1. Performance Enhancement of TFRC in Wireless Ad Hoc Networks Travis Grant – grant_travis@emc.comgrant_travis@emc.com Mingzhe Li, Choong-Soo Lee, Emmanuel Agu, Mark Claypool, and Robert Kinicki WPI

2. Worcester Polytechnic Institute 2 Outline Introduction & Background RE-TFRC Evaluation

3. Worcester Polytechnic Institute 3 TFRC - Background TCP Friendly Rate Control (RFC 3488) CC Mechanism that reduces variation of throughput Ideally suited for Applications sensitive to “jitter” as opposed to overall transfer times Receiver Sender (1) Rcvr measures loss event rate ( p ) & passes info back to sender (2) Sender uses info to calculate RTT ( r ) (4) Sender adjusts transmit rate to match calculated rate X (3) Sender passes loss event rate & RTT into TFRC Equation Calculated Dynamic Constant X=T = Transmit Rate p = loss event rate R=r = RTT t rto =TCP RTO s =packet size b = #of packets acked by single TCP ack FLOYD00 RFC 3488

4. Worcester Polytechnic Institute 4 Wireless Challenges 802.11 Solution to the Hidden Terminal Problem –Use a four-way handshake: RTS-CTS-DATA-ACK where the RTS and CTS packets are significantly smaller than the average data packet. –The maximum number of RTS retransmissions is set to 7 MAC Layer Congestion can increase in Chained Ad- Hoc Topologies

5. Worcester Polytechnic Institute 5 MAC Layer Saturation First Simulation is a 7-hop NS-2 with a constrained sending rate Wireless traffic load is increased above MAC Layer saturation point lower layer contention, RTS/CTS Jamming, can be hidden –Could still see a successful ack at the transport layer after 6 MAC Layer retransmission occurred TFRC Calculates a send rate that is too high –R=RTT & P=Loss Event Rate are ineffective Link Capacity = 2Mbps max throughput = 0.146

6. Worcester Polytechnic Institute 6 Outline Introduction & Background RE-TFRC Evaluation

7. Worcester Polytechnic Institute 7 RE-TFRC Rate Estimation TFRC Goals 1.minimize round trip time 2.maintain, or slightly improve, throughput 3.solve the “mis-interaction” between TFRC and 802.11 MAC Layer (w/o changing the MAC layer) Optimum sending rate based on: –The number of hops in the flow path –The current loss event rate –Respects TFRC ceiling Effectively avoids RTS/CTS Jamming compared to TFRC

8. Worcester Polytechnic Institute 8 Loss event rate for various RTT Floyd97 TCP Westwood window = B x r min Simple TFRC r opt =

9. Worcester Polytechnic Institute 9 RE-TFRC Rate Estimation X: TCP Friendly rate p: TFRC loss event rate R: TFRC estimated receiving rate p’: Adjusted TFRC loss event rate R’: Estimated optimum sending rate TFRC Simple Inverse TFRC Use R to estimate p’ Use p’ to estimate R’ Receiver Sender (1) p & R (2) r (RTT) (4) R’ is used to adjust transmit rate (3) Sender passes loss event rate & RTT into TFRC Equation

10. Worcester Polytechnic Institute 10 Optimum RTT = r opt Represents the min. RTT during MAC layer saturation Helps account for queuing at individual nodes = avg. MAC layer back off time = time required to successfully transmit a packet (r(N)) assumes saturation of the MAC layer and can therefore be used for r opt for an N hop ad hoc wireless network

11. Worcester Polytechnic Institute 11 RE-TFRC Algorithm

12. Worcester Polytechnic Institute 12 Outline Introduction & Background RE-TFRC Evaluation

13. Worcester Polytechnic Institute 13 Evaluations Core Experiments –detailed analysis of a 7 hop NS-2 simulation –# of hops is varied from 4 to 15 (& multiple flows) –typical Bit Error Rate network environment

14. Worcester Polytechnic Institute 14 7 hop simulation RE-TFRC has lower probability of retransmissions

15. Worcester Polytechnic Institute 15 Varied hop count simulation MAC layer drop ratio is reduced 13% to 66%

16. Worcester Polytechnic Institute 16 Varied hop count simulation RTT for RT TFRC is 5% to 40% lower

17. Worcester Polytechnic Institute 17 Varied hop count simulation RE-TFRC loss event rate is 8% to 55% less

18. Worcester Polytechnic Institute 18 BER Evaluation 7-hop wireless network with single flow simulation

19. Worcester Polytechnic Institute 19 References & Acknowledgments RFC 3488 Floyd97 Memo - “TCP-Friendly Unicast Rate-Based Flow Control” Floyd00 “Equation-Based Congestion Control for Unicast Applications” Kinicki04 Presentation on “ Performance Enhancement of TFRC in Wireless Ad Hoc Networks”

20. Worcester Polytechnic Institute 20 Backup Slides

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