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TCP's Initial Window –- Deployment in the Wild and its Impact on Performance

Rüth, Jan and Kunze, Ike and Hohlfeld, Oliver (2019):
TCP's Initial Window –- Deployment in the Wild and its Impact on Performance.
In: IEEE Transactions on Network and Service Management, DOI: 10.1109/TNSM.2019.2896335, [Article]

Abstract

TCP congestion control and particularly its initial congestion window (IW) size is one long-debated topic that can influence web performance. Its size is, however, assumed to be static by IETF recommendations—despite being network-and application-dependent—and only infrequently changed in its history. To understand if the standardization and research perspective still meets Internet reality, we study the IW configurations in IPv4 and of major content delivery networks (CDNs). We have been regularly inspecting IPv4 for HTTP and TLS servers to investigate their IW configuration and found a steady increase in IETF-recommended configurations. We additionally study how CDNs configure their IWs given their relevance for content distribution. To shed light on network-dependent CDN configurations, we use a globally distributed infrastructure of VPNs giving access to residential access links. We observe that most CDNs are well aware of the IW’s impact and find a high amount of customization that is beyond current Internet standards. We find various initial window configurations, most below 50 segments, yet, with exceptions of up to 100 segments—the tenfold of current standards. Our study highlights that Internet reality has drifted away from recommended and standardized practices. Driven by these findings, we investigate the effects of this new reality on the slow start of Cubic and BBR congestion controlled TCP flows. We find that TCP pacing is a key to enable increased IWs when competing against other traffic.

Item Type: Article
Erschienen: 2019
Creators: Rüth, Jan and Kunze, Ike and Hohlfeld, Oliver
Title: TCP's Initial Window –- Deployment in the Wild and its Impact on Performance
Language: German
Abstract:

TCP congestion control and particularly its initial congestion window (IW) size is one long-debated topic that can influence web performance. Its size is, however, assumed to be static by IETF recommendations—despite being network-and application-dependent—and only infrequently changed in its history. To understand if the standardization and research perspective still meets Internet reality, we study the IW configurations in IPv4 and of major content delivery networks (CDNs). We have been regularly inspecting IPv4 for HTTP and TLS servers to investigate their IW configuration and found a steady increase in IETF-recommended configurations. We additionally study how CDNs configure their IWs given their relevance for content distribution. To shed light on network-dependent CDN configurations, we use a globally distributed infrastructure of VPNs giving access to residential access links. We observe that most CDNs are well aware of the IW’s impact and find a high amount of customization that is beyond current Internet standards. We find various initial window configurations, most below 50 segments, yet, with exceptions of up to 100 segments—the tenfold of current standards. Our study highlights that Internet reality has drifted away from recommended and standardized practices. Driven by these findings, we investigate the effects of this new reality on the slow start of Cubic and BBR congestion controlled TCP flows. We find that TCP pacing is a key to enable increased IWs when competing against other traffic.

Journal or Publication Title: IEEE Transactions on Network and Service Management
Divisions: DFG-Collaborative Research Centres (incl. Transregio)
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 1053: MAKI – Multi-Mechanisms Adaptation for the Future Internet
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 1053: MAKI – Multi-Mechanisms Adaptation for the Future Internet > B: Adaptation Mechanisms
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 1053: MAKI – Multi-Mechanisms Adaptation for the Future Internet > B: Adaptation Mechanisms > Subpproject B1: Monitoring and Analysis
Date Deposited: 18 Feb 2019 13:31
DOI: 10.1109/TNSM.2019.2896335
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