Trail blazer: a routing algorithm inspired by ants

We propose a new intra-domain IP routing algorithm called trail blazer (TB) that alleviates network congestion by local decisions based on latency measurements collected by scout packets. TB is a member of a class of traffic-aware routing algorithms based on the behavior of ants. TB maintains in every router a probability table that controls the selection of outgoing links for a given destination. This table is modified by passing scout packets. Some scout packets follow existing high probability paths, and other scout packets explore new paths by making random "mistakes" in order to find detours around congested areas of the network. Scout packets do not have global knowledge of the network topology. Rather, they are influenced by probability trails left by previous scout packets, and leave a trail of updated probability information. TB is meant to be an extension of existing link-state protocols such as OSPF or IS-IS, which provide shortest-path information to initialize the probability table. Simulations of UDP traffic in congested networks show a reduction of packet drops by factors of 3.4-38.4 and 1.8-8.2, for single-path and multi-path shortest-path routing, respectively, with a bounded reordering window. Even though TB may cause packet reordering which may affect the congesting control mechanisms of TCP, TCP traffic sent over TB has a similar bandwidth to shortest-path routing. Simulation of a hybrid routing algorithm that routes TCP traffic over shortest paths and UDP traffic over TB show reduced interference between TCP and UDP traffic.