Understanding asymmetric links, buffers and bi-directional TCP performance.

摘要

Asymmetric uplink and downlink rates are common in many broadband access networks, particularly DSL, DOCSIS, and cellular. With the advent of peer-to-peer protocols and pervasive devices supporting multimedia capabilities, bi-directional TCP traffic has also become commonplace [1]. Under conditions where TCP connections are sending data in both directions simultaneously, performance, as we will show, can be severely degraded.;This thesis seeks to determine how buffers, combined with elementary queueing strategies like FIFO, influence bi-directional TCP performance across asymmetric network links. It also seeks to determine if there is a way to size buffers such that the throughput for a small number of bi-directional connections is optimized.;To answer this question, fundamental system components and algorithms will be reviewed. Following this, research pertaining to observations, optimization techniques and design spaces will be analyzed. Next, a set of real world experiments will be analyzed. Finally, a buffer sizing model will be proposed that optimizes throughput for the bi-directional, long lived, TCP traffic under a FIFO queueing strategy.;Practically speaking, this thesis seeks to determine if current consumer grade customer premise equipment is designed to provide adequate performance for bi-directional Internet traffic across typical asymmetric access technologies like DSL and DOCSIS.