WebTP: Protocol Design Issues

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WebTP Protocol Design Issues

• Jeng Lung Yogesh Bhumralkar

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Introduction

• Following key issues related to the design and
  testing of the protocol
• Congestion Window Control
• Retransmission Timeout Scheme
• Performance under Network Jitter

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Congestion Control

• Background
• WebTP uses TCP-style congestion control
• 2 Phases
• Slow Start
• Congestion Avoidance Additive Increase/Multiplica
  tive Decrease
• TCP biased against long connections therefore,
  WebTP faces same dilemma.

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Improving Fairness

• Maximize fairness by modifying Additive Increase
• Instead of increasing cwnd by 1/cwnd, increase
  it by Kcrttrtt. This makes it more fair
• Problem Find optimal K for fairness
• K is topology dependent but still want to ensure
  that the scheme works for WebTP.

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Network Topology
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Retransmission Scheme

• Current timeout set to
• M is the receivers tolerance to jitter.
• Examine the effects of changing M on the number
  of dropped and duplicate packets.

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Jitter Study

• Any network has considerable random delays.
• The time between when the packet is transmitted
  to when it reaches the receiver varies a great
  deal - this phenomenon is called jitter.
• Simulated jitter by introducing random delay to
  each packet on the sender side.

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Conclusion

• Congestion Window Scheme Optimal K depends on
  network topology.
• Retransmission Scheme Dropped packets increase
  with M whereas the number of duplicate packets
  goes down at higher M.
• Network Jitter Higher jitter implies that a
  higher M is required to handle the delays that
  are introduced.