A Bidirectional Multi-channel MAC A Bidirectional Multi-channel MAC Protocol for Improving TCP Protocol for Improving TCP

Performance on Multihop Wireless Ad Performance on Multihop Wireless Ad Hoc NetworksHoc Networks

Tianbo Kuang and Carey WilliamsonTianbo Kuang and Carey WilliamsonDepartment of Computer Science University of CalgaryDepartment of Computer Science University of Calgary

ACM MSWiM 2004ACM MSWiM 2004(Modeling, Analysis and Simulation of Wireless and Mobil(Modeling, Analysis and Simulation of Wireless and Mobil

e Systems)e Systems)

OutlineOutline IntroductionIntroduction Bi-MCMACBi-MCMAC

ExtensionsExtensions SimulationsSimulations

ThroughputThroughput FairnessFairness Transfer delayTransfer delay

ConclusionsConclusions

IntroductionIntroduction

A well-known problem of multihop ad hoc A well-known problem of multihop ad hoc wireless networks is the wireless networks is the hidden node problemhidden node problem

IEEE 802.11 MAC Protocol attempts to solve IEEE 802.11 MAC Protocol attempts to solve the problem by using the problem by using RTS/CTS handshakeRTS/CTS handshake But But RTS collisionRTS collision andand Exposed node problemExposed node problem are are

not completely solved.not completely solved.

Introduction Introduction (cont.)(cont.)

For a transport-layer protocol working above For a transport-layer protocol working above RTS/CTS based protocol, the problems RTS/CTS based protocol, the problems described above will described above will affect the network affect the network performanceperformance

Problem descriptionProblem description

Hidden nodeHidden node When data packets travel in When data packets travel in the samethe same direction direction

1 2 3 4 5

sender receiver

RTS

interference

transmission

hidden

collision

Problem description Problem description (cont.)(cont.)

Exposed nodeExposed node When data packets travel in When data packets travel in oppositeopposite direction direction

1 2 3 4 5

sender receiver

RTS

interferenceno transmission

transmission

Problem description Problem description (cont.)(cont.)

Capture effectCapture effect UnfairnessUnfairness can occur between different TCP flows can occur between different TCP flows

1 2 3 4 5

sender receiver

RTS

interference

transmission

senderreceiver

hidden

collision

Related worksRelated works C. Cordeiro, S. Das, and D. Agrawal. COPAS: Dynamic conte

ntion-balancing to enhance the performance of TCP over multi-hop wireless networks. In Proceedings of ICCCN’02, pages 382–387. Miami, FL, USA, October 2002.

GoalGoal

Design a multi-channel MAC protocol to Design a multi-channel MAC protocol to reduce TCP DATA-DATA collisionreduce TCP DATA-DATA collision

Use bidirectional RTS/CTS channel Use bidirectional RTS/CTS channel reservations to reduce TCP DATA-ACK reservations to reduce TCP DATA-ACK contentioncontention

Bi-MCMACBi-MCMAC

Static multihop wireless ad hoc networksStatic multihop wireless ad hoc networks One control channel, One control channel, K-1K-1 data channels data channels Single transceiverSingle transceiver Extends the RTS/CTS handshake to do the Extends the RTS/CTS handshake to do the

bidirectional channel reservationbidirectional channel reservation CRNCRN ( (CChannel hannel RReservation eservation NNotification) control otification) control

frameframe

Bi-MCMAC Bi-MCMAC (cont.)(cont.)

Channel stateChannel state is included in RTS/CTS frames is included in RTS/CTS frames CRN frame is sent after the sender receives CRN frame is sent after the sender receives

CTS, containing the CTS, containing the channelchannel and and reservationreservation durationduration information information

Subsequent data frame sent by receiver is Subsequent data frame sent by receiver is indicated as indicated as MAC-layer ACKMAC-layer ACK

Bi-MCMACBi-MCMAC (cont.)(cont.)Channel: 1,5,7,11

Channel: 2,6,7,11Choose 7

Announce channel 7 and

CRN NAV Indicated as MAC-layer ACK

ExtensionExtension

Head-of-Line (HOL) blockingHead-of-Line (HOL) blocking If the first packet in the buffer is If the first packet in the buffer is notnot destined to destined to

the senderthe sender Per-neighbor queuePer-neighbor queue

Multi-channel Hidden Terminal ProblemMulti-channel Hidden Terminal Problem Receiver always selects the channel used for the Receiver always selects the channel used for the

last successfullast successful transmission transmission

Further workFurther work

Heterogeneous channel ratesHeterogeneous channel rates If all the data channel are 54Mbps and the control If all the data channel are 54Mbps and the control

channel is 1Mbps, then the control channel may channel is 1Mbps, then the control channel may become become congestedcongested

SimulationsSimulations

ThroughputThroughput FairnessFairness

Strict senseStrict sense General senseGeneral sense

Transfer delayTransfer delay

Chain topologyChain topology Grid topologyGrid topology Random topologyRandom topology

Sparse (500*500)Sparse (500*500) Dense (250*250)Dense (250*250)

100 nodes100 nodes 300 seconds, 50 repetition300 seconds, 50 repetition

Environmental parametersEnvironmental parameters

Data packet size: Ld

Control packet size: Lc

Maximum number of channels should not exceed Ld/3Lc

Ex: 1000/3*64

Throughput in chain topologyThroughput in chain topology

Collisions in chain topologyCollisions in chain topology

Throughput in grid topologyThroughput in grid topology

Throughput in sparse random Throughput in sparse random topologytopology

Throughput in dense random Throughput in dense random topologytopology

FairnessFairness

Strict senseStrict sense Similar path and competitionSimilar path and competition

General senseGeneral sense Share the same channels Share the same channels

regardless of their local regardless of their local contentioncontention

Jain’s Fairness Index (FI)

Strict sense fairnessStrict sense fairness

General sense fairness in grid General sense fairness in grid topologytopology

General sense fairness in sparse General sense fairness in sparse random topologyrandom topology

General sense fairness in dense General sense fairness in dense random topologyrandom topology

Web transfer timeWeb transfer time

Web transfer time Web transfer time (cont.)(cont.)

ConclusionsConclusions

The Bi-MCMAC protocol is explicitly The Bi-MCMAC protocol is explicitly designed to designed to improve TCP performanceimprove TCP performance over a over a static multihop wireless ad hoc networkstatic multihop wireless ad hoc network

Bi-MCMAC extends IEEE 802.11 RTS/CTS Bi-MCMAC extends IEEE 802.11 RTS/CTS handshake to do bidirectional channel handshake to do bidirectional channel reservations reservations

Conclusions Conclusions (cont.)(cont.)

Subsequent data frame resolves the TCP Subsequent data frame resolves the TCP DATA-ACK problemDATA-ACK problem

Simulations show thatSimulations show that Throughput improvedThroughput improved Lower transfer delayLower transfer delay Good fairnessGood fairness

Its Its unfairness unfairness in thein the single-cell casesingle-cell case is a minor is a minor disadvantagedisadvantage

Thank you !Thank you !