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Review of Congestion Control for High Bandwidth-Delay Product Networks by Holly Esquivel

Summary: Review of Congestion Control for High Bandwidth-Delay Product Networks
by Holly Esquivel
The authors of this paper present eXplicit Control Protocol (XCP), which can be used as an alternative to
TCP. XCP separates the fairness controller from the efficiency controller to have better control over the
responsiveness of traffic and to decrease oscillation when trying to achieve fairness. It produces an
environment that utilizes max-min fairness to distribute bandwidth. It is responsive in as little as one RTT
when there is an increase or a decrease in the number of flows, and it is able to quickly reach the desired
CWND. It prevents losses by holding packets in queues when the network gets congested and notifies
flows of the congestion via a congestion header on each packet. The header tells the sender how
congested the network is so that it knows how much to back off without wasting network resources from
backing off too much. During each RTT the congestion header is marked so that if more/less bandwidth
becomes available it is quickly deallocated/allocated to other flows. The efficiency controller utilizes the
MIMD protocol while the fairness controller utilizes the AIMD protocol. With each RTT these values are
recalculated so that estimation errors don't cause problems to the system and the end convergence of the
system is stable. Overall, they show that XCP out performs TCP in a variety of settings and it can handle
flows with long RTT times, which is something that TCP can't do. This makes it more feasible than TCP
for use with wireless and satellite links. XCP can also accommodate these flows with long RTT values
while still handling short RTT flows in a fair and efficient manner.


Source: Akella, Aditya - Department of Computer Sciences, University of Wisconsin at Madison


Collections: Computer Technologies and Information Sciences