|
Most of the Web traffic today uses the HyperText Transfer
Protocol(HTTP), with the Transmission Control Protocol
(TCP) as the underlying transport protocol. TCP provides several
important services to HTTP, including reliable data transfer and
congestion control. 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
man-ner, 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 net-work parameters (i.e., packet loss rates) on the
performance of the hybrid scheme. We observed perfor-mance gains
exceeding 20-250 with HTTP/1.1-style persistent connections, and over
40-500 without persistent connections. These gains can be improved
with further performance optimizations that we describe.
|
