[Colloq] PhD Thesis Defense **Tuesday, May 20, 2003**

[Rachel Bates]

Date: Tuesday, May 20
Time: 1:00 - 2:30 PM
Place: 149 Cullinane Hall

Ph.D. Thesis Defense

Title: Receiver-oriented and Measurement-based Transmission Control
       in Heterogeneous (Wired/Wireless) Networks

by:
Chi Zhang

Advisor: Vassilis Tsaoussidis
Committee: Gene Cooperman, Paul Attie
External Committee Member :Ioanis Nikolaidis (U. of Alberta), Ibrahim Matta
(BU)


Abstract

While TCP congestion control is appropriate for applications such as bulk
data transfer over wired networks, its somewhat "blind" AIMD
window-adjustment strategy degrades the throughput over wireless networks
and damages the real-time performance of delay-sensitive applications. In
this talk, I will present my research on transport mechanisms for the next
generation internet.

I will first investigate the interrelation of TCP smoothness and
responsiveness by studying the combined dynamics of friendliness-oriented
alpha/beta tradeoff. I will demonstrate that equation-based transmission
adjustments could guarantee neither efficiency nor friendliness on its
own, in heterogeneous or dynamic environments.

I will then introduce TCP Real, which employs a receiver-oriented and
measurement-based congestion control mechanism that significantly improves
TCP performance in heterogeneous networks.

Finally, I will discuss a synchronized and measurement-based congestion
avoidance mechanism that improves TCP smoothness for real-time
applications. We argue that the major obstacle for achieving smoothness is
the unsynchronized multiplicative decreases due to random congestive
drops.  The novel mechanism coordinates upward and backward adjustments to
abolish the damage of unsynchronized window control. Congestive packet
drops are reduced by a new control parameter, and the bottleneck queue
length can also be controlled in an end-to-end manner.