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

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

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.

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 > 

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.

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.