MPAT: aggregate TCP congestion management as a building block for Internet QoS

Today Internet QoS is deployed piecemeal - typically at known bottleneck links like enterprise access links or wireless links. A more comprehensive, end-to-end QoS deployment, for instance across large enterprise networks or the global Internet, remains elusive. There is growing interest in the idea of using overlay networks to provide differential QoS services (improve performance for some flows at the expense of other flows). A necessary building block is the ability to provide differential service over a single overlay link that traverses many IP router hops. This work presents MPAT, the first truly scalable algorithm for fairly providing differential services to TCP flows that share a bottleneck link. Unlike known schemes, our approach preserves the cumulative fair share of the aggregated flows even where the number of flows in the aggregate is large. Specifically we demonstrate, primarily through experiments on the real Internet, that congestion state can be shared across more than 100 TCP flows with throughput differentials of 95:1. This is up to five times better than differentials achievable by known techniques. Indeed, MPAT scalability is limited only by the delay-bandwidth product of the aggregated flows. With this tool, it is now possible to seriously explore the viability of network QoS through overlay network services.