Why flow-completion time is the right metric for congestion control

Users typically want their flows to complete as quickly as possible: They want a web-page to download quickly, or a file transfer to complete as rapidly as possible. In other words, Flow Completion Time (FCT) is an important - arguably the most important - performance metric for the user. Yet research on congestion control focuses almost entirely on maximizing flow throughput, link utilization and fairness, which matter more to the operator than the user. In this paper we show that existing (TCP Reno) and proposed (XCP) congestion control algorithms make flows last much longer than necessary - often one or two orders of magnitude longer than they need to; and we argue that over time, as the network bandwidth-delay product increases, the discrepancy will get worse. In contrast, we show how a new and practical algorithm - RCP (Rate Control Protocol) - enables flows to complete close to the minimum possible.

• Type: Journal
• Year: 2006
• Where: CCR
• Authors: Nandita Dukkipati, Nick McKeown
• Keywords: CCR 2006, Congestion Control, File Transfer, Flow Completion Time