A Distributed Algorithm for Throughput Optimal Routing in Overlay Networks

We address the problem of optimal routing in overlay networks. An overlay network is constructed by adding new overlay nodes on top of a legacy network. The overlay nodes are capable of implementing any dynamic routing policy, however, the legacy underlay has a fixed, single path routing scheme and uses a simple work-conserving forwarding policy. Moreover, the underlay routes are pre-determined and unknown to the overlay network. The overlay network can increase the achievable throughput of the legacy network by using multiple routes, which consist of direct routes and indirect routes through other overlay nodes. We develop an optimal dynamic routing algorithm for such overlay networks called the Optimal Overlay Routing Policy (OORP). OORP is derived using the classical dual subgradient descent method, and it can be implemented in a distributed manner. We show that the queue-lengths can be used as a substitute for the dual variables in the algorithm. However, the underlay queue-lengths are unknown to the overlay, so we propose two regression based schemes that learn simplified models of the backlog in the underlay using historical data and use them to estimate the queue-lengths in real time. Simulation results show that near-optimal performance can be achieved without any knowledge of the underlay.