On Delay Performance of Throughput Optimal Back-pressure Routing: Testbed Results

Maximizing network throughput via back-pressure routing is the subject of a considerable body of literature. It is well known that back-pressure routing induces long delays and this has motivated a number of proposals for improving the delay performance. However, to our knowledge, no useful results are available in the literature that characterize the delays induced by packet re-ordering which is due not only to the nature of back-pressure routing but also to the ubiquity of routing loops. Therefore in this paper we provide a systematic evaluation of basic back-pressure routing algorithm and two of its recently proposed variants on an experimental testbed. This provides the first direct comparison of delay performance. Our findings reveal that even in simple network topologies these algorithms induce extensive routing loops with associated high packet delay.