Congestion Control for High Bandwidth-Delay Product Networks

Theory and experiments show that as the per-flow product of band-width and latency increases, TCP becomes inefficient and prone to instability, regardless of the queuing scheme. This failing becomes increasingly important as the Internet evolves to incorporate very high-bandwidth optical links and more large-delay satellite links. To address this problem, we develop a novel approach to Inter-net congestion control that outperforms TCP in conventional en-vironments, and remains efficient, fair, scalable, and stable as the bandwidth-delay product increases. This new eXplicit Control Pro-tocol, XCP, generalizes the Explicit Congestion Notification pro-posal (ECN). In addition, XCP introduces the new concept of de-coupling utilization control from fairness control. This allows a more flexible and analytically tractable protocol design and opens new avenues for service differentiation. Using a control theory framework, we model XCP and demon-strate it is stable and efficient regardless of the link capacity, the round trip delay, and the number of sources. Extensive packet-level simulations show that XCP outperforms TCP in both conventional and high bandwidth-delay environments. Further, XCP achieves fair bandwidth allocation, high utilization, small standing queue size, and near-zero packet drops, with both steady and highly vary-ing traffic. Additionally, the new protocol does not maintain any per-flow state in routers and requires few CPU cycles per packet, which makes it implementable in high-speed routers