TUF: tag-based unified fairness

Finding an appropriate end-to-end congestion control scheme for each type of flow, such as real-time or multicast flows, may be difficult. But it becomes even more complex to have these schemes be friendly among themselves and with TCP. The assistance of routers within the network for fair bandwidth sharing among the flows is therefore helpful. However, most of the existing mechanisms that provide this fair sharing imply complex buffer management and maintaining flow state in the routers. We propose to realize this fair bandwidth sharing without per-flow state in the routers, using only a trivial queueing discipline. Packets are tagged near the source, depending on the nature of the flow. In the core of the network, routers use FIFO queues, and simply drop the packet with the highest tag value in case of congestion. Contrarily to other stateless fair queueing algorithms in the core routers, we do not try to maintain instantaneous flow rates equal. Instead, we take into account the responsiveness nature of the flows, and adjust loss rates such that average rates are equal. The novel approach of our scheme, called TUF, tag-based unified fairness, not only improves the overall fairness but enables us to maintain it in realistic environments, with non-negligible round trip times or bursty traffic, where other schemes fail. The corresponding cost is the need for models of the end to-end responsive natures of the flows.