'Institute of Electrical and Electronics Engineers (IEEE)'
Doi
Abstract
Cataloged from PDF version of article.We analyze the performance of the CSMA protocol
under propagation delays that are comparable with packet
transmission times. We propose a semi-Markov model for the
2-node CSMA channel. For the 2-node case, the capacity reduces
to 40% of the zero-delay capacity when the one-way propagation
delay is 10% of the packet transmission time. We then extend
this model and obtain the optimum symmetric probing rate
that achieves the maximum network throughput as a function
of the average propagation delay, d¯, and the number of nodes
sharing the channel, N. The proposed model predicts that the
total capacity decreases with d¯−1 as N goes to infinity when
all nodes probe the channel at the optimum rate. The optimum
probing rate for each node decreases with 1/N and the total
optimum probing rate decreases faster than d¯−1 as N goes to
infinity. We investigate how the short-term unfairness problem in
CSMA worsens as the propagation delay increases and propose a
back-off mechanism to mitigate this issue. The theoretical results
presented in this paper can be used as a benchmark for the
performance improvements provided by algorithms that have
already been developed