TCP/IP and HIPPI Performance in the CASA Gigabit Testbed
Bilal Chinoy Kevin Fall **
San Diego Supercomputer Center San Diego Supercomputer Center y
bac@sdsc.edu kfall@cs.ucsd.edu
Abstract
We investigate the packet delay and loss characteristics of the
wide-area HIPPI-based CASA gigabit testbed. Developed for high--speed
local area device interconnects, HIPPI is a point--to--point,
connection--oriented protocol. We show HIPPI blocking can degrade
performance by increasing delay and/or packet loss. In the CASA
network under conditions of blocking, a tradeoff exists between packet
loss and delay variance. The tradeoff point is determined by a
combination of factors: source packet rate, mean blocking rate, and a
configurable connection establishment timeout threshold. We show the
delay/loss tradeoff manifests itself in TCP as inducing either the
slow-start algorithm or requiring TCP to adjust retransmission timeout
values due to increased delay variance. In the former case, we have
measured TCP throughput to drop by as much as 97% of its unblocked
maximum, as compared with 75% for the latter case.
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