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Jongwon Yoon TCP Vegas: New techniques for congestion detection and avoidance

Summary: Jongwon Yoon
TCP Vegas: New techniques for congestion detection and avoidance
This paper proposed modifications to TCP, called TCP Vegas, to achieve better
throughput and reduce the loss rate. From the simulation results, Vegas improves 50%
on throughput, and only half the losses compared to TCP Reno. There are five
techniques Vegas uses to improve the performance.
First, to calculate the RTT more accurately, Vegas uses system clock each time a
segment is sent and ACK is arrived. Second, Vegas extends the duplicate ACK
mechanism not to wait longer than necessary. Vegas retransmits the segment without
having to wait for n duplicate ACKs using timestamps. Third, Reno doesn't adequately
decrease the congestion window. However, Vegas only decreases the congestion
window size due to the current loss and detects the loss better than Reno. Forth, many
Reno losses are due to a failure in the self-clocking mechanism that result in spikes in
the sending rate. Vegas allows twice max-segment bytes on each segment spacing
interval to suppress the spikes. Finally, Vegas detects the congestion at the incipient
stages by proactive manner and maintains the right amount of extra data in the network.
Vegas uses RTT value to measure the expected throughput and compare it to the
actual current data to adjust the window size accordingly. For slow-start, Vegas allows
exponential growth every other RTT and keeps the congestion window fixed in between
so a valid comparison of the expected and actual rates can be made. When the actual


Source: Akella, Aditya - Department of Computer Sciences, University of Wisconsin at Madison


Collections: Computer Technologies and Information Sciences