draft-ietf-tcpm-alternativebackoff-ecn-11.txt   draft-ietf-tcpm-alternativebackoff-ecn-12.txt 
Network Working Group N. Khademi Network Working Group N. Khademi
Internet-Draft M. Welzl Internet-Draft M. Welzl
Intended status: Experimental University of Oslo Intended status: Experimental University of Oslo
Expires: March 4, 2019 G. Armitage Expires: March 18, 2019 G. Armitage
Netflix Netflix
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
August 31, 2018 September 14, 2018
TCP Alternative Backoff with ECN (ABE) TCP Alternative Backoff with ECN (ABE)
draft-ietf-tcpm-alternativebackoff-ecn-11 draft-ietf-tcpm-alternativebackoff-ecn-12
Abstract Abstract
Active Queue Management (AQM) mechanisms allow for burst tolerance Active Queue Management (AQM) mechanisms allow for burst tolerance
while enforcing short queues to minimise the time that packets spend while enforcing short queues to minimise the time that packets spend
enqueued at a bottleneck. This can cause noticeable performance enqueued at a bottleneck. This can cause noticeable performance
degradation for TCP connections traversing such a bottleneck, degradation for TCP connections traversing such a bottleneck,
especially if there are only a few flows or their bandwidth-delay- especially if there are only a few flows or their bandwidth-delay-
product is large. The reception of a Congestion Experienced (CE) ECN product is large. The reception of a Congestion Experienced (CE) ECN
mark indicates that an AQM mechanism is used at the bottleneck, and mark indicates that an AQM mechanism is used at the bottleneck, and
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on March 4, 2019. This Internet-Draft will expire on March 18, 2019.
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.
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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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of ECN, but it is often relatively modest. Other benefits of of ECN, but it is often relatively modest. Other benefits of
deploying ECN have been documented in RFC8087 [RFC8087]. deploying ECN have been documented in RFC8087 [RFC8087].
The rules for ECN were originally written to be very conservative, The rules for ECN were originally written to be very conservative,
and required the congestion control algorithms of ECN-Capable and required the congestion control algorithms of ECN-Capable
transport protocols to treat indications of congestion signalled by transport protocols to treat indications of congestion signalled by
ECN exactly the same as they would treat an inferred packet loss ECN exactly the same as they would treat an inferred packet loss
[RFC3168]. Research has demonstrated the benefits of reducing [RFC3168]. Research has demonstrated the benefits of reducing
network delays that are caused by interaction of loss-based TCP network delays that are caused by interaction of loss-based TCP
congestion control and excessive buffering [BUFFERBLOAT]. This has congestion control and excessive buffering [BUFFERBLOAT]. This has
led to the creation of AQM mechanisms like PIE [RFC8033] and CoDel led to the creation of AQM mechanisms like Proportional Integral
[CODEL2012][RFC8289], which prevent bloated queues that are common Controller Enhanced (PIE) [RFC8033] and Controlling Queue Delay
with unmanaged and excessively large buffers deployed across the (CoDel) [CODEL2012][RFC8289], which prevent bloated queues that are
Internet [BUFFERBLOAT]. common with unmanaged and excessively large buffers deployed across
the Internet [BUFFERBLOAT].
The AQM mechanisms mentioned above aim to keep a sustained queue The AQM mechanisms mentioned above aim to keep a sustained queue
short while tolerating transient (short-term) packet bursts. short while tolerating transient (short-term) packet bursts.
However, currently used loss-based congestion control mechanisms are However, currently used loss-based congestion control mechanisms are
not always able to effectively utilise a bottleneck link where there not always able to effectively utilise a bottleneck link where there
are short queues. For example, a TCP sender using the Reno are short queues. For example, a TCP sender using the Reno
congestion control needs to be able to store at least an end-to-end congestion control needs to be able to store at least an end-to-end
bandwidth-delay product (BDP) worth of data at the bottleneck buffer bandwidth-delay product (BDP) worth of data at the bottleneck buffer
if it is to maintain full path utilisation in the face of loss- if it is to maintain full path utilisation in the face of loss-
induced reduction of the congestion window (cwnd) [RFC5681], which induced reduction of the congestion window (cwnd) [RFC5681]. This
effectively doubles the amount of data that can be in flight, the amount of buffering effectively doubles the amount of data that can
maximum round-trip time (RTT) experience, and the path's effective be in flight and the maximum round-trip time (RTT) experienced by the
RTT using the network path. 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 CE- warning of congestion after the remote endpoint receives an ECN 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 have 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
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mechanisms that have been in use in the Internet for many years mechanisms that have been in use in the Internet for many years
(e.g., CUBIC [RFC8312]). Unfairness may also be a result of other (e.g., CUBIC [RFC8312]). Unfairness may also be a result of other
factors, including the round trip time experienced by a flow. ABE factors, including the round trip time experienced by a flow. ABE
applies only when ECN-marked packets are received, not when packets applies only when ECN-marked packets are received, not when packets
are lost, hence use of ABE cannot lead to congestion collapse. are lost, hence use of ABE cannot lead to congestion collapse.
11. Revision Information 11. Revision Information
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
-12. Corrections from Adam Roach; Benjamin Kaduk; & Ben Campbell
-10. Incorported changes following the Gen-ART review by Russ -10. Incorported changes following the Gen-ART review by Russ
Housley. Correction to URL. Housley. Correction to URL.
-09. Changed to "Following publication of RFC 8311, this document -09. Changed to "Following publication of RFC 8311, this document
specifies a sender-side change to TCP:" specifies a sender-side change to TCP:"
-08. Addressed comments from AD review on the document structure, -08. Addressed comments from AD review on the document structure,
and relationship to existing RFCs. and relationship to existing RFCs.
-07. Addressed comments following WGLC. -07. Addressed comments following WGLC.
skipping to change at page 12, line 12 skipping to change at page 12, line 12
<https://svnweb.freebsd.org/ <https://svnweb.freebsd.org/
base?view=revision&revision=331214>. base?view=revision&revision=331214>.
[ABE2017] Khademi, N., Armitage, G., Welzl, M., Fairhurst, G., [ABE2017] Khademi, N., Armitage, G., Welzl, M., Fairhurst, G.,
Zander, S., and D. Ros, "Alternative Backoff: Achieving Zander, S., 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", IFIP
NETWORKING 2017, Stockholm, Sweden, June 2017. NETWORKING 2017, Stockholm, Sweden, June 2017.
[BUFFERBLOAT] [BUFFERBLOAT]
Gettys, J. and K. Nichols, "Bufferbloat: Dark Buffers in Gettys, J. and K. Nichols, "Bufferbloat: Dark Buffers in
the Internet", November 2011. the Internet", ACM Queue 9, 11, DOI
10.1145/2063166.2071893;
https://queue.acm.org/detail.cfm?id=2071893", November
2011.
[CODEL2012] [CODEL2012]
Nichols, K. and V. Jacobson, "Controlling Queue Delay", Nichols, K. and V. Jacobson, "Controlling Queue Delay",
July 2012, <http://queue.acm.org/detail.cfm?id=2209336>. July 2012, <http://queue.acm.org/detail.cfm?id=2209336>.
[I-D.ietf-tcpm-accurate-ecn] [I-D.ietf-tcpm-accurate-ecn]
Briscoe, B., Kuehlewind, M., and R. Scheffenegger, "More Briscoe, B., Kuehlewind, M., and R. Scheffenegger, "More
Accurate ECN Feedback in TCP", draft-ietf-tcpm-accurate- Accurate ECN Feedback in TCP", draft-ietf-tcpm-accurate-
ecn-06 (work in progress), March 2018. ecn-06 (work in progress), March 2018.
[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)", IEEE with Explicit Congestion Notification (ECN)", IEEE
ICC 2002, New York, New York, USA, May 2002, ICC 2002, New York, New York, USA, May 2002,
<http://dx.doi.org/10.1109/ICC.2002.997262>. <http://dx.doi.org/10.1109/ICC.2002.997262>.
[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
Concepts, Abstract Mechanism, and Requirements", RFC 7713,
DOI 10.17487/RFC7713, December 2015,
<https://www.rfc-editor.org/info/rfc7713>.
[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,
DOI 10.17487/RFC8087, March 2017, DOI 10.17487/RFC8087, March 2017,
<https://www.rfc-editor.org/info/rfc8087>. <https://www.rfc-editor.org/info/rfc8087>.
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