Summary: TCP Vegas Review
by Brakmo, O'Malley, and Peterson
Feb 21, 2007
TCP Vegas's main objective is to improve on the TCP implementation that was packaged with
Reno distribution of BSD Unix, specifically by improving throughput by detecting and avoiding
congestion problems. Here are the main contributions of the paper.
· Better round trip time (RTT) estimates (and therefore tighter variances) resulting in better
· Quicker detection of lost segments by inspecting the segment's timestamp rather than waiting
for a course-grained timer to go off to check for timeouts. Checks are made when:
1. duplicate ACKs are received
2. the 1st or 2nd ACK after a retransmission is received
· More careful resizing of the congestion window after a loss, so that the window size is not
reduced multiple times for losses occurring during a single RTT interval.
· Spike suppression to alleviate oversending of data due to ACKs not being evenly spaced.
· Congestion avoidance rather than congestion detection. This is accomplished by calculating
an expected throughput rate equal to the size of the congestion window divided by the
best round trip time seen so far. The expected throughput rate is compared to frequent
measurements of the actual throughput (once per RTT) to adjust the amount of data being