International Institute of Information Technology, Pune* Introduction to Mobile Ad Hoc Networks (MANETS) Prof. Ravindra P. Joshi

International Institute of Information Technology, Pune

International Institute of Information Technology, Pune*Agenda Introduction

Ad Hoc wireless networks

Challenges for Ad Hoc networks

Media Access and related issues

Routing protocols for Ad Hoc networks

Comparison of few routing protocols

Conclusion

International Institute of Information Technology, Pune

International Institute of Information Technology, Pune*Introduction Mobile Ad Hoc networks and Wireless sensor networks are the two special categories of wireless networks that are attracting attention of industry and academia for quite some time.

Low cost, low power, low bandwidth, multi-functional networks

Design and implementation issues

New algorithms for media access and routing are being designed to optimize the performance

International Institute of Information Technology, Pune

International Institute of Information Technology, Pune*Introduction Many wireless networks of today need an infrastructure network, which not only provides access to other networks, but also include forwarding functions, medium access control (MAC) etc. In these infrastructure-based networks, communication typically takes place only between the wireless nodes and the access point but not directly between the wireless nodes. MANETS use multi-hop radio relaying and are capable of operating without the support of any fixed infrastructure.

International Institute of Information Technology, Pune

International Institute of Information Technology, Pune*Infrastructure based and Ad Hoc networks

International Institute of Information Technology, Pune

* Vehicular Ad Hoc networks (VANETs) are a form of MANETs used for communication among vehicles and between vehicles and roadside equipment.

Intelligent vehicular ad hoc network (InVANET) is a kind of Intelligence in vehicle(s) which provide multiple autonomic intelligent solutions to make automotive vehicles to behave in intelligent manner during vehicle- to-vehicle collisions, accidents etc.

InVANET uses WiFi IEEE 802.11 b/802.11g/802.11p and WiMAX (IEEE 802.16) for providing easy, accurate, effective communication between multiple vehicles with dynamic mobility.Introduction to VANETs

*Introduction to VANETs Effective measures to track the automotive vehicles, media download /upload, conference between vehicles are also preferred.

InVANET can also be applied for artillery vehicles during warfare, battlefield, and peace-time operations.

Mesh networking in mobile applications have been demonstrated in multiple military scenarios.

*Features of Ad Hoc networks A mobile Ad hoc network (MANET) is a type of wireless network that is self-configuring network of mobile nodes connected by wireless links and forms an arbitrary topology.

Nodes are free to move randomly and organize themselves arbitrarily; thus, the network topology may change unpredictably.

Such a network may operate in a standalone fashion, or may be connected to the Internet.

Quick deployment, multi-hop topologies

Short lived networks

* Cellular networks:

Cellular networks are classified as the infrastructure dependent networks. The path set-up for a call between two nodes is completed through the base station in a centralized manner.

These networks offer single hop wireless links and guaranteed bandwidth for real time (voice) traffic.

This simplifies routing and resource management, since the routing decisions are made centrally at the base station with more information about the destination node.Comparison with cellular networks

*Cellular NetworksSwitching center + GatewayCEDABPath from C to E

* Ad Hoc wireless networks:

Ad hoc wireless networks utilize multi-hop radio relaying and operate without support of any fixed infrastructure. This makes the routing complex compared to cellular networks.

Nodes must communicate to each other regarding information about other nodes. A node can transmit and receive data, as well as act as a router for routing packets from other nodes.

They do not offer guaranteed bandwidth and hence not suitable for real time (voice) applications.Comparison with cellular networks

*Ad Hoc wireless networksCEDBAPath from C to E

*Applications of Ad Hoc wireless networks Military applications:

Communication between soldiers or tanks in a battlefield.

Reliable, efficient, secure communication is main concern along with support for multicast routing.

Collaborative & Distributed Computing:

Communication and file transfer between people in a conference (multicast transmission)Devices could be laptops with add-on wireless interface cards, PDAs, mobile devices with high processing power.

Emergency operations:

Search and rescue operationsCrowd controlEarthquake hit areas

*Wireless mesh networks Wireless mesh networks are Ad Hoc networks that are formed to provide an alternative communication infrastructure for mobile/fixed users, without the spectrum reuse constraints.

Mesh topology provides many alternative paths for a data transfer session.

Quick reconfiguration of a path is possible, in case the existing path fails or node failure occurs.

These networks provide most economical data transfer capability coupled with the freedom of mobility.

Support high data rates, quick and low cost of deployment, high availability and low cost per bit.

*Wireless mesh network deployments Infrastructure can be built in the form of small radio relaying devices fixed on top of the houses in a residential zone.

Possible deployment includes small residential building complexes (where a broadband Internet connectivity is required)

Highways (where a communication facility for moving automobiles is required)

Business zones (where an alternative communication system to cellular networks is required)

University campus (where inexpensive campus wide network coverage is required).

*Wireless mesh network (residential zone)

*Wireless mesh networks Wireless mesh networks operate at the license free ISM bands around 2.4 GHz and 5 GHz, depending on the technology used for the physical and MAC layer communication, data rates of 2 Mbps to 60 Mbps can be supported.

Incremental or partial deployment can also be done and hence the deployment time can be shortened.

When deployed on highways, truck driver can utilize location discovery services, hence spotting his location on an updated digital map is possible.

*Wireless mesh network (on a highway)

*Issues in Ad Hoc wireless networks Medium access scheme

Routing

Multicasting

Transport layer protocol

Pricing scheme

Quality of Service (QoS) provisioning

Self-organization

Security

Energy management

Addressing and Service discovery

Scalability

Deployment considerations

*MAC layer issues Medium access scheme:

Performance of any wireless network is related to the MAC layer protocol and following are major considerations,

Distributed operation:

Polling may be required at regular intervals, but with minimum overheads

Synchronization:

Time synchronization is required, but with optimum usage of bandwidth and battery power.

Hidden node and exposed node problems:

MAC layer protocol should take care of these problems

* Location dependent contention:

Load on the wireless channel varies with the number of nodes present in a given geographical region. Good routing protocol should avoid channel contention at high loads.

Resource constraints: Constraints such as computing power, battery power, buffer storage etc. also limit the capability of a routing protocol.

Minimum route acquisition delay: This delay may vary as per size of the network and network load.

Quick route reconfiguration:

Loop-free routing: Due to movement of nodes, transient loops may get formedMAC layer and routing issues

*Challenges in routing Issues to be considered for while designing routing protocols for Ad Hoc networks:

Mobility of nodesFrequent path breaks Disruption due to movement of nodes

Resource constraintsBandwidth constraints Less control overheads Battery life and processing power

Error prone channelShared broadcast radio channel, interference, fading

Hidden & Exposed terminal problems

*Issues related to multicastingThe challenges for multicasting are,

Robustness:

Multicasting protocol should be able to recover and reconfigure quickly from the potential mobility induced link breaks, thus making it suitable for dynamic environments.

Efficiency: Should have minimum number of transmissions to deliver a packet to all group members.

Control overhead and Quality of Service:

Efficient group management:

Accepting the session members and maintaining the connectivity between them until the session expires.

Scalability and Security:

*Other challenges Self organization:

Ad Hoc networks should organize and maintain the network by itself. The major activities in this are neighbor discovery, transmitting beacons to detect the neighbor activities, topology organization and re-organization.

Security:

For military networks, this is an important aspect. Lack of central control and shared wireless medium makes them more vulnerable to attacks. Main security threats are Denial of Service, Resource consumption, Information disclosure and Interference.

* Scalability:

Due to the constraints mentioned earlier, scalability will be limited for Ad Hoc networks.

Deployment considerations:

Low cost of deployment

Incremental deployment

Short deployment time

Ability to Reconfigure

Area of coverage

Operational integration with other infrastructure

Choice of protocolsOther challenges

*Classification of MAC layer protocols

*Classification of MAC protocols Classification of MAC protocols:

MAC protocols can be classified into various categories based on various criteria such as initiation approach, time synchronization and reservation approaches.

Following are the there basic types of classification:

Contention based protocols

Contention based protocols with reservation mechanisms

Contention based protocols with scheduling mechanisms

*MAC protocolsContention based protocolsContention based protocols with reservation mechanisms Contention based protocols with scheduling mechanismsOther MAC protocolsSender InitiatedprotocolsReceiver Initiatedprotocols Single channelprotocols Multi channelprotocolsMACAW

FAMABTMA

DBTMA

ICSMARI -BTMA

MACA-BI

MARCHD -PRMA

CATA

HRMA

SRMA/PA

FPRPMACA/PR

RTMACDPS

DWOP

DLPSProtocolsusing Directionalantennas

MMAC

MCSMA

PCM

RBARSynchronous protocolsAsynchronous protocols

*Contention based protocols Contention based protocols:

They follow contention based channel access policyNode does not make any resource reservation.These protocols can not provide any QoS guarantee

They are further divided into,

Sender initiated protocols:

Single channel type: Total bandwidth is available

Multi channel type: Bandwidth is shared among channels Enables several nodes to transmit data using separate channel

Receiver initiated protocols

* Contention based protocols with reservation mechanisms

Bandwidth is reserved, hence they can support QoS

Synchronous protocols:

They require time synchronization among all nodes in the network, so that reservations made by a node are known to other nodes in the neighborhood.

Asynchronous protocols:

These protocols use relative time information for effecting reservations.Contention based protocols

* 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 the 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.

Some scheduling schemes also take into account remaining battery power, while scheduling nodes for access to the channel.Contention based protocols

*Classification of routing protocols

*Classification of Routing ProtocolsThe classification is based on four categories:

1) Routing Information Update Mechanism:

Table driven (proactive):

Destination Sequenced Distance Vector (DSDV)

Wireless Routing Protocol (WRP)

Optimized Link State Routing (OLSR)

Source Tree Adaptive Routing (STAR) protocol

Cluster-head Gateway Switch Routing (CGSR) Protocol

*Classification of Routing Protocols On-demand (reactive):

Dynamic Source Routing Protocol (DSR)

Ad Hoc On-demand Distance Vector (AODV)

Hybrid Routing Protocols:

Combine the advantages of above

E.g. Core Extraction Distributed Ad Hoc Routing (CEDAR) Protocol

*2) Based on the Routing Topology:

Flat topology routing protocols

Dynamic Source Routing (DSR) protocol

Ad Hoc On-demand Distance Vector

Flow Oriented Routing Protocol (FORP)Hierarchical topology routing protocols

Cluster-head Gateway Switch Routing (CGSR) Protocol

Fisheye State Routing (FSR) Protocol

Hierarchical State Routing (HSR) ProtocolClassification of Routing Protocols

*3) Based on the utilization of specific resources:

Power aware routing

Protocols under this category aim at minimizing consumption of battery power, either locally or globally. Routing decisions are based on this objective.

E.g Power Aware Routing (PAR) protocolGeographical Information assisted routing

Protocols under this category improve the routing performance and reduce the control overheads by efficiently using geographical information available.

E.g. Location Aided Routing (LAR) protocolClassification of Routing Protocols

*Table driven (proactive) routing protocol

Destination Sequenced Distance Vector (DSDV)

*Table Driven Routing Protocols Destination Sequenced Distance Vector Routing (DSDV) Protocol

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.

It incorporates table updates with increasing sequence number tags to prevent routing loops.

Routes to all destinations are readily available at every node at all the times. Tables are exchanged between the neighbours at regular intervals to keep an up-to-date view of the network topology.

*Network topology165101114151224813379Source nodeDestination node

*Destination Sequenced Distance Vector (DSDV) Routing Protocol Advantages:

Availability of routes to all destinations means less delay in the route set up process.

Mechanism of incremental updates with sequence number tags makes the existing wired network protocols adaptable to Ad Hoc networks.

Disadvantages:

Updates due to broken links are propagated to the whole network, hence more control overheads.

Even a small network with high mobility of nodes, or a large network with low mobility can choke the network.

* Dynamic Source Routing Protocol (DSR)

Ad Hoc On-demand Distance Vector (AODV) On-demand (reactive) routing protocols

*Dynamic Source Routing (DSR) Protocol Dynamic Source Routing (DSR) protocol is an on- demand protocol designed to restrict the bandwidth consumed by periodic update packets in the table- driven approach.

DSR does not require any periodic Hello packets (beacons).

The route to the destination is established by flooding the RouteRequest packets in the network. The destination node (upon receiving the RouteRequest packet) responds by sending a RouteReply packet back to the source, which carries the route information through which the packet has traversed.

*Dynamic Source Routing (DSR) Protocol When the RouteRequest is flooded through the network, each node (upon receiving the RouteRequest packet), rebroadcasts the packet to its neighbours if,

It has not forwarded already If the node is not the destination node If the packets Time to Live (TTL) field is not exceeded

Each RouteRequest carries a sequence number generated by the source node and the path it has traversed.

A node (upon receiving a RouteRequest packet) checks the sequence number on the packet before forwarding it. The packet is forwarded only if it is not a duplicate RouteRequest.

*Dynamic Source Routing (DSR) Protocol The sequence number on the packet is used to prevent loop formations and to avoid multiple transmissions of the same RouteRequest by an immediate node that receives it through multiple paths.

Thus all nodes (except destination node) forward a RouteRequest packet during the route construction phase

A destination node, after receiving the first RouteRequest packet replies to the source node through the reverse path the RouteRequest packet had traversed.

For example, source node-1 initiates the RouteRequest packet to obtain the path to the destination node-15.

*Route Establishment in DSR165101114151224813379Path-1: 1-2-3-7-9-13-15Path-2: 1-5-4-12-15Path-3: 1-6-10-11-14-15RouteRequestRouteReplyNetwork linkSource IDDestination ID

*Advantages of DSR protocolAdvantages:

No periodic updates required, saving of network bandwidth

Route is established only when it is required.

Control overhead is reduced since intermediate nodes can use their cache information effectively

*Disadvantages: Route construction mechanism can not repair the broken link locally. Stale route cache information could result in inconsistencies during route reconstruction phase. Higher connection set-up delay. Performance degrades due to mobility of nodes Routing overhead is proportional to the path length.

Disadvantages of DSR protocol

*Ad Hoc On-demand Routing (AODV) Protocol AODV is also on-demand routing protocol, hence the route is established only when it is required by the source for transmission of data packets.

DSR uses source routing in which a data packet carries the complete path to be traversed, whereas in AODV the source node and intermediate nodes store the next- hop information.

AODV uses destination sequence number (DestSeqNum) to identify the most recent path to the destination. A node updates its path information only if the DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node.

*Ad Hoc On-demand Routing (AODV) Protocol A RouteRequest packet contains,

Source Identifier (SrcID)Destination Identifier (DestID)Destination Sequence Number (DestSeqNum)Broadcast Identifier (BcastID)Time-to-live (TTL) field

DestSeqNum indicates the latest state of the route accepted by the source.

When an intermediate node receives a RouteRequest, it either forwards it or prepares a RouteReply if it has valid route to the destination.

Validity of route is determined by comparing the sequence number at the intermediate node with the DestSeqNum in the RouteRequest packet.

*Ad Hoc On-demand Routing (AODV) Protocol When a node receives a RouteReply packet, information about the previous node from which the packet was received is also stored in order to forward the data packet to this next node as the next hop towards the destination.

Source node-1 initiates the path finding process by originating a RouteRequest to be flooded in the network for destination node-15.

Assume that the DestSeqNum is 3 and source sequence no. is 1. When nodes 2, 5 and 6 receive the RouteRequest packet, they check their routes to the destination.

In case the route is not available, they forward it to their neighbors (nodes 3, 4 and 10)

*Route Establishment in AODV165101114151224813379Path-1: 1-5-10-14-15Path-2: 1-5-4-12-15RouteRequestRouteReplyNetwork linkSource IDDestination IDCashed route 14-15

*Ad Hoc On-demand Routing (AODV) Protocol Advantages:

Since destination sequence number is used, the connection set up delay is less.

Disadvantages:

Intermediate nodes can lead to inconsistent routes if the source sequence number is very old and the intermediate nodes have the higher (but not the latest DestSeqNum), thereby having stale entries.

Multiple RouteReply packets in response to a single RouteRequest packet can lead to heavy control overheads.

*Comparison of characteristics of table driven Vs on-demand routing protocols

*Performance evaluation of routing protocols In this paper, performance of two on-demand reactive routing protocols, namely DSR and AODV is compared with the table driven (proactive) DSDV protocol.

Simulation using Network Simulator (NS-2) is carried out using a network of 50 nodes, which are 100m apart from each other. Transmission range of each node is 250m (default configuration used in NS-2).

*DSDV throughput DSDV has less throughput with higher mobility of nodes due to high overheads in maintaining routing tables and update mechanism of broadcast nature.

*DSR and AODV throughput

* On demand routing protocols such as DSR and AODV perform better under higher mobility conditions.

DSR maintains caching and maintains multiple routes per destination.

AODV uses routing tables and one route per destination and destination sequence numbers.

AODV outperforms DSR with lower mobility. DSR and AODV performance

*Conclusion On demand routing protocols such as DSR and AODV perform better under higher mobility conditions as compared to DSDV.

DSR maintains caching and maintains multiple routes per destination.

AODV outperforms DSR with lower mobility conditions.

DSDV generates more routing load due to its inefficient route update mechanism. Hence on-demand routing protocols work more efficiently than table driven routing protocols.

*Text books/ referencesAd Hoc Wireless Networks Architectures & Protocols (Pearson Education)By C. Siva Ram Murthy and B. S. Manoj

Wireless Sensor Networks (Springer press)

By C. S. Raghavendra, Krishna M. Sivalingam, Toieb Znati

Ad Hoc Networks Technologies & Protocols (Springer Press) Edited by Prashant Mohapatra and Srikanth Krishmurthy

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