MCP: Few Bits for Fairing and Small Queues in the Stable State

Interactive and other delay-sensitive applications are interested in keeping end-to-end delays of their packets minimal. Unfortunately, congestion control offered by transmission control protocol (TCP) and other existing protocols inflates the end-to-end delays by building up queues at bottleneck links. In this paper, we investigate multimodal control protocol (MCP) designed to maintain low queues after converging to the stable state where MCP flows utilize shared bottleneck links efficiently and fairly. To achieve this goal, MCP incorporates multiple modes of operation and allocates few bits in each packet header for explicit communication between hosts and routers. An innovative aspect of the explicit communication mechanism is an ability of a flow to urge all flows on its bottleneck links to switch temporarily into a fairing mode and thereby improve fairness of the bottleneck sharing. To make the fair sharing independent of round-trip times and packet sizes, MCP uses the sending bitrate as a control parameter and employs uniform adjustment timing for all flows. Our evaluation of MCP demonstrates its efficient fair operation and significantly shorter stable-state queues than under existing congestion control protocols.