TCP revisited: A fresh look at TCP in the wild

Feng Qian, Alexandre Gerber, Z. Morley Mao, Subhabrata Sen, Oliver Spatscheck, Walter Willinger

Research output: Chapter in Book/Report/Conference proceedingConference contribution

52 Scopus citations


Since the last in-depth studies of measured TCP traffic some 6- 8 years ago, the Internet has experienced significant changes, including the rapid deployment of backbone links with 1-2 orders of magnitude more capacity, the emergence of bandwidth-intensive streaming applications, and the massive penetration of new TCP variants. These and other changes beg the question whether the characteristics of measured TCP traffic in today's Internet reflect these changes or have largely remained the same. To answer this question, we collected and analyzed packet traces from a number of Internet backbone and access links, focused on the "heavy-hitter" flows responsible for the majority of traffic. Next we analyzed their within-flow packet dynamics, and observed the following features: (1) in one of our datasets, up to 15.8% of flows have an initial congestion window (ICW) size larger than the upper bound specified by RFC 3390. (2) Among flows that encounter retransmission rates of more than 10%, 5% of them exhibit irregular retransmission behavior where the sender does not slow down its sending rate during retransmissions. (3) TCP flow clocking (i.e., regular spacing between flights of packets) can be caused by both RTT and non-RTT factors such as application or link layer, and 60% of flows studied show no pronounced flow clocking. To arrive at these findings, we developed novel techniques for analyzing unidirectional TCP flows, including a technique for inferring ICW size, a method for detecting irregular retransmissions, and a new approach for accurately extracting flow clocks.

Original languageEnglish (US)
Title of host publicationIMC 2009 - Proceedings of the 2009 ACM SIGCOMM Internet Measurement Conference
Number of pages14
StatePublished - Dec 1 2009
Externally publishedYes
Event2009 9th ACM SIGCOMM Internet Measurement Conference, IMC 2009 - Chicago, IL, United States
Duration: Nov 4 2009Nov 6 2009

Publication series

NameProceedings of the ACM SIGCOMM Internet Measurement Conference, IMC


Other2009 9th ACM SIGCOMM Internet Measurement Conference, IMC 2009
Country/TerritoryUnited States
CityChicago, IL


  • Network measurement
  • TCP


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