Towards a Queue Sensitilve Transport Protocol

The TCP NewReno congestion control protocol relies only on packer losses for detecting congestion-this causes long NewReno transfers to build up large packet queues in router buffers. High buffer occupancy hinders performance of real-time applications as well as the development of high-speed routers. Several alternate congestion-control strategies have been proposed in the literature to help maintain low buffer occupancy. In this paper, we experimentally evaluate prominent proposals by emulating empirically-derived traffic mixes on a Linux-based lab testbed. We show that when existing proposals are used with such representative traffic mixes, they are unable to simultaneously ensure small router queues and high TCP throughput. Further analysis shows that the common practice of using TCP round-trip times for estimating queuing delays (as in TCP Vegas) fails in a highly-aggregated environment that contains short as well as long transfers' such environments would need to rely on explicit router feedback. We also find that proposals that rely on router feedback in the form of link utilization (as recently proposed in VCP) are not effective in maintaining high transfer throughput. Instead, we argue that a congestion control algorithm which used queuing delay feedback from routers can reduce the buffer occupancy of routers without sacrificing response time performance of connections. We use this idea to design two new protocals-EDN and PEDN-and show that these two protocols can help manage the trade-off between maintaining low buffer occupancy and providing high TCP throughput.