draft-ietf-tcpm-initcwnd-07.txt   draft-ietf-tcpm-initcwnd-08.txt 
Internet Draft J. Chu Internet Draft J. Chu
draft-ietf-tcpm-initcwnd-07.txt N. Dukkipati draft-ietf-tcpm-initcwnd-08.txt N. Dukkipati
Intended status: Experimental Y. Cheng Intended status: Experimental Y. Cheng
M. Mathis M. Mathis
Expiration date: July 2013 Google, Inc. Expiration date: August 2013 Google, Inc.
January 28, 2013 February 22, 2013
Increasing TCP's Initial Window Increasing TCP's Initial Window
Status of this Memo Status of this Memo
Distribution of this memo is unlimited. Distribution of this memo is unlimited.
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
This Internet-Draft will expire on May, 2013. This Internet-Draft will expire on August, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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IETF TCP Maintenance and Minor Extensions (TCPM) working group. IETF TCP Maintenance and Minor Extensions (TCPM) working group.
Terminology Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. TCP Modification . . . . . . . . . . . . . . . . . . . . . . . 4 2. TCP Modification . . . . . . . . . . . . . . . . . . . . . . . 4
3. Implementation Issues . . . . . . . . . . . . . . . . . . . . 5 3. Implementation Issues . . . . . . . . . . . . . . . . . . . . . 5
4. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Advantages of Larger Initial Windows . . . . . . . . . . . . . 7 5. Advantages of Larger Initial Windows . . . . . . . . . . . . . 7
5.1 Reducing Latency . . . . . . . . . . . . . . . . . . . . . . 7 5.1 Reducing Latency . . . . . . . . . . . . . . . . . . . . . . 7
5.2 Keeping up with the growth of web object size . . . . . . . 8 5.2 Keeping up with the growth of web object size . . . . . . . 8
5.3 Recovering faster from loss on under-utilized or wireless 5.3 Recovering faster from loss on under-utilized or wireless
links . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 links . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Disadvantages of Larger Initial Windows for the Network . . . 9 7. Disadvantages of Larger Initial Windows for the Network . . . . 9
8. Mitigation of Negative Impact . . . . . . . . . . . . . . . . 10 8. Mitigation of Negative Impact . . . . . . . . . . . . . . . . 10
9. Interactions with the Retransmission Timer . . . . . . . . . . 10 9. Interactions with the Retransmission Timer . . . . . . . . . 10
10. Experimental Results From Large Scale Cluster Tests . . . . . 10 10. Experimental Results From Large Scale Cluster Tests . . . . . 10
10.1 The benefits . . . . . . . . . . . . . . . . . . . . . . . 11 10.1 The benefits . . . . . . . . . . . . . . . . . . . . . . 11
10.2 The cost . . . . . . . . . . . . . . . . . . . . . . . . . 11 10.2 The cost . . . . . . . . . . . . . . . . . . . . . . . . 11
11. Other Studies . . . . . . . . . . . . . . . . . . . . . . . . 12 11. Other Studies . . . . . . . . . . . . . . . . . . . . . . . . 12
12. Usage and Deployment Recommendations . . . . . . . . . . . . . 13 12. Usage and Deployment Recommendations . . . . . . . . . . . . 13
13. Related Proposals . . . . . . . . . . . . . . . . . . . . . . 14 13. Related Proposals . . . . . . . . . . . . . . . . . . . . . . 14
14. Security Considerations . . . . . . . . . . . . . . . . . . . 14 14. Security Considerations . . . . . . . . . . . . . . . . . . . 14
15. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 15 15. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 15
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
Normative References . . . . . . . . . . . . . . . . . . . . . . . 16 Normative References . . . . . . . . . . . . . . . . . . . . . . 16
Informative References . . . . . . . . . . . . . . . . . . . . . . 16 Informative References . . . . . . . . . . . . . . . . . . . . . 16
Appendix A - List of Concerns and Corresponding Test Results . . . 20 Appendix A - List of Concerns and Corresponding Test Results . . 20
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
This document proposes to raise the upper bound on TCP's initial This document proposes to raise the upper bound on TCP's initial
window (IW) to 10 segments (maximum 14600B). It is patterned after window (IW) to 10 segments (maximum 14600B). It is patterned after
and borrows heavily from RFC 3390 [RFC3390] and earlier work in this and borrows heavily from RFC 3390 [RFC3390] and earlier work in this
area. Due to lingering concerns about possible side effects to other area. Due to lingering concerns about possible side effects to other
flows sharing the same network bottleneck, some of the flows sharing the same network bottleneck, some of the
recommendations are conditional on additional monitoring and recommendations are conditional on additional monitoring and
evaluation. evaluation.
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allowed by RFC 3390 if there is evidence of performance issues. allowed by RFC 3390 if there is evidence of performance issues.
Further experiments are needed on the design of such a cache and Further experiments are needed on the design of such a cache and
corresponding heuristics. corresponding heuristics.
Other relevant metrics that may indicate a need to reduce the IW Other relevant metrics that may indicate a need to reduce the IW
include an increased overall percentage of packet loss or segment include an increased overall percentage of packet loss or segment
retransmissions as well as application-level metrics such as reduced retransmissions as well as application-level metrics such as reduced
data transfer completion times or impaired media quality. data transfer completion times or impaired media quality.
It is important also to take into account hosts that do not implement It is important also to take into account hosts that do not implement
a larger initial window. Furthermore, non-TCP traffic (such as VoIP) a larger initial window. Furthermore, any deployment of IW10 should
should be monitored as well. If users observe any significant be aware that there are potential side effects to real-time traffic
deterioration of performance, they SHOULD fall back to an initial (such as VoIP). If users observe any significant deterioration of
window as allowed by RFC 3390 for safety reasons. An increased performance, they SHOULD fall back to an initial window as allowed by
initial window MUST NOT be turned on by default on systems without RFC 3390 for safety reasons. An increased initial window MUST NOT be
such monitoring capabilities. turned on by default on systems without such monitoring capabilities.
The IETF TCPM working group is very much interested in further The IETF TCPM working group is very much interested in further
reports from experiments with this specification and encourages the reports from experiments with this specification and encourages the
publication of such measurement data. If no significant harm is publication of such measurement data. By now, there are no adequate
reported, a follow-up document may revisit the question on whether a studies available that either prove or or do not prove impact of IW10
larger initial window can be safely used by default in all Internet to real-time traffic. Further experimentation in this directions in
hosts. Resolution of these experiments and tighter specifications of encouraged.
the suggestions here might be grounds for a future standards track
document on the same topic. If no significant harm is reported, a follow-up document may revisit
the question on whether a larger initial window can be safely used by
default in all Internet hosts. Resolution of these experiments and
tighter specifications of the suggestions here might be grounds for a
future standards track document on the same topic.
13. Related Proposals 13. Related Proposals
Two other proposals [All10, Tou12] have been published to raise TCP's Two other proposals [All10, Tou12] have been published to raise TCP's
initial window size over a large timescale. Both aim at reducing the initial window size over a large timescale. Both aim at reducing the
uncertain impact of a larger initial window at an Internet wide uncertain impact of a larger initial window at an Internet wide
scale. Moreover, [Tou12] seeks an algorithm to automate the scale. Moreover, [Tou12] seeks an algorithm to automate the
adjustment of IW safely over long haul period. adjustment of IW safely over long haul period.
Although a modest, static increase of IW to 10 may address the near- Although a modest, static increase of IW to 10 may address the near-
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