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Unformatted text preview: Internet Congestion Control for Future High Bandwidth-Delay Product Environments Dina Katabi Mark Handley Charlie Rohrs MIT-LCS ICSI Tellabs firstname.lastname@example.org email@example.com firstname.lastname@example.org Abstract Theory and experiments show that as the per-flow product of bandwidth 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 Internet congestion control that outperforms TCP in conven- tional environments, and remains efficient, fair, scalable, and stable as the bandwidth-delay product increases. This new eXplicit Control Protocol, XCP, generalizes the Explicit Con- gestion Notification proposal (ECN). In addition, XCP intro- duces the new concept of decoupling 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 demonstrate it is stable and efficient regardless of the link ca- pacity, the round trip delay, and the number of sources. Ex- tensive packet-level simulations show that XCP outperforms TCP in both conventional and high bandwidth-delay environ- ments. Further, XCP achieves fair bandwidth allocation, high utilization, small standing queue size, and near-zero packet drops, with both steady and highly varying traffic. Addition- ally, 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. 1 Introduction For the Internet to continue to thrive, its congestion control mechanism must remain effective as the network evolves. Technology trends indicate that the future Internet will have a large number of very high-bandwidth links. Less ubiqui- tous but still commonplace will be satellite and wireless links with high latency. These trends are problematic because TCP reacts adversely to increases in bandwidth or delay. Mathematical analysis of current congestion control al- gorithms reveals that, regardless of the queuing scheme, as the delay-bandwidth product increases, TCP becomes more oscillatory and prone to instability. By casting the problem into a control theory framework, Low et al.  show that as capacity or delay increases, Random Early Discard (RED) , Random Early Marking (REM) , Proportional Inte- gral Controller , and Virtual Queue  all eventually become prone to instability. They further argue that it is un- likely that any Active Queue Management scheme (AQM) can maintain stability over very high-capacity or large-delay links. Although their analysis uses Reno TCP, their argument is valid for all current TCP implementations where through- put is inversely proportional to the round trip time (RTT) and the square root of the drop rate. Furthermore, Katabi andthe square root of the drop rate....
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- Spring '08