[e2e] A Framework for Window-based Congestion Control

Nishanth R. Sastry nishanth at cs.utexas.edu
Tue Apr 23 08:24:07 PDT 2002

We would like to report a new mathematical framework called CYRF for
designing congestion control protocols that converge to fairness and
efficiency in the same sense as TCP (and under the same network condition
assumptions as the Chiu-Jain proof for the convergence of TCP). We also
show how to make these flows TCP-friendly.

As an experiment in using this framework, we have developed two protocols
for streaming-media like applications:  LOG, where we balance the need for
smoothness with the need for a fast response to network congestion
indications; and SIGMOID, which is fair to TCP even in the presence of
drop-tail queues (Smooth non-linear window based algorithms such as LOG
and the binomial algorithms are TCP-friendly only with RED queues, which
is a major problem for deployment in the current Internet) by giving up
smoothness in return for a guaranteed minimum throughput.

This framework includes several commonly known protocols such as TCP,
GAIMD and binomial congestion controls as special cases, and thus provides
a common theoretical foundation for window based congestion control. A
second possible application of this framework would use it to derive
results common to all these protocols.

A technical report with details is available for download from

Uncompressed pdf and ps versions of this and other recent technical
reports on congestion control from our group are available from:

We'd greatly appreciate any comments or suggestions.

Sastry, Nishanth R. and Simon S. Lam. "CYRF: A Framework for Window-based
Unicast Congestion Control." The University of Texas at Austin, Department
of Computer Sciences. Technical Report TR-02-09. January 2002. 30 pages.

This work presents a comprehensive theoretical framework of window based
congestion control protocols called CYRF (for Choose Your Response
Function) that are designed to converge to fairness and efficiency. We
first derive a sufficient condition for convergence to fairness. Using
this, we show how fair window increase/decrease policies can be
constructed from suitable pairs of monotonically non-decreasing functions.
We also give a new characterization of TCP-friendliness and simple rules
for smooth CYRF flows to be TCP-friendly. Specific protocols that meet the
needs of a given situation can be designed within this framework. We
experimentally investigate two CYRF protocols for streaming media-like
applications: LOG, a protocol suitable for applications that need to
trade-off between smoothness and aggressiveness, and SIGMOID, which is
designed to be "TCP-friendly" even in a network with drop-tail queues
(unlike other non-linear window based protocols).

- Nishanth

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