TCP Vegas Congestion Control Algorithm

1
TCP Vegas Congestion Control Algorithm

• Mridul Sharma
• CS 590f Project Presentation

2
Contents

• Motivation
• TCP Vegas Congestion Control Algorithm
• Slow Start
• Congestion Avoidance
• Fast Retransmit
• The Problem
• Simulations
• Conclusions

3
Motivation

• Past researches have shown that TCP Vegas is able
  to achieve higher throughput with lesser
  retransmissions than TCP Reno, which is widely
  used in the current internet.
• It is required to consider the migration path for
  TCP Vegas to be deployed in the operating
  network.

4

• Congestion Avoidance
• Expected CWND/BaseRTT
• Actual CWND/RTT
• Diff (Expected Actual) BaseRTT
• CWND CWND 1 if Diff
• CWND CWND 1 if Diff ?
• No change other wise
• Slow Start Congestion Avoidance
• If Diff ?

5
The Problem

• The TCP Reno Congestion avoidance scheme is
  aggressive in the sense that it leaves little
  room in the buffer for other connections, while
  TCP Vegas is conservative and tries to occupy
  little buffer space.
• When a TCP Vegas connection shares a link with
  TCP Reno connection, the TCP Reno connection uses
  most of the buffer space and the TCP Vegas
  connection backs off, interpreting this as a sign
  of network congestion.

6
Conclusions

• It is necessary to achieve fairness between Vegas
  and Reno connections for deployment of TCP Vegas
  into the operating network.
• There are two approaches
• Modify the TCP Vegas congestion Control Algorithm
• Modify the router packet dropping schemes like
  RED to detect misbehaving flows (Reno in this
  case) and punish them more severely.