A Markovian Model for TCP Analysis in a Differentiated Services Network

In a Differentiated Services network, the use of TCP by an application impacts the service it gets from the network. TCP congestion control algorithms are designed to provide a fair sharing of resources in a best effort network as the current Internet. TCP is not conscious of the new services proposed by DiffServ, namely the different priorities packets are injected with into the network. Many schemes have been proposed to support TCP traffic in a DiffServ network. These schemes have been often validated with simulations. In this paper we propose an analytical model to study the performance of TCP in a DiffServ network under the different proposed schemes. The model is based on a Markovian fluid approach. We present first a general version of the model, then we specify it to the different proposed schemes. For each scheme, we compute the throughput achieved by a TCP connection. We compare then the service differentiation provided by the proposed schemes under different subscription levels, different reservations, and different round-trip times. Our model forms a good tool for the evaluation of new solutions to support TCP traffic in a DiffServ network.