1. TCP Vegas Congestion Control Algorithm
Mridul Sharma
CS 590f Project Presentation

2. Contents Motivation TCP Vegas Congestion Control Algorithm The Problem
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.