Congestion control in TCP: performance of binary congestion notification enhanced TCP compared to Reno and Tahoe TCP

In previous work, we proposed to enhance TCP´s congestion control mechanisms using binary congestion notification (BCN). With this combined scheme called BCN-TCP congestion is indicated both by packet losses and by having switches inform sources about their congestion state by setting a congestion bit. Unlike other studies, our approach maintains the basic elements of TCP´s congestion control mechanisms and models the response of TCP to the congestion bit to that of the ATM available bit rate service (ABR). We compared the performance of BCN-TCP to the versions currently implemented in hosts (Tahoe and Reno TCP). However BCN-TCP only offered significant performance improvements if part of the path contained ATM ABR services. In this paper we present further results on the performance of BCN-TCP when used in heterogeneous environments, i.e., Internet paths where only some end systems support BCN-TCP. We also consider the fairness between long and short-haul connections and discover that BCN-TCP treats long-haul connections worse than Tahoe and Reno TCP. We investigate the cause of this unfairness and suggest possible remedies