TCP Friendliness CMPT771 Spring 2008 Michael Jia.
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Transcript of TCP Friendliness CMPT771 Spring 2008 Michael Jia.
TCP Fairness
R
R
equal bandwidth share
Connection 1 throughputConnect
ion 2
th
roughput
Fair: 1. Equal share
2. Full utilizationif K TCP sessions share same bottleneck link of bandwidth R, each should have average rate of R/K
Why UDP?
UDP Preferred Applications• Video Streaming• VoIP
UDP Advantages• Simplicity • Lower overhead (light weight)• No re-transmission required
Problem with UDP: Unresponsive Flows
• No congestion control• No response to packet drops• TCP competing with unresponsive UDP
– TCP flows reduce sending rates in response to congestion
– Uncooperative UDP flows capture the available bandwidth
– Unfair to TCP, or even starve TCP
Objective: TCP-friendly
TCP TCP
Internetnon-TCP
non-TCP
“ long-term throughput does not exceed the throughput of a conformant TCP connection under the same conditions”
Classification
• Window-Based vs. Rate-Based– window-based:
• Window size controls rate• Sender or receiver(s)• Similar to TCP
– rate-based:• TCP throughput models• More smoother rate• Good for media streams
Classification
• Unicast vs. Multicast– Multicast: more difficult– RTT is required for Rate-based schemes– Window-based approach is more suitable
• Single-rate vs. Multi-rate– Unicast = Single-rate– Multicast: multi-rate protocols are preferred
• More flexible allocation of bandwidth• Layered multicast• Group management
TCP Throughput Equation 1R -- Bandwidth of TCP connection (Long term throughput)T -- Round-trip delay T (RTT)L --Packet size Lp -- Loss event rate p
T. Ott, J.H.B. Kemperman, M. Mathis, 1996
The Stationary Behavior of Ideal TCP Congestion Avoidance
TCP Throughput Equation 2
22 3(3 ) (1 32 )
3 8RTO
LR
q qT T q q
=+ +
Padhye, J., Firoiu, V., Towsley, D., and Kurose, J., Modeling TCP Throughput: a Simple Model and its Empirical Validation, UMASS CMPSCI Tech Report TR98-008,
Feb. 1998.
R -- Bandwidth of TCP connection
T -- Round-trip delay T (RTT)
L --Packet size L
q -- Loss event rate q
TRTO -- Retransmission timeout (~ 4T)
TCP Throughput Equation
M. Mathis, J. Semke, J. Mahdavi, and T. Ott. The macroscopic behavior of the TCP congestion avoidance algorithm.
Computer Communication Review, 27(3), July 1997
• Verify through simulation & live Internet measurements
• Assumption– Steady State (Ignore slow start phase & No timeouts)
– Constant packet size
Achievements - TFRC
• TCP-Friendly Rate Control Protocol (2000)• Unicast, rate-based• Based on TCP equation 2
• Using more sophisticated methods to gather parameters– Average-Loss-Interval loss rate estimation
• Stable sending rate• Sufficient responsiveness
Achievements - TEAR
• TCP Emulation At Receivers (2000)• Multicast, single-rate• Rate-based + Window-based• Receiver maintains a congestion window• Receiver calculates average rate
– then send back to the sender– avoid saw-tooth-like behavior
• Scalable in multicast case– use the minimum rate
Achievements – Rainbow
• Rainbow (2000)• Multicast, multi-rate,
window-based• Digital-Fountain• Receivers individually
request each data packet• Routers process requests• Receiver controls
congestion• Limitation – router
supporting
Challenges
• Lack of standard methods for comparison
• Fairness definitions for multicast
• Improvement of the models for TCP traffics
• How to treat short-lived flows
• Much more…
References• Robert Denda Joerg Widmer and Martin Mauve, 2001, A
survey on tcp-friendly congestion control
• T. Ott, J.H.B. Kemperman, M. Mathis, 1996, The Stationary Behavior of Ideal TCP Congestion Avoidance
• Padhye, J., Firoiu, V., Towsley, D., and Kurose, J., 1998, Modeling TCP Throughput: a Simple Model and its Empirical Validation
• M. Mathis, J. Semke, J. Mahdavi, and T. Ott., 1997, The macroscopic behavior of the TCP congestion avoidance algorithm
• Jitendra Padhye Sally Floyd, Mark Handley and Joerg Widmer, 2000, Equation-based congestion control for unicast applications
• Volkan Ozdemir Injong Rhee and Yung Yi., 2000, Tear: Tcp emulation at receivers – flow control for multimedia streaming