Subject: TCP over lossy links

From: Alhussein Abouzeid <[email-masked]>
Date: Thu, 26 Oct 2000 14:39:32 -0700 (PDT)

Hi,

Enclosed is an abstract of a paper (submitted to ToN, Jan. 2000)
re analytical modeling of TCP performance in the presence of 
wireless links, i.e. random, correlated-loss environments. 
This is an extension to our Infocom 2000 paper (available at URL below)  
that attempts to faithfully capture the interplay
between TCP's congestion control algorithm, the channel induced loss behavior and
the dynamics of the transmit queue. 

The primary contribution of the work is modeling the impact of
all the following on TCP performance: 

1. The two modes of packet loss detection: triple duplicates as
well as timeouts and the binary exponential backoff;
2. The variation of the RTT due to queuing;
3. The two congestion avoidance phases of TCP;
4. Channel induced i.i.d and/or correlated loss in addition to possible
packet loss due to buffer overflow.

The papers can be downloaded at

http://students.washington.edu/abouzeid/research.htm

As usual, all comments are greatly appreciated.

Best regards,

Alhussein A. Abouzeid.
 ---------------------------------

 	A Unified Approach to Modeling TCP Performance Over a Lossy Link

                 Alhussein A. Abouzeid, Sumit Roy and Murat Azizoglu
                    Dept. of Electrical Engineering
                    Univ. of Washington Box 352500
                    Seattle, WA 98195

Abstract:

A new, comprehensive analytical framework for modeling the long-term
performance of a single TCP session in the presence of random packet loss
is  presented.
A Markovian model is developed for both memoryless channels (independent,
identically distributed packet loss) and channels with memory (correlated
packet loss) modeled by a two state  continuous time 
Gilbert-Elliott model.
The analytical results (throughput) are validated against those obtained
from ns simulator and shows very good agreement for a wide
range of network  parameters - i.e., low (LANs) and
high (WANs) bandwidth-delay products. Further, the  
throughput for the i.i.d. loss model is found to be relatively 
insensitive to the probability density function (p.d.f) of the loss 
inter-arrival process.
For channels with memory, an empirical rule is presented 
for categorizing the impact of channel dynamics (fading rate) on TCP
performance.