Web over Wireless Group An Overview of the Web over Wireless Group Web over Wireless Group UC,...

An Overview of the Web over Wireless GroupWeb over Wireless GroupUC, Berkeley

GroupProf. Pravin Varaiya

Researchers: Dr. Anuj PuriBaris Dundar

Graduate Students:Mustafa ErgenSinem ColeriDuke LeeXuanming DongRahul JainMohit AgarwalAmit Mahajan

Under Graduate Students:Jeff KoYan Li http://wow.eecs.berkeley.edu

Research FocusCellular networksAd Hoc wireless networksSensor networksApplications

Cellular Networks

Current Cellular newtorksGeographical area divided into cellsBase station (BS) in each cellPrimary traffic is voice What will future wireless networks look like?Primary traffic is dataCellular + Wireless LANs

Heterogeneous Wireless Networks802.11 Wireless LANsUpto 50 MbpsUnlicensed spectrumCheap and easy to set upHot spot coverage with wireless LANsMobility between networksApplications

Ad Hoc Wireless NetworksWireless token ringDSDV routingGeographical routingWTPSensor Networks

Wireless Token Ring ProtocolMultiple rings Station with token transmits Deterministic bounds on access time Adjacent rings transmit on different channels Basic operations of join and leave to allow mobility

DSDV - Wireless RoutersCheaper/better performance cellular networksAd Hoc wireless networksInternetWireless Router

Geographical Routing AlgorithmAll nodes know their positions Packet for a destination postion Use geographical information in routingi.e, route to neighbor nearest to the destination

Geographicalnetwork

Transport Layer (WTP)UDP: Connectionless but unreliableTCP: Connection oriented and reliableWTP: Connectionless and reliableUsed by WAP (Wireless application protocol) as a transaction protocol for cell phonesOptimized for wireless links for short messagesDoesnt use congestion controlSmall WTP headersMessage based protocol

Network ArchitecturePhysical LayerData LinkMACNetwork LayerTransport LayerToken ring, bluetooth 802.11, SeedexGeographic routing,DSDV, QOS, TBRF,STARATCP/UDP/WTPMobilityManagementOFDM

Mobility and Internetworking Among NetworksInternetGeographicRoutingSensor Networks802.11TokenRingDSDV

TechnologyWireless Token Ring DSDV routing Geographical routing and WTP Mobile IPFast HandoffMEWLANASensor Networks

WIRELESS TOKEN RING PROTOCOL

The Wireless Token Ring Protocol (WTRP) is a medium access control protocol for wireless networks in mission critical systems. It supports quality of service in terms of bounded latency and reserved bandwidth. The token passing defines the transmission order, and each token is forced to give up the token after a specified amount of time.Each ring has unique ring id based on unique MAC address of one of the stations of the ring. (The station is called the owner of the ring). When owner leaves the ring, another station elects itself to be the owner of the ring.Introduction

Descriptions (Operations)Joining: Stations periodically invite other nodes to join the ring by broadcasting the available resources left in the mediumLeaving: When B wants to leave, it requests A to connect to its successor, C. If A does not have connection with C, then it connects to the next node in terms of the transmission order of the ring.

Descriptions (Management)Ring Recovery Able to recover quickly by keeping information about topology of the ring, recovers from multiple simultaneous faults by taking increasingly drastic actionsToken Recovery Multiple token is deleted using unique priority of token based on generation sequence number and token ring address pair.

WTRP Deliverables

WTRP USER-SPACE

WTRS-WTR Simulator

Performance Analysis

DSDV Routing

DSDV Routing ProtocolBased on Bellman-Ford algorithm Use sequence number to avoid loop-forming and make convergence fastThe sequence number must be originated by the destination nodeThere is a trade off between the stability and the convergence speed of the routing table

System Architecture

Socket Layer

TCP

UDP

IP

IEEE 802.11 MAC Layer

ARP

Kernel Routing

Layer

Zebra Daemon

DSDV Daemon

Linux Kernel

IEEE 802.11

Network Interface

DSDV Router

RIB

Events of DSDV Protocol1.TimersPeriodical updates (30-second) Random offset timer (at most 30-second)Timeout (30-second)garbage-collection (120-second)2.Input processing Request Responseresponse to a specific queryregular updatestriggered updates triggered by a metric change3.Output Processing by input processing when a request is receivedby the periodical routing updateby triggered updates caused by changed route metric

Timers in DSDVPeriodical updates (T) send the full routing table to the neighbors. Random offset timer (

How does the DSDV Daemon workDSDV_Daemon(){Detect network interfaces and copy required information;Read configure file and initialize all variables and routing table;Create a UDP socket for DSDV routing messages;Send hello message to all neighbors;Install signal handlers for different kinds of timers;Loop for events (select())Different timers:Input processing:Output processing:Other system events:Loop end}

Geographical Routing

OverviewGeographical Routing using partial information for Wireless Ad Hoc Networks, R. Jain, A. Puri and R. Sengupta

A routing protocol for wireless ad hoc networks using information about geographical location of nodes.

ArchitectureMulti-threaded Location Advertisement ProtocolGeographic Routing ProtocolRoute Discovery ProtocolRouting Table Update Daemon

Assumes the presence of a GPS system at each node in the network

When a node receives data packet :

Check_final_destinationif (final_destination is a neighbor)forward the packetelsecheck the routing table, find the closest neighbor to this destination and then forward the packet to that neighborGeographical Routing Protocol

If a node can not send a packet to a destination because of a physical barrier it will use a DFS type of algorithm in order to find an alternate route to the destination.When the route discovery packet reaches the final destination, the destination node will send the packet back to the sender and this way the sender will discover the route to that specific destinationRoute Discovery Protocol

Packet FormatEth. HeaderGeog. HeaderData (if any)Route advertisement and route discovery packets dont need the data field (i.e. length field in the geographic header is equal to the length of the geographic header)Length field for Data packets is equal to the length of geographic header + length of dataWTP Hdr

Geographic HeaderSrc Loc + MACDst Loc + MACChecksum Location: UTM Location of the node MAC: MAC Addr of the node Checksum: checksum over the header Packet Len: length of the packet Seq: Sequence number Opts: options (TBD)p.lenseqopts

The Universal Transverse Mercator projection andgrid system was adopted by the U.S. Army in 1947for designating rectangular coordinates on largescale military maps. UTM is currently used by theUnited States and NATO armed forces.

Why UTM?Supported by all GPS receiversSimpler to use than latitude and longitude.UTM Coordinates

Demo Scenario MAC Filter Transport Layer WTP

DstGwCCBB

DstGwAABBCC

DstGwAABB

DstGwAABBCB

WOW Mobile IP

OverviewIP Mobility Support, C. Perkins, RFC 2002ProtocolsTunneling (HA FA)Registration (MA - FA - HA)Agent Advertisement (FA)

Mobile IPCorrespondent Host 10.0.1.4Home Agent 10.0.1.2Foreign Agent #1 10.0.2.2 & 11.0.1.2Foreign Agent #2 10.0.3.2 & 11.0.1.310.0.2.0 subnet10.0.3.0 subnet10.0.1.0 subnetRouter 10.0.1.110.0.2.110.0.3.1

RegistrationMobile needs to make the home agent aware of its present location i.e, the care of addressUsing UDPRegistration request (mobile -> home)Registration reply (home -> mobile) contains duration of validity (~100 seconds)What if UDP packet is dropped!!Request sent again after reasonable time

TunnelingEncapsulation is done for redirectionHome agent tunnels the packet to the care of addressDestination foreign agent de-tunnels the packet and transmits it to the mobilePackets from mobile to correspondent host go directly (with source IP as original (fixed) IP of the mobile node)

MA SoftwareListens the Agent Advertisement broadcasts sent by the FAsRegisters with FAs automatically depending on S/N over the link , signal qualities, BERThe bandwidth available on the linkThe encryption provided on the networkThe cost

Demo SetupCorrespondent Host 10.0.1.4Home Agent 10.0.1.2Foreign Agent #1 10.0.2.2 & 11.0.1.2Foreign Agent #2 10.0.3.2 & 11.0.1.310.0.2.0 subnet10.0.3.0 subnet10.0.1.0 subnetRouter 10.0.1.110.0.2.110.0.3.1CH: Netmeeting (video + audio)Mobile: OpenH323 Client

Intra-Domain Handoff DFA

Takes packet from HA or CH.

Decapsulates and checks its visitor list.

Sends the packet to the related branches according to Location FA table. FA

If it is an adjacent FA, buffer the packets.

Else send the packet to the related branches according to Location FA table.FAST HANDOFF with position based routing

FAST HANDOFF

FAST HANDOFFS with GPS for MOBILE IP

Motivation for Fast Handoff in Mobile IP Previous Work on Fast HandoffLocation Based Fast Mobile IP ProtocolProtocol DescriptionControl MessagesSecuritySimulation and ImplementationSystem Extensions Conclusion

Outline

Primary Aim of Mobile IPRobust communication between mobile users

Major Problem in Mobile IPAchieving QoS requirements of real-time applicationsSolution:High bandwidth through smaller cells

Motivation

Small Wireless CellsAdvantage:More number of users Diameter of cell decreases by Nnumber of cells in a certain area increases by Nnumber of available channels increases by NDisadvantage:Mobile host crosses cells more oftenMore number of handoffs

Motivation

HA

CH

Time Diagram of a Hand_off

Basic Mobile IP Handoff

Previous Work on Fast Handoff

Basic Mobile IP

Performs basic functionsTransparency and Handoff SupportNot optimized for handoff

Previous Work on Fast Handoff

Optimization in Mobile IP Hand-off

Through domainsDecreases overhead by localization of registrationStill suffers from delay and packet loss in intra-domain handoff Leaves inter-domain movement to the basic Mobile IP

Through multi-cast addressesAssigning multi-cast address to current access point and handoff targetsManual determination of handoff targetsRequires continuous messaging to learn about new multi-cast addressesMulti-cast address conflicts

Location Based Fast Mobile IP Protocol

Goals of the Protocol:

Support uninterrupted operation of real-time applicationsLower Handoff Delay, less Packet LossDecrease messaging burden of fast handoffAvoid manual configuration for fast handoffAvoid possible address conflicts


Structure of the internet

Intra-domain Uses geographical information . Finds adjacent FAs of the current attached FA. Send the datagram to the adjacent FAs besides current FA. Reduces handoff time and packet loss.

Inter-domain Gives HA functionality to a DFA Local Home Agent (LHA). Does not bother HA for movements within a geographical radius . Reduces handoff time and control messaging. Distribute HA database dynamically.


Intra-Domain Handoff Example

Soda Hall 3rd Floor

Intra-Domain Handoff

Internet

HA

DFA

FA

MH

FA

CH

FA

DFA

Takes packet from HA or CH.

Decapsulates packet and checks its visitor list.

Sends the packet to the related branchesaccording to Location FA table. FA

If it is current FA, send the packet to MN.

Else If it is an adjacent FA, buffer the packets.

Else send the packet to the related branches according to Location FA table.

Inter-Domain Handoff

Current inter-domain handoff compared to our system

Fast Inter-domain handoff necessary due toIncrease in the battery power of laptop computersTiling of the world into small wireless cells



Procedure of Inter-domain handoff in Basic Mobile IP:MH sends registration request to a FA in a new domainFA sends request to DFADFA sends request to HAHA sends registration reply to MHDisadvantage of Basic Mobile IP:Delay and packet loss due to wasteful trip of registration messages



Procedure of Fast Inter-domain handoff:MH sends registration request to a FA in a new domainFA sends request to DFADFA sends request to HA or local home agentHA or local home agent sends registration reply to MHAdvantage of Fast Inter-Domain Handoff:Decrease in delay and packet loss due to registration


How do we decide whether to register to a local home agent or HA ?

Register to old LHA instead of HA as long as DFA of MH is inside the circle

Angled1: Distance between LHA (DFA) and HAd2: Distance between LHA and Current DFAR : Movement range without changing LHA

Messaging: Registration Messages

TYPE

CODE

LIFETIME

HOME ADDRESS

TARGETED DOMAIN FOREIGN AGENT ADDRESS

IDENTIFICATION

LOCAL HOME AGENT IP ADDRESS

LOCAL HOME AGENT GEOGRAPHICAL LOCATION

OTHER EXTENSIONS

Registration Request Format

Registration Reply Format

Messaging: Location Advertisement Messages

Aim:Eliminate manual configurationDistribute the location of each FA to other FAs inside domain

Content:Location and CoA of the FA that it originates

Procedure:Every FA advertises its CoA and position to its neighborsEvery router sends the incoming LAM to its neighbors

Security

Uses security features of current Mobile IP(IPSec etc)

Requires security association between DFAs

New FA delivers buffered datagram to MH only after finishing secure registration

Simulation: Intra-Domain Handoff

Intra- Domain Handoff Scenario

Packet audio sourcePacket inter-arrival time: 20msAverage packet size: 200bytesConstant traffic to MH

Handoff Time = Discovery Time + Registration Time

Maximum Discovery Time = Beacon Period

Link: 2 Mbps, 4ms


Human ear can tolerate approximately 200 ms delay at maximum*We achieved 141ms max inter-arrival time*

Link: 2 Mbps, 4ms5 Mobile NodeBuffer Size 10


Simulation: Inter-Domain Handoff

Distance Number of nodes in between Delay

Inter- Domain Handoff Scenario

= arcsin 1/5

Simulation: Inter-Domain Handoff

Implementation: Intra-Domain Handoff

HA SoftwareTwo threadsRegistration protocolListens for UDP registration requestsUpdates Binding Table upon requestTunneling ProtocolListens to traffic in home networkSends packets for MH to its current CoA


DFA, FA SoftwareProcess 1: Agent Advertisement ProtocolSends out agent advertisements periodicallyProcess 2Thread1: Registration ProtocolUpdates Binding Table upon registrationSends all buffered packets if anyThread 2: Tunneling ProtocolSends packets to handoff targetsBuffers incoming packets if adjacent FA


MH SoftwareThread1: Listening threadListens for MAC layer packets to get the source address and sequence number of last packetThread 2: Registration ProtocolListens for agent advertisement messagesRegisters to new FA


Basic Mobile IPUnrecoverable throughput decrease during handoffLonger handoff period

Our Fast MIP schemeDecrease in throughput compensated by sending the packets missed during handoffShorter handoff period


Basic Mobile IPNumber of lost packets is constant for the same sending rateNo buffer used Number of lost packets increases as sending rate increases

Our Fast MIP schemePacket loss can be eliminated by choosing enough buffer size.Required buffer size increases as sending rate increases

System Extensions

Determining the location of indoor access points (FAs).

GPS support for only outdoor settingsLocation support for indoor environments viaUse of infrared signals (Active Badge Location System)Use of concurrent radio and ultrasonic signals (Cricket)

System Extensions

Roaming at the boundary of the domain

Introductory message to adjacent DFA with CoA and locationForwarding of packets to handoff targets by adjacent DFA

FA

FA

FA

FA

FA

FA

Domain A

Domain B

DFA

DFA

System Extensions

Avoiding Ping-pong effect

Registration to new access point like a registration updatePackets are already in new FA

FA

FA

MH

DataRegistration

time

Conclusion

Goal QoS for Wireless Real Time ApplicationDistributing Home Agent FunctionalityIntra-domain Handoff Sends packets to handoff targetsInter-domain Handoff Geographical Boundary and Local Home AgentMessaging SecuritySimulationRegistration time, Packet inter-arrival timeImplementationInstantaneous throughput, Buffer sizeSystem extensions

Hierarchical structure can be formed with a messaging which works with very large period or a change in the structure of the network

MEWLANAMobile Enriched Wireless Local Area Network Architecture

MEWLANA-Mobile IP Enriched Wireless Local Area Network Architecture

Introduction

Mobile IP & Ad-Hoc Networks OverviewMotivationNetwork Architecture

Protocol

Previous Work -MIPMANET -on demand routingMEWLANA-TD - table driven routingMEWLANA-RD - root driven routing (mesh networks)

Performance AnalysisConclusion

Mobile IP & Ad-Hoc Networks

Mobile IPRetain a fixed IP identity while moving.Mobile Node (MN)Home Agent (HA)Foreign Agent (FA)Correspondent Host (CH)Agent AdvertisementRegistrationTunneling

Ad-Hoc Network No network infrastructure.Special routing protocol

Motivation

Mobile IP in Ad hoc NetworkHigh cost for building a large number of bases.Total throughput limited by the number of cells in the area.High power consumption of mobile stations having the same transmission range as bases. Ad hoc networks are limited to be small scale.

The number of bases or the transmission ranges of both mobile stations can be reduced.Connections are still allowed without base stations.Multiple packets can be simultaneously transmitted within a cell. Paths are less vulnerable than the ones in ad hoc networks because the bases can help reduce the wireless hop count.

Motivation

Does this new architecture impose new traffic characteristics?Inside traffic, Outside Traffic

Can we classify the environment based on the traffic characteristics?Small or large size ad hoc networkIntensity of inside and outside traffic

Does using one kind of ad hoc routing give optimum result in all environments?

Motivation

Intensity of outside traffic = constant

A conference

Big Size NetworkHigh Inside Traffic

A subway

Big Size NetworkNegligible Inside Traffic

A rescue mission

Small Size NetworkHigh Inside Traffic

Example

Network Architecture

Ad Hoc Routing Protocols

Table Driven Routing DSDV,

On Demand RoutingAODV,

Route Driven Routing TBBR (Tree Based Bidirectional Routing)

Tree Based Bidirectional Routing

MESH NETWORK

Root : Foreign AgentBranches: Mobile NodesRoot periodically initiates protocolBidirectional RoutesRoutes FA to MN and MN to FA

Protocol-Main Components

Discovering Base StationUnicast or Broadcast

Registration MechanismInform the HA of the current location of the mobile.

Tunneling Mechanism from HA to FA

Delivery from FA to mobile FA keeps a table Gateway mobile MAC address and Source IP address pair.

Gateway Mobiles

Beacon: Agent Advertisement Message (modified ICMP)

Domain specific info: DNS, CoA, hop count, source address.

MN duplicates the beacon : hop count ++

Hop count is to limit the serviced nodes and a decision mechanism

MN`s new access point = CoA

Mobile establish the route to the FA

Protocol-Agent Discovery

Protocol-Registration & Tunneling

Normal Mobile IP Registration

Registration Request: MN4->MN3->MN2->MN1->FA->HA Registration Reply: HA->FA->MN1->MN2->MN3->MN4 Periodic registration update.

Ethernet Header FA addr. HA addr. MN addr. CH addr. Packet

MN addr. CH addr. Packet

Ethernet Header MN addr. CH addr. Packet

Gateway Mobile Node MAC Address

Decapsulating at FA

Sending to MN at FA

Encapsulating at HA

Tunneling

Protocol-Hop Count

Lifetime of agent advertisement = # of hop countChange access point by considering hop count.

A

B

C

D

E

F

FA

FA2

MN1

MN2

Ad hoc Domain

Protocol-OVERHEAD

MIPO: Mobile IP OverheadBeacon Flooding

AHRO: Ad Hoc Routing Overhead Routing Table Formation

NHIT: Number of Hops for Inside Traffic Wireless bandwidth usage

Previous Work-MIPMANET

Designed with on demand routing

Agent AdvertisementBeacon Flooding

Ad Hoc RoutingAODVCreate route before sending

High MIPOAHRO depends on traffic and sizeNHIT depends on traffic and size

MEWLANA-TD

Designed with table driven routing

Agent Advertisement: Dynamic BeaconingInitiate advertisement when the routing table changes

Ad Hoc RoutingDSDV- route table exchange

MEWLANA-TD

Dynamic BeaconingThere exists a route for each node

Low MIPOAHRO depends on sizeNHIT depends on size and traffic

Sheet1

DestinationNext Hop

MN1MN2MN2

MN3MN2

MN4MN2

FAFA

*FA

MN2MN1MN1

MN3MN3

MN4MN3

FAMN1

*MN1

MN3MN4MN4

MN2MN2

MN1MN2

FAMN2

*MN2

MN4MN3MN3

MN2MN3

MN1MN3

FAMN3

*MN3

Table 1 : Routing Tables

MEWLANA-RD

Depth Level Number (DLN): Hop Count -> eliminate loopRoutes (1) From mobile to FA : Beacon Routes (2) From FA to mobiles: Multi Hop Registration Request

MEWLANA-RD

Multi Hop Registration Request Mechanism

MEWLANA-RD

Beacon floodingCreate treePerformance degradation in inside trafficIf in different tree, connect with Mobile IP

High MIPONo AHROHigher NHIT

Empirical Classification

Low

High

Small

Large

Intensity level of Inside traffic

Ad Hoc network size

MIPMANET

MEWLANA-RD

MEWLANA-TD

III

II

I

IV

Simulation Parameters

NS-2

CBR Source : 1-1010 packets per second512bytesBeacon Period: 1 sec.Nodes:{4,8,32,64,128}PF: Performance Factor B=C=D=1A is a scaling factor

Simulation

Performance Factor

Conclusion

Classification of the environmentSize and traffic intensity

MEWLANA-TD : Small size and High inside trafficDynamic Beaconing

MEWLANA-RD: Large size and Low inside trafficEliminate Ad hoc Routing Protocol Overhead

MIPMANET : Large size and High inside trafficDemand routing protocol when there is a need.

Reference

Royer, C. Toh, A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks IEEE Personal Communications, Vol. 6, No.2, pp.46-55, April 1999.

Broch J., Maltx D. ,Johnson D.,Hu Y.,Jetcheva J., A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols, The fourth annual ACM/IEEE International conference on Mobile computing and networking, October 25-30, 1998, Dallas, TX USA

Ulf Jonsson, Fredrik Alriksson, Tony Larsson, Per Johansson, Gerald Q. Maquire Jr. MIPMANET-Mobile IP for Mobile Ad Hoc Networks, MOBIHOC 2000.

Hui Lei and Charles E. Perkins, Ad hoc networking with Mobile IP in Proceedings of 2nd European Personal Mobile Communication Conference, Sept. 1997.

SENSOR NETWORKS

Scheduling and Positioning Problems for Sensor Networks

Outline

Introduction PositioningScheduling Wireless NetworksWireless Tree Networks

Parking Garage Problem

A sensor node at each parking spotA sensor node determines whether a car is present and informs the BSBS has global knowledge of state of the garageGuide cars to empty spotsCharging for time used

Energy consumption in sensor nodes

Some comparisons:Bluetooth:~40 mW power consumption2 mW tx output-80 dbm receiver sensitivityRange ~ 10m802.11:~ 1 W power consumption30 mW tx output-82 dbm receiver sensitivityRange ~ 25-100m1 AAA battery has about:1000 mW Hour of energy

Asymmetric Communication

BS have lots of energy and processing powerSensor nodes have little energy and processing powerUse BS to coordinate sensor nodesSensor nodes collect and send data to BSBS communicates directly with sensors. Sensors send data over multiple hops

Received Power and Positioning

Fact: Received power is corelated with locations of sender and receiverCellular Models:Average_Rx_Power (in dB) = -10 a log(R) + N(0,b)Indoor Models:Average_Rx_Power = M(t,r) + N(0,b)

Bayesian Inference

K transmitters at fixed known locationsProblem: determine location of receiverRandom Variables:R1, , Rk received powers from the k transmittersX location of the receiverGiven: P(Ri = a | X = x)

Bayesian Inference (cont.)

Determine:P(X = x | R1=a1, R2=a2, , Rk=ak) = P(R=a|X=x)P(X=x)/R(R=a)Assuming independence:P(R=a|X=x) = P(R1=a1|X=x)P(Rk=ak|X=x)Maximum likelihood:argmax_{x} P(R=a|X=x)

Positioning when Tx have unknown positions

Random Variables:Y1, , Yk unknown locations of nodes R[i,j] - received power at node i from node jWe know: P( R[i,j] | Yi, Yj)Compute: P( Yi | R )

Scheduling in Wireless Networks

Paths of flows fixed through the wireless networkFluid flow/discrete packetsWireless constraintsConstraint graph: C = (E,F) where F \subset E x EProblem: empty the network

Scheduling in Wireless Networks (cont.)

Each node i has x(i) amount of trafficEach link l has t(l) amount of trafficGeneralized graph coloring of links

Greedy Policy

Greedy Policy: choose the maximum number of nodes to be fired.Is this a good policy ?

A Schedule

Schedule periodically announced by the BSOnly receivers and transmitters need to be on during a time slot

TimeSenderReceiver

01,24,5

12,35,6

23,48,9

Other Issues

Determining a schedule based on demand pattern or data collection patternSynchronizing the nodes

Wireless Tree Networks

Traffic light:BS calculates the number of cars waiting from the number of cars passed through each sensorRequirements:Generate packets in each node almost at the same time for a better estimate of the # of cars between each sensorMinimize the period each sensor sends the data to BS without overloading networkGuarantee the arrival of packets within a specific deadline


Parking garage:BS determines free spaces from the packets received from sensor nodesRequirements:Guarantee the arrival of packets within a specific deadlineMinimize the period each sensor sends the data to BS without overloading network


How can we achieve these requirements?Assumptions:BS has full knowledge of the networkEvery node knows its parent in the treeBS announces the scheduleNodes synchronized by BSDefn: Frame is the duration of time of length equal to the packet generation period at each node


How can we achieve these requirements?Procedure:Each node generate one packet at the beginning of the frameEach nodes packet is guaranteed to reach BS until the end of the frameAdvantages:Each packet is generated at the same time(traffic light)Maximum delay to reach BS is bounded by frame lengthPacket generation rate is low enough not to overload the networkExactly one packet from each sensor node reaches BS(fair, otherwise some scheme like Alec Woos scheme required

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