rfc8511.txt   test8511.v2v3.txt 
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and how to provide feedback on it may be obtained at and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8511. https://www.rfc-editor.org/info/rfc8511.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Definitions
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Specification
3.1. Choice of ABE Multiplier . . . . . . . . . . . . . . . . 4 3.1. Choice of ABE Multiplier
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Discussion
4.1. Rationale for Using ECN to Vary the Degree of Backoff . . 6 4.1. Rationale for Using ECN to Vary the Degree of Backoff
4.2. An RTT-Based Response to Indicated Congestion . . . . . . 7 4.2. An RTT-Based Response to Indicated Congestion
5. ABE Deployment Requirements . . . . . . . . . . . . . . . . . 7 5. ABE Deployment Requirements
6. ABE Experiment Goals . . . . . . . . . . . . . . . . . . . . 8 6. ABE Experiment Goals
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. References
9.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.1. Normative References
9.2. Informative References . . . . . . . . . . . . . . . . . 9 9.2. Informative References
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11 Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses
1. Introduction 1. Introduction
Explicit Congestion Notification (ECN) [RFC3168] makes it possible Explicit Congestion Notification (ECN) [RFC3168] makes it possible
for an Active Queue Management (AQM) mechanism to signal the presence for an Active Queue Management (AQM) mechanism to signal the presence
of incipient congestion without necessarily incurring packet loss. of incipient congestion without necessarily incurring packet loss.
This lets the network deliver some packets to an application that This lets the network deliver some packets to an application that
would have been dropped if the application or transport did not would have been dropped if the application or transport did not
support ECN. This packet loss reduction is the most obvious benefit support ECN. This packet loss reduction is the most obvious benefit
of ECN, but it is often relatively modest. Other benefits of of ECN, but it is often relatively modest. Other benefits of
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induced reduction of the congestion window (cwnd) [RFC5681]. This induced reduction of the congestion window (cwnd) [RFC5681]. This
amount of buffering effectively doubles the amount of data that can amount of buffering effectively doubles the amount of data that can
be in flight and the maximum round-trip time (RTT) experienced by the be in flight and the maximum round-trip time (RTT) experienced by the
TCP sender. TCP sender.
Modern AQM mechanisms can use ECN to signal the early signs of Modern AQM mechanisms can use ECN to signal the early signs of
impending queue buildup long before a tail-drop queue would be forced impending queue buildup long before a tail-drop queue would be forced
to resort to dropping packets. It is therefore appropriate for the to resort to dropping packets. It is therefore appropriate for the
transport protocol congestion control algorithm to have a more transport protocol congestion control algorithm to have a more
measured response when it receives an indication with an early measured response when it receives an indication with an early
warning of congestion after the remote endpoint receives an ECN warning of congestion after the remote endpoint receives an ECN CE-
CE-marked packet. Recognizing these changes in modern AQM practices, marked packet. Recognizing these changes in modern AQM practices,
the strict requirement that ECN CE signals be treated identically to the strict requirement that ECN CE signals be treated identically to
inferred packet loss has been relaxed [RFC8311]. This document inferred packet loss has been relaxed [RFC8311]. This document
therefore defines a new sender-side-only congestion control response therefore defines a new sender-side-only congestion control response
called "ABE" (Alternative Backoff with ECN). ABE improves TCP's called "ABE" (Alternative Backoff with ECN). ABE improves TCP's
average throughput when routers use AQM-controlled buffers that allow average throughput when routers use AQM-controlled buffers that allow
only for short queues. only for short queues.
2. Definitions 2. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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utilise more frequent and detailed ECN feedback (e.g., Accurate ECN utilise more frequent and detailed ECN feedback (e.g., Accurate ECN
[ACC-ECN-FEEDBACK]), which then permit a congestion control response [ACC-ECN-FEEDBACK]), which then permit a congestion control response
that adjusts the sending rate more frequently. Data Center TCP that adjusts the sending rate more frequently. Data Center TCP
(DCTCP) [RFC8257] is an example of this approach. (DCTCP) [RFC8257] is an example of this approach.
5. ABE Deployment Requirements 5. ABE Deployment Requirements
This update is a sender-side-only change. Like other changes to This update is a sender-side-only change. Like other changes to
congestion control algorithms, it does not require any change to the congestion control algorithms, it does not require any change to the
TCP receiver or to network devices. It does not require any ABE- TCP receiver or to network devices. It does not require any ABE-
specific changes in routers or the use of Accurate ECN feedback specific changes in routers or the use of Accurate ECN feedback [ACC-
[ACC-ECN-FEEDBACK] by a receiver. ECN-FEEDBACK] by a receiver.
If the method is only deployed by some senders, and not by others, If the method is only deployed by some senders, and not by others,
the senders using it can gain some advantage, possibly at the expense the senders using it can gain some advantage, possibly at the expense
of other flows that do not use this updated method. Because this of other flows that do not use this updated method. Because this
advantage applies only to ECN-marked packets and not to packet-loss advantage applies only to ECN-marked packets and not to packet-loss
indications, an ECN-Capable bottleneck will still fall back to indications, an ECN-Capable bottleneck will still fall back to
dropping packets if a TCP sender using ABE is too aggressive. The dropping packets if a TCP sender using ABE is too aggressive. The
result is no different than if the TCP sender were using traditional result is no different than if the TCP sender were using traditional
loss-based congestion control. loss-based congestion control.
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9.2. Informative References 9.2. Informative References
[ABE-REVISION] [ABE-REVISION]
Stewart, L., "ABE patch review in FreeBSD", Stewart, L., "ABE patch review in FreeBSD",
Revision 331214, March 2018, <https://svnweb.freebsd.org/ Revision 331214, March 2018, <https://svnweb.freebsd.org/
base?view=revision&revision=331214>. base?view=revision&revision=331214>.
[ABE2017] Khademi, N., Armitage, G., Welzl, M., Zander, S., [ABE2017] Khademi, N., Armitage, G., Welzl, M., Zander, S.,
Fairhurst, G., and D. Ros, "Alternative backoff: Achieving Fairhurst, G., and D. Ros, "Alternative backoff: Achieving
low latency and high throughput with ECN and AQM", IFIP low latency and high throughput with ECN and AQM",
Networking Conference and Workshops Stockholm, Sweden, DOI 10.23919/IFIPNetworking.2017.8264863, IFIP Networking
DOI 10.23919/IFIPNetworking.2017.8264863, June 2017. Conference and Workshops Stockholm, Sweden, June 2017,
<https://doi.org/10.23919/IFIPNetworking.2017.8264863>.
[ACC-ECN-FEEDBACK] [ACC-ECN-FEEDBACK]
Briscoe, B., Kuehlewind, M., and R. Scheffenegger, "More Briscoe, B., Kuehlewind, M., and R. Scheffenegger, "More
Accurate ECN Feedback in TCP", Work in Progress, Accurate ECN Feedback in TCP", Work in Progress, draft-
draft-ietf-tcpm-accurate-ecn-07, July 2018. ietf-tcpm-accurate-ecn-07, 2 July 2018.
[BUFFERBLOAT] [BUFFERBLOAT]
Gettys, J. and K. Nichols, "Bufferbloat: Dark Buffers in Gettys, J. and K. Nichols, "Bufferbloat: Dark Buffers in
the Internet", ACM Queue, Volume 9, Issue 11, the Internet", DOI 10.1145/2063166.2071893, ACM
DOI 10.1145/2063166.2071893, November 2011, Queue, Volume 9, Issue 11, November 2011,
<https://queue.acm.org/detail.cfm?id=2071893>. <https://queue.acm.org/detail.cfm?id=2071893>.
[ICC2002] Kwon, M. and S. Fahmy, "TCP increase/decrease behavior [ICC2002] Kwon, M. and S. Fahmy, "TCP increase/decrease behavior
with explicit congestion notification (ECN)", 2002 IEEE with explicit congestion notification (ECN)",
International Conference on Communications Conference DOI 10.1109/ICC.2002.997262, Cat. No.02CH37333, ICC 2002,
Proceedings, ICC 2002, Cat. No.02CH37333, 2002 IEEE International Conference on
DOI 10.1109/ICC.2002.997262, May 2002, Communications Conference Proceedings, May 2002,
<http://dx.doi.org/10.1109/ICC.2002.997262>. <http://dx.doi.org/10.1109/ICC.2002.997262>.
[RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White, [RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White,
"Proportional Integral Controller Enhanced (PIE): A "Proportional Integral Controller Enhanced (PIE): A
Lightweight Control Scheme to Address the Bufferbloat Lightweight Control Scheme to Address the Bufferbloat
Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017, Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017,
<https://www.rfc-editor.org/info/rfc8033>. <https://www.rfc-editor.org/info/rfc8033>.
[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using [RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using
Explicit Congestion Notification (ECN)", RFC 8087, Explicit Congestion Notification (ECN)", RFC 8087,
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Finally, the authors would like to thank everyone who provided Finally, the authors would like to thank everyone who provided
feedback on the congestion control behaviour specified in this feedback on the congestion control behaviour specified in this
document that was received from the IRTF Internet Congestion Control document that was received from the IRTF Internet Congestion Control
Research Group (ICCRG). Research Group (ICCRG).
Authors' Addresses Authors' Addresses
Naeem Khademi Naeem Khademi
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo N-0316 N-0316 Oslo
Norway Norway
Email: naeemk@ifi.uio.no Email: naeemk@ifi.uio.no
Michael Welzl Michael Welzl
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
Oslo N-0316 N-0316 Oslo
Norway Norway
Email: michawe@ifi.uio.no Email: michawe@ifi.uio.no
Grenville Armitage
Netflix Inc.
Email: garmitage@netflix.com Email: garmitage@netflix.com
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
School of Engineering, Fraser Noble Building School of Engineering, Fraser Noble Building
Aberdeen AB24 3UE Aberdeen
AB24 3UE
United Kingdom United Kingdom
Email: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
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