Hi all!
This is the technical report I referred to on this thread. The
report investigates if there exists a strong correlation between the number of
packets in flight and the round trip time. The correlation exists, but is
not strong enough to insure the success of techniques like TCP-Vegas. The
correlation is not strong enough to build "smart" congestion avoidance
techniques which relate the number of packets in flights and the round
trip time. The study is based on the data set N2 collected by Vern Paxson
for his Ph.D thesis.
The paper can be found at :
http://www.cs.tamu.edu/people/saadb/tech99-006.ps
Your comments will be the most welcome !
Title : "Is the Round-trip Time Correlated with the Number of Packets
in Flight ? "
Abstract :
TCP uses packet loss as a feedback from the network to adapt
its sending rate. TCP keeps increasing its sending rate regardless of the
network congestion state as long as no loss occurs (unless constrained
by buffer size).
Alternative congestion avoidance techniques (CATs) have been proposed
to avoid such ``agressive'' behavior. These CATs use simple statistics
on observed round-trip times and/or throughput of a TCP connection in
response to variations in congestion window size.
These CATs have a supposed ability to detect queue build-up. Such ability
may be used to distinghish congestion losses from transmission losses. A
previous study shows that these CATs do not yield interesting results for
diagnosing the real reason of a loss.
The objective of this paper is to question the ability of these
CATs to reliably detect queue build-up under real network conditions.
For this purpose, we analyze the sample coefficient of
correlation between round-trip time and the number of packets in flight
for 14,218 connections over 737 Internet paths. These coefficients of
correlation were extracted from a set of {\em tcpdump} traces collected by
Vern Paxson.
___________________________________________________________________
Saad Biaz (Abou Youssef & Rim) Lecturer
Texas A&M University Office : (409) 845-5007
Department of Computer Science Home : (409) 862-9135
College Station, TX, 77843-3112 Fax : (409) 847-8578
___________________________________________________________________
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