Reversing the Collision Avoidance Handshake in Wireless Networks

Reversing the Collision Avoidance Handshakein Wireless Networks

J.J. Garcia-Luna-Aceves and Makis Tzamaloukas (jj,jamal@cse.ucsc.edu)

Computer and Communications Research Group (CCRG)http://www.cse.ucsc.edu/research/ccrg

Computer Engineering DepartmentJack Baskin School of Engineering

University of CaliforniaSanta Cruz, CA 95064

MobiCom '99, 15-20 August

JJ. Garcia-Luna-Aceves and A. Tzamaloukas

Presentation Outline

Sender-Initiated Collision Avoidance Protocols Motivation Polling Issues Correct Collision Avoidance RIMA protocols Throughput and Delay Analysis Conclusions

Sender-Initiated Protocols

SRMA (Kleinrock and Tobagi, August ‘76) MACA (Karn, April ‘90) MACAW (Bharghavan, Demers, Shenker

and Zhang, August ‘94) FAMA (Garcia-Luna-Aceves and Fullmer,

September ‘97) IEEE 802.11 (July ‘97)

Motivation

The recipient of data packet is the point of interest Recast the collision avoidance dialogues so that the receiver,

sender or both can have control of the dialogue Provide equal or better throughput than any sender-initiated

IEEE 802.11-like MAC protocol Be applicable to multi-channel frequency-hopping or direct-

sequence spread-spectrum radios To date no receiver-initiated MAC protocol ensures correct

collision avoidance The receivers poll the senders

Ensuring Correct Collision Avoidance

First receiver-initiated MAC protocol was MACA-BI (Talucci and Gerla):– a node sends a DATA packet if it has

previously received an RTR– a polled node can send a DATA packet either to

the polling node or to any other neighbor– does not guarantee correct floor acquisition

At time t0, nodes a and d send RTRs to b and e; at time t1 both b and e send DATA to c resulting in a collision

t0 RTR to b RTR to e

DATA to ct1 DATA to c

At time t0, node a sends an RTR to b; at time t1, b sends DATA to a; at time t2 < t1 + , c sends an RTR to d; at time t3, d sends DATA to c; if data packets last longer than + 3 the DATA from b and d collide at c

a b c d

t0 RTR

DATAt1

With RIMA-SP correct floor acquisition is guaranteed:– the polled node transmits a DATA packet only to the polling node– a collision avoidance period of seconds is required at a polled node prior to answering an RTR; we have shown that =

– an additional control signal is introduced; we call this signal No-Transmission-Request (NTR)

RIMA-SP illustrated

RTR ZX

X Zdata

RTRRTR

BACKOFF

RTR ZX

NTR ZX

Successful handshake

Colliding RTRs

Hidden node interference

RIMA-SP timing diagrams

RTRWaiting period

RTR NTR BACKOFFX

Z interference

collision

channel BACKOFF

Node X sends an RTR and after seconds receives a DATA packet

Nodes X and Z send RTRs within seconds and therefore a collision occurs

Due to interference from node Z, nodeX sends an NTR to stop the handshake

Noise detected at Z

Polling Issues

When to poll: whether or not the polling rate is independent of the data rate at polling nodes– independent polling– data driven polling

To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule must be provided to the poll recipients

How: whether the polling packet asks for permission to transmit as well

RIMA Protocols

Polling done with RTR (Request-To-Receive) packet Three Receiver Initiated Medium Access (RIMA) protocols

defined based on the type of polling:– RIMA-SP: A simple poll receiver initiated protocol

(only the receiver sends data in a successful busy period)– RIMA-DP: A dual poll receiver initiated protocol (2

data packets are sent in the same successful busy period)– RIMA-BP: A broadcast poll receiver initiated protocol

(the RTR is sent to everybody)

RIMA-DP illustrated

X ZCTS

dataZX

RTR ZX

X Zdata

data ZX

BACKOFF

NTR ZX

NTRdata

Success 1

Success 2

Failure 1 Failure 2

RIMA-DP timing diagrams

RTR NTR

Noise detected at Z

BACKOFFX

Z interference

RTRWaiting period

collision

channel BACKOFF

Node X sends an RTR and after seconds receives a DATA packet and then sends its DATA

Node X sends an RTR and node Z replies with a CTS; node X sends its DATA

Due to interference from node Z, node X sends an NTR to stop the handshake

RIMA-BP illustrated

BACKOFF

X ZRTS data

RTR ZX

X ZRTS

RTSRTS

Success 1

Failure 1

Failure 2

RIMA-BP timing diagrams

collision

channel BACKOFF

RTRWaiting period

DATARTS

collision NTR

Node X sends an RTR; node Z responds with a RTS and after seconds sends its DATA

Node X sends an RTR; nodes Z and Y send an RTS within seconds; node X sends an NTR to stop the handshake

Throughput Analysis Model

fully-connected network of N nodes single, unslotted channel, error-free the size for an RTR, RTS and CTS is seconds; the size for a

data packet is seconds the turn-around time is considered to be part of the duration of

control and data packet the propagation delay of the channel is seconds a polled node receiving an RTR always has a data packet to

send the probability that the packet is addressed to the polling node

is 1/N

Throughput Analysis

500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; on the left a 10 node network; on the right a 50 node network

1a = 0.00025; b = 0.04; c = 0.005

Offered Load: G

MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___

RIMA-BP xxx

1a = 0.00025; b = 0.04; c = 0.005

Offered Load: G

MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___

RIMA-BP xxx

Delay Analysis

500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 110

a = 0.0001; b = 0.02; c = 0.002

S (throughput)

FAMA RIMA-DP

Heavy Traffic Approximation

MACA-BI analysis assumes that there is always a DATA packet after a successful poll

To present a fair comparison between MACA-BI and RIMA protocols we analyze a heavy load approximation where there is always a DATA packet to be sent after receiving an RTR

Throughput Analysis

500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; network of 50 nodes; heavy load approximation throughput: any polled node always has data to send to any polling node

1a = 0.00025; b = 0.04; c = 0.005

Offered Load: G

t)MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___

RIMA-BP xxx

Conclusions

RIMA protocols provide correct collision avoidance in the presence of hidden terminals

The throughput achieved with RIMA-DP is higher than any other sender initiated MAC protocol for fully connected networks

RIMA-DP achieves higher throughput than all other collision avoidance protocols in fully-connected networks under heavy load approximation

Relative differences in performance remain the same in networks with hidden terminals

Simulation Results

BaseN1

(a) (b)

Simulation Results

Network RIMA FAMA MACAW

(a) .83 .76 .63

(b) .58 .58 .49

(c) (B1) .76 .74 .45

(d) (B2) .76 .74 .39

Reversing the Collision Avoidance Handshake in Wireless Networks

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