A Stochastic Model of TCP Reno Congestion Avoidance and Control

Jitendra Padhye, Victor Firoiu and Don Towsley

Department of Computer Science
University of Massachusetts
Amherst MA  01003

Abstract:
The steady state performance of a bulk transfer TCP flow (i.e. a flow with 
a large amount of data to send, such as FTP transfers) may be characterized
by three quantities. The first is the {\em send rate}, which is the
amount of data sent by the sender in unit time. The second is the
$throughput$, which is the amount of data received by the receiver
in unit time. Note that the throughput will always be less than or equal
to the send rate due to losses. Finally, the number of non-duplicate
packets received by the receiver in unit time give us the $goodput$ of
the connection. The goodput is always less than or equal to
the throughput, since the receiver may receiver two copies of the same
packet due to retransmissions by the sender. In [1] we presented a simple 
model for predicting the steady state send rate of a bulk transfer TCP flow 
as a function of loss rate and round trip time. In this paper, we extend that 
work in two ways. First, we analyze the performance of bulk transfer TCP 
flows using more precise, stochastic analysis. We show that the predictions 
of the approximate model in [1] closely match the predictions of the more 
precise model, thus validating the approximate model. Second, we build upon the 
analysis in [1] to provide both an approximate formula 
as well as a more accurate stochastic model for the steady state throughput 
of a bulk transfer TCP flow.

References:
[1] J. Padhye, V. Firoiu, D. Towsley and J. Kurose. Modeling TCP
Throughput: A Simple Model and its Empirical Validation. In Proccedings
of SIGCOMM'98