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TCP Friendliness. CMPT771 Spring 2008 Michael Jia. Outline. Background Classification Achievements Challenges. TCP F air ness. Fair: 1. Equal share 2. Full utilization if K TCP sessions share same bottleneck link of bandwidth R, each should have average rate of R/K.

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slide1

TCP Friendliness

CMPT771

Spring 2008

Michael Jia

slide2

Outline

  • Background
  • Classification
  • Achievements
  • Challenges
tcp f air ness
TCP Fairness

Fair:1. Equal share

2. Full utilization

if K TCP sessions share same bottleneck link of bandwidth R, each should have average rate of R/K

equal bandwidth share

R

Connection 2 throughput

Connection 1 throughput

R

why udp
Why UDP?

UDP Preferred Applications

  • Video Streaming
  • VoIP

UDP Advantages

  • Simplicity
  • Lower overhead (light weight)
  • No re-transmission required
problem with udp unresponsive flows
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
Objective: TCP-friendly

“long-term throughput does not exceed the throughput

of a conformant TCP connection under the same conditions”

non-TCP

non-TCP

Internet

TCP

TCP

slide7

Outline

  • Background
  • Classification
  • Achievements
  • Challenges
classification
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
classification1
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
slide10

Outline

  • Background
  • Classification
  • Achievements
  • Challenges
tcp throughput equation 1
TCP Throughput Equation 1

R -- Bandwidth of TCP connection (Long term throughput)

T -- Round-trip delay T (RTT)

L --Packet size L

p -- 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
TCP Throughput Equation 2

R -- Bandwidth of TCP connection

T -- Round-trip delay T (RTT)

L --Packet size L

q -- Loss event rate q

TRTO -- Retransmission timeout (~ 4T)

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.

tcp throughput equation
TCP Throughput Equation
  • Verify through simulation & live Internet measurements
  • Assumption
    • Steady State (Ignore slow start phase & No timeouts)
    • Constant packet size

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

achievements tfrc
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
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
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
slide18

Outline

  • Background
  • Classification
  • Achievements
  • Challenges
challenges
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…
slide20

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