Resynchronization and controllability of bursty service requests

There is an increasing prevalence of interactive Web sessions in the Internet. These are mostly short-lived TCP connections that are delay-sensitive and have transfer times dominated by TCP backoffs, if any, during connection establishment. Unfortunately, arrivals of such connections at a server tend to be bursty, and can trigger multiple retransmissions, resulting in long average client-perceived delays. Traditional traffic control mechanisms, such as token bucket filters, are designed to complement admission control mechanisms, by regulating throughput, bounding service times, and protecting systems from overload. However, they cannot control connection-establishment delays, and thus, do not provide effective control of client-perceived delays. We first present the surprising discovery of a resynchronization property of retransmitted requests that exacerbates client-perceived delays when traditional control mechanisms are used. Then, we introduce a novel, multistage filtering scheme called Abacus Filters (AFs) that limits the client-perceived delay while maximizing server throughput even in the case of bursty connection arrivals. Analysis of delay-control properties of various filtering mechanisms is presented, along with a detailed performance evaluation. AFs are shown to provide tight delay control and better complement traditional admission control policies.