Rate adaptive packet dropping scheme for TCP traffic over rate-controlled links

We study a gateway congestion control scheme for TCP traffic in an internetwork consisting of both rate-controlled and non-rate-controlled links. In this network scenario, TCP window-based congestion control and rate-based congestion control at a rate-controlled link may not interact in a harmonious way. So, we present a packet dropping scheme called rate adaptive dropping (RAD) as a means for reconciling the mismatch between window-based and rate-based congestion controls. The main idea of RAD is to drop arriving packets depending on the rate feedback information so that dropped packets may notify TCP sources of incipient congestion before the gateway buffer overflows. We compare the performance of RAD with that of tail drop in terms of goodput and drop ratio. Results from simulations show that RAD achieves significant improvements over tail drop, especially when the gateway buffer size is around the bandwidth delay product or less.