The Need for Adaptive Routing in the Chaotic and Unbalanced Traffic Environment

By classifying traffic conditions into four categories, we investigate the preference for a deterministic or an adaptive routing strategy with respect to a traffic category. The four categories are: 1) balanced, emulating known and stationary traffic conditions; 2) balanced with surge, emulating a balanced traffic condition with possible unexpected sudden increases in traffic demands between some source-destination pairs; 3) unbalanced, emulating unknown or nonstationary traffic conditions with low to moderate traffic loading; and 4) chaotic, emulating unknown or nonstationary traffic conditions with heavy traffic loading. Our study concludes that a well-chosen deterministic strategy is better for balanced traffic; both deterministic and adaptive procedures are appropriate for balanced traffic with surge; and a well-chosen adaptive strategy is preferred for the unbalanced and chaotic conditions. We also attempt to define a routing strategy that behaves almost deterministically when appropriate and adaptively otherwise. We contend that an adaptive routing strategy with a second-order metric1 + a_{1}Q + a_{2}Q^{2}, where1 \gg a_{1} \gg a_{2}are constants andQis the queue size at a link, is a good compromise. (Values of a1and a2depend on network topology and congestion control strategies.) Our reasoning and results are supported and verified by experimenting with a detailed simulation program.