Performance Enhancement of TFRC in Wireless Ad Hoc Networks

1
Performance Enhancement of TFRC in Wireless Ad
Hoc Networks
Mingzhe Li, Choong-Soo Lee, Emmanuel Agu, Mark
Claypool, and Robert KinickiWPI

• Travis Grant grant_travis_at_emc.com

2
Outline

• Introduction Background
• RE-TFRC
• Evaluation

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

(1) Rcvr measures loss event rate (p) passes
info back to sender
(2) Sender uses info to calculate RTT (r)
(3) Sender passes loss event rate RTT into TFRC
Equation
Receiver
Sender
(4) Sender adjusts transmit rate to match
calculated rate X
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
MAC Layer Saturation
Link Capacity 2Mbps
max throughput 0.146

• 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
• RRTT PLoss Event Rate are ineffective

6
Outline

• Introduction Background
• RE-TFRC
• Evaluation

7
RE-TFRC

• Rate Estimation TFRC
• Goals
• minimize round trip time
• maintain, or slightly improve, throughput
• 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
Loss event rate for various RTT
ropt
Floyd97
TCP Westwood
window B x rmin
Simple TFRC
9
RE-TFRC Rate Estimation
(2) r (RTT)
(1) p R
(3) Sender passes loss event rate RTT into TFRC
Equation
Receiver
Sender
(4) R is used to adjust transmit rate
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
10
Optimum RTT ropt

• 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 ropt for an N hop ad
hoc wireless network
11
RE-TFRC Algorithm
12
Outline

• Introduction Background
• RE-TFRC
• Evaluation

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
7 hop simulationRE-TFRC has lower probability of
retransmissions
15
Varied hop count simulationMAC layer drop ratio
is reduced 13 to 66
16
Varied hop count simulationRTT for RT TFRC is 5
to 40 lower
17
Varied hop count simulationRE-TFRC loss event
rate is 8 to 55 less
18
BER Evaluation

• 7-hop wireless network with single flow
  simulation

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
Backup Slides
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)