draft-ietf-tcpm-initcwnd-05.txt   draft-ietf-tcpm-initcwnd-06.txt 
Internet Draft J. Chu Internet Draft J. Chu
draft-ietf-tcpm-initcwnd-05.txt N. Dukkipati draft-ietf-tcpm-initcwnd-06.txt N. Dukkipati
Intended status: Experimental Y. Cheng Intended status: Experimental Y. Cheng
Updates: 3390, 5681 M. Mathis Updates: 3390, 5681 M. Mathis
Expiration date: April 2013 Google, Inc. Expiration date: May 2013 Google, Inc.
October 20, 2012 November 16, 2012
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 April, 2013. This Internet-Draft will expire on May, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 14 15. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 14
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 . . 21 Appendix A - List of Concerns and Corresponding Test Results . . 20
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . 24 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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Until this proposal is widely deployed, a fairness issue may exist Until this proposal is widely deployed, a fairness issue may exist
between flows adopting a larger initial window vs flows that are between flows adopting a larger initial window vs flows that are
RFC3390-compliant. Although no severe unfairness has been detected on RFC3390-compliant. Although no severe unfairness has been detected on
all the known tests so far, further study on this topic may be all the known tests so far, further study on this topic may be
warranted. warranted.
Some of the discussions from RFC 3390 are still valid for IW=10. Some of the discussions from RFC 3390 are still valid for IW=10.
Moreover, it is worth noting that although TCP NewReno increases the Moreover, it is worth noting that although TCP NewReno increases the
chance of duplicate segments when trying to recover multiple packet chance of duplicate segments when trying to recover multiple packet
losses from a large window [RFC3782], the wide support of TCP losses from a large window, the wide support of TCP Selective
Selective Acknowledgment (SACK) option [RFC2018] in all major OSes Acknowledgment (SACK) option [RFC2018] in all major OSes today should
today should keep the volume of duplicate segments in check. keep the volume of duplicate segments in check.
Recent measurements [Get11] provide evidence of extremely large Recent measurements [Get11] provide evidence of extremely large
queues (in the order of one second or more) at access networks of the queues (in the order of one second or more) at access networks of the
Internet. While a significant part of the buffer bloat is contributed Internet. While a significant part of the buffer bloat is contributed
by large downloads/uploads such as video files, emails with large by large downloads/uploads such as video files, emails with large
attachments, backups and download of movies to disk, some of the attachments, backups and download of movies to disk, some of the
problem is also caused by Web browsing of image heavy sites [Get11]. problem is also caused by Web browsing of image heavy sites [Get11].
This queuing delay is generally considered harmful for responsiveness This queuing delay is generally considered harmful for responsiveness
of latency sensitive traffic such as DNS queries, ARP, DHCP, VoIP and of latency sensitive traffic such as DNS queries, ARP, DHCP, VoIP and
Gaming. IW=10 can exacerbate this problem when doing short downloads Gaming. IW=10 can exacerbate this problem when doing short downloads
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Hurtig, "Early Retransmit for TCP and SCTP", RFC 5827, May Hurtig, "Early Retransmit for TCP and SCTP", RFC 5827, May
2010. 2010.
[RFC6298] Paxson, V., Allman, M., Chu, J. and M. Sargent, "Computing [RFC6298] Paxson, V., Allman, M., Chu, J. and M. Sargent, "Computing
TCP's Retransmission Timer", RFC 6298, June 2011. TCP's Retransmission Timer", RFC 6298, June 2011.
Informative References Informative References
[AKAM10] "The State of the Internet, 3rd Quarter 2009", Akamai [AKAM10] "The State of the Internet, 3rd Quarter 2009", Akamai
Technologies, Inc., January 2010. Technologies, Inc., January 2010.
URL=http://www.akamai.com/html/about/press/releases/2010/press_011310_1.html URL=http://www.akamai.com/html/about/press/releases/2010/
press_011310_1.html
[AERG11] Al-Fares, M., Elmeleegy, K., Reed, B. and I. Gashinsky, [AERG11] Al-Fares, M., Elmeleegy, K., Reed, B. and I. Gashinsky,
"Overclocking the Yahoo! CDN for Faster Web Page Loads", "Overclocking the Yahoo! CDN for Faster Web Page Loads",
Internet Measurement Conference, November 2011. Internet Measurement Conference, November 2011.
[All00] Allman, M., "A Web Server's View of the Transport Layer", [All00] Allman, M., "A Web Server's View of the Transport Layer",
ACM Computer Communication Review, 30(5), October 2000. ACM Computer Communication Review, 30(5), October 2000.
[All10] Allman, M., "Initial Congestion Window Specification", [All10] Allman, M., "Initial Congestion Window Specification",
Internet-draft draft-allman-tcpm-bump-initcwnd-00.txt, work Internet-draft draft-allman-tcpm-bump-initcwnd-00.txt, work
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Initial Window", RFC 2414, September 1998. Initial Window", RFC 2414, September 1998.
[RFC3042] Allman, M., Balakrishnan, H. and S. Floyd, "Enhancing TCP's [RFC3042] Allman, M., Balakrishnan, H. and S. Floyd, "Enhancing TCP's
Loss Recovery Using Limited Transmit", RFC 3042, January Loss Recovery Using Limited Transmit", RFC 3042, January
2001. 2001.
[RFC3150] Dawkins, S., Montenegro, G., Kojo, M. and V. Magret, "End- [RFC3150] Dawkins, S., Montenegro, G., Kojo, M. and V. Magret, "End-
to-end Performance Implications of Slow Links", BCP 0048, to-end Performance Implications of Slow Links", BCP 0048,
July 2001. July 2001.
[RFC3782] Floyd, S., Henderson, T., and A. Gurtov, "The NewReno
Modification to TCP's Fast Recovery Algorithm", RFC 3782,
April 2004.
[RFC4782] Floyd, S., Allman, M., Jain, A. and P. Sarolahti, "Quick- [RFC4782] Floyd, S., Allman, M., Jain, A. and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, January 2007. Start for TCP and IP", RFC 4782, January 2007.
[RFC6077] Papadimitriou, D., Welzl, M., Scharf, M. and B. Briscoe, [RFC6077] Papadimitriou, D., Welzl, M., Scharf, M. and B. Briscoe,
"Open Research Issues in Internet Congestion Control", "Open Research Issues in Internet Congestion Control",
section 3.4, RFC 6077, February 2011. section 3.4, RFC 6077, February 2011.
[RJ10] Ramachandran, S. and A. Jain, "Aggregate Statistics of Size [RJ10] Ramachandran, S. and A. Jain, "Aggregate Statistics of Size
Related Metrics of Web Pages metrics", May 2010. URL Related Metrics of Web Pages metrics", May 2010. URL
http://code.google.com/speed/articles/web-metrics.html http://code.google.com/speed/articles/web-metrics.html
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[SPDY] "SPDY: An experimental protocol for a faster web", URL [SPDY] "SPDY: An experimental protocol for a faster web", URL
http://dev.chromium.org/spdy http://dev.chromium.org/spdy
[Ste08] Sounders S., "Roundup on Parallel Connections", High [Ste08] Sounders S., "Roundup on Parallel Connections", High
Performance Web Sites blog. March 2008. URL Performance Web Sites blog. March 2008. URL
http://www.stevesouders.com/blog/2008/03/20/roundup-on- http://www.stevesouders.com/blog/2008/03/20/roundup-on-
parallel-connections parallel-connections
[Tou12] Touch, J., "Automating the Initial Window in TCP", [Tou12] Touch, J., "Automating the Initial Window in TCP",
Internet-draft draft-touch-tcpm-automatic-iw-02.txt, work Internet-draft draft-touch-tcpm-automatic-iw-03.txt, work
in progress, January 2012. in progress, July 16, 2012.
[VH97] Visweswaraiah, V. and J. Heidemann, "Improving Restart of [VH97] Visweswaraiah, V. and J. Heidemann, "Improving Restart of
Idle TCP Connections", Technical Report 97-661, University Idle TCP Connections", Technical Report 97-661, University
of Southern California, November 1997. of Southern California, November 1997.
Appendix A - List of Concerns and Corresponding Test Results Appendix A - List of Concerns and Corresponding Test Results
Concerns have been raised since this proposal was first published Concerns have been raised since this proposal was first published
based on a set of large scale experiments. To better understand the based on a set of large scale experiments. To better understand the
impact of a larger initial window in order to confirm or dismiss impact of a larger initial window in order to confirm or dismiss
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Although [Duk10] showed the large initial window reduced the Although [Duk10] showed the large initial window reduced the
average latency even for the dialup link class of only 56Kbps in average latency even for the dialup link class of only 56Kbps in
bandwidth, more studied were needed in order to understand the bandwidth, more studied were needed in order to understand the
effect of IW10 on slow links at the microscopic level. [CW10] was effect of IW10 on slow links at the microscopic level. [CW10] was
conducted for this purpose. conducted for this purpose.
Testbeds in [CW10] emulated a 300ms RTT, bottleneck link bandwidth Testbeds in [CW10] emulated a 300ms RTT, bottleneck link bandwidth
as low as 64Kbps, and route queue size as low as 40 packets. A as low as 64Kbps, and route queue size as low as 40 packets. A
large combination of test parameters were used. Almost all tests large combination of test parameters were used. Almost all tests
showed varying degree of latency improvement from IW=10, with only showed varying degree of latency improvement from IW=10, with only
a modest increase in the packet drop rate until a very high load a modest increase in the packet drop rate until a very high load
was injected. The testbed result was consistent with both the large was injected. The testbed result was consistent with both the large
scale data center experiments [CD10, DCCM10] and a separate study scale data center experiments [CD10, DCCM10] and a separate study
using NSC simulations [Sch11, Sch11-1]. using NSC simulations [Sch11, Sch11-1].
o How will the larger initial window affect flows with initial o How will the larger initial window affect flows with initial
windows 4KB or less? windows 4KB or less?
Flows with the larger initial window will likely grab more Flows with the larger initial window will likely grab more
bandwidth from a bottleneck link when competing against flows with bandwidth from a bottleneck link when competing against flows with
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