absolute Localization

Absolute localization is one of the GPS-based localizations. In general, GPS

based localization requires that the sensor nodes must be equipped with GPS receiver.

In absolute localization method, the sensor nodes equipped with GPS receiver are used

nodes. An absolute coordinate system will be defined by these reference nodes.

coordinates can be obtained from relative coordinate system by applying simple linear

transformation and some reference nodes (beacon nodes).

Relative Localization

The indirect approach of localization is termed as relative localization. Since the

location of sensor nodes can be determined based on the relative position of other

sensor nodes, this localization method is called as indirect approach. The relative

localization is used to find out the distance between nodes. Its distance is relative to

some reference nodes also called as beacon nodes.

In relative localization, a relative coordinate system has to be defined by using

some reference nodes. The positions of sensors are determined using inter-sensor

measurements such as distance, time difference of arrival, angle of arrival and

connectivity that are relative to other sensors.

In this method, there are some sensor nodes equipped with GPS receivers. Now

tiles' nodes are capable of calculating its position and these positional information ID

other nodes (which may not have GPS receiver) as beacon signals. The sensor nodes

94

which receives this information will compute its location with respect to the positional

information which had been received through beacon message. will be broadcasted.

DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING …old.scteng.co.in/documents/cselms.pdf ·...

Documents

Transcript of DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING …old.scteng.co.in/documents/cselms.pdf ·...