Hybrid TCP-UDP transport for Web traffic

Abstract

Most of the web traffic today uses the HyperText Transfer Protocol (HTTP), with Transmission Control Protocol (TCP) as the underlying transport protocol. Unfortunately, TCP is poorly suited for the short conversations that comprise a significant component of web traffic. The overhead of setting up and tearing down TCP state amortizes poorly for these small connections. Moreover, emerging modern web server systems employ HTTP redirection for server load-balancing and content distribution; such schemes require setting up (and tearing down) multiple TCP connections for servicing a single client request. We have designed and analyzed a hybrid scheme to address these issues. The scheme uses either TCP, or the User Datagram Protocol (UDP) as the underlying transport protocol for carrying web traffic. UDP is used for short transfers (including HTTP redirection), while TCP is used for all other transfers. In this manner, we avoid the extra TCP overhead for short connections, but still benefit from the reliable delivery and congestion control that TCP provides. We ran trace-based simulations to quantify the effects of various network parameters (i.e., packet loss rates) on the performance of the hybrid scheme. We observed performance gains exceeding 20-25% with HTTP/1.1-style persistent connections, and over 40-50% without persistent connections. These gains can be improved with further performance optimizations that we describe.