On the throughput and fairness performance of TCP over Ethernet Passive Optical Networks

The Ethernet Passive Optical Network (EPON) is a promising solution for metropolitan optical networks. In EPON, the downstream channel is a point-to-multipoint broadcast network and the upstream channel is a multipoint-to-point network based on a polling mechanism. In this paper, we model the performance of TCP over EPON with respect to the aggregate throughput and fairness. We calculate the maximum aggregate throughput of TCP flows on each of the upstream and downstream channels, and identify the fairness problem with existing polling schemes for EPON. We then derive two tight bounds of the fairness index for downloading users, and propose two polling mechanisms to improve unfair resource sharing among multiple TCP flows. The performance of the proposed mechanisms is evaluated via ns-2 simulations. The results show that our mechanisms can improve fairness among downloading TCP flows without degrading the aggregate throughput and fairness of uploading TCP flows.