Combining Multipath Routing and Congestion Control for Robustness

Flexible routing schemes mitigate some of the problems associated with uncertain traffic patterns and workloads by making the exact location of capacity less important: if there is available capacity the routing scheme will find it. In this paper we propose a combined multipath routing and congestion control architecture that can provide performance improvements to the end user and simplifies network dimensioning for operators. We describe a flow-level model, able to handle streaming and file transfer traffic, with stochastic arrivals, and look at a fluid limit. We describe a congestion controller and path selection algorithm that automatically balances traffic across the lowest cost paths, and we suggest ways in which just two paths may be used, with a random selection policy. A notable feature of a multipath congestion controller is that it cannot be tuned to a single RTT, hence it differs from standard TCP with respect to RTT bias. We show that under certain conditions the allocation of flows to paths is optimal and independent of the flow control algorithm used. Scalability of the architecture results from implementing the algorithms at end-systems. We illustrate by examples how such an approach can halve response times and double the load that a network can carry.