A Control-Theoretic Approach to Flow Control

                          Srinivasan Keshav
            Computer Science Division, Department of EECS,
                 University of California, Berkeley,
                                 and
               International Computer Science Institute
                          Berkeley, CA 94720
                   email: keshav@tenet.berkeley.edu





                               ABSTRACT
This paper presents a control-theoretic approach to reactive flow con-
trol  in  networks  that  do not reserve bandwidth. We assume a round-
robin-like queue service  discipline  in  the  output  queues  of  the
network's  switches,  and  propose deterministic and stochastic models
for a single conversation in a network of such switches. These  models
motivate the Packet-Pair rate probing technique, and a provably stable
rate-based flow control scheme. A Kalman state  estimator  is  derived
from discrete-time state space analysis, but there are difficulties in
using the estimator in practice.  These difficulties are overcome by a
novel  estimation scheme based on fuzzy logic. We then present a tech-
nique to extract and use additional information  from  the  system  to
develop a continuous-time system model. This is used to design a vari-
ant of the control law that is also provably stable, and, in addition,
takes control action as rapidly as possible. Finally, practical issues
such as correcting parameter drift and coordination with  window  flow
control are described.