draft-ietf-tcpm-alternativebackoff-ecn-04.txt   draft-ietf-tcpm-alternativebackoff-ecn-05.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: May 19, 2018 G. Armitage Expires: June 14, 2018 G. Armitage
Swinburne University of Technology Swinburne University of Technology
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
November 15, 2017 December 11, 2017
TCP Alternative Backoff with ECN (ABE) TCP Alternative Backoff with ECN (ABE)
draft-ietf-tcpm-alternativebackoff-ecn-04 draft-ietf-tcpm-alternativebackoff-ecn-05
Abstract Abstract
Recent Active Queue Management (AQM) mechanisms allow for burst Recent Active Queue Management (AQM) mechanisms allow for burst
tolerance while enforcing short queues to minimise the time that tolerance while enforcing short queues to minimise the time that
packets spend enqueued at a bottleneck. This can cause noticeable packets spend enqueued at a bottleneck. This can cause noticeable
performance degradation for TCP connections traversing such a performance degradation for TCP connections traversing such a
bottleneck, especially if they are only a few or their bandwidth- bottleneck, especially if there are only a few flows or their
delay-product is large. An Explicit Congestion Notification (ECN) bandwidth-delay-product is large. An Explicit Congestion
signal indicates that an AQM mechanism is used at the bottleneck, and Notification (ECN) signal indicates that an AQM mechanism is used at
therefore the bottleneck network queue is likely to be short. This the bottleneck, and therefore the bottleneck network queue is likely
document therefore proposes an update to the TCP sender-side ECN to be short. This document therefore proposes an update to RFC3168,
reaction in congestion avoidance to reduce the Congestion Window which changes the TCP sender-side ECN reaction in congestion
(cwnd) by a smaller amount than the congestion control algorithm's avoidance to reduce the Congestion Window (cwnd) by a smaller amount
reaction to inferred packet loss. than the congestion control algorithm's reaction to inferred packet
loss.
Status of This Memo Status of This Memo
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.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on May 19, 2018. This Internet-Draft will expire on June 14, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Why Use ECN to Vary the Degree of Backoff? . . . . . . . 4 4.1. Why Use ECN to Vary the Degree of Backoff? . . . . . . . 4
4.2. Focus on ECN as Defined in RFC3168 . . . . . . . . . . . 5 4.2. Focus on ECN as Defined in RFC3168 . . . . . . . . . . . 5
4.3. Choice of ABE Multiplier . . . . . . . . . . . . . . . . 5 4.3. Choice of ABE Multiplier . . . . . . . . . . . . . . . . 5
5. ABE Requirements . . . . . . . . . . . . . . . . . . . . . . 7 5. ABE Requirements . . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 8. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Revision Information . . . . . . . . . . . . . . . . . . . . 9 10. Revision Information . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10 11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 10 11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Definitions 1. 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", "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].
2. Introduction 2. 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 incurring packet loss. This lets the of incipient congestion without incurring packet loss. This lets the
network deliver some packets to an application that would have been network deliver some packets to an application that would have been
dropped if the application or transport did not support ECN. This dropped if the application or transport did not support ECN. This
packet loss reduction is the most obvious benefit of ECN, but it is packet loss reduction is the most obvious benefit of ECN, but it is
often relatively modest. There are also significant other benefits often relatively modest. Other benefits of deploying ECN have been
from deploying ECN [RFC8087], including reduced end-to-end network documented in RFC8087 [RFC8087].
latency.
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 ECN congestion signals exactly the same transport protocols to treat ECN congestion signals exactly the same
as they would treat an inferred packet loss [RFC3168]. as they would treat an inferred packet loss [RFC3168].
Research has demonstrated the benefits of reducing network delays Research has demonstrated the benefits of reducing network delays
that are caused by interaction of loss-based TCP congestion control that are caused by interaction of loss-based TCP congestion control
and excessive buffering [BUFFERBLOAT]. This has led to the creation and excessive buffering [BUFFERBLOAT]. This has led to the creation
of new AQM mechanisms like PIE [RFC8033] and CoDel of new AQM mechanisms like PIE [RFC8033] and CoDel
[CODEL2012][I-D.CoDel], which prevent bloated queues that are common [CODEL2012][I-D.CoDel], which prevent bloated queues that are common
with unmanaged and excessively large buffers deployed across the with unmanaged and excessively large buffers deployed across the
Internet [BUFFERBLOAT]. Internet [BUFFERBLOAT].
skipping to change at page 4, line 7 skipping to change at page 3, line 49
changes in modern AQM practices, more recent rules have relaxed the changes in modern AQM practices, more recent rules have relaxed the
strict requirement that ECN signals be treated identically to strict requirement that ECN signals be treated identically to
inferred packet loss [I-D.ECN-exp]. Following these newer, more inferred packet loss [I-D.ECN-exp]. Following these newer, more
flexible rules, this document defines a new sender-side-only flexible rules, this document defines a new sender-side-only
congestion control response, called "ABE" (Alternative Backoff with congestion control response, called "ABE" (Alternative Backoff with
ECN). ABE improves TCP's average throughput when routers use AQM ECN). ABE improves TCP's average throughput when routers use AQM
controlled buffers that allow for short queues only. controlled buffers that allow for short queues only.
3. Specification 3. Specification
This specification describes an update to the congestion control This specification updates the congestion control algorithm of an
algorithm of an ECN-capable TCP transport protocol. It allows a TCP ECN-Capable TCP transport protocol by changing the TCP sender
stack to update the TCP sender response when it receives feedback response to feedback from the TCP receiver that indicates reception
indicating reception of a CE-marked packet (ECN-signalled congestion of a CE-marked packet, i.e., receipt of a packet with the ECN-Echo
hereafter) per Equation 4 of [RFC5681]. It RECOMMENDS that a TCP flag (defined in [RFC3168]) set.
sender multiplies the slow start threshold (ssthresh) by 0.8 times of
the FlightSize (with its minimum value set to 2 * SMSS) and reduces It updates the following text in section 6.1.2 of the ECN
the cwnd in congestion avoidance following reception of a TCP segment specification [RFC3168] :
that sets the ECN-Echo flag (defined in [RFC3168]). While this
specification concerns TCP, other transports also support a per-RTT The indication of congestion should be treated just as a
response to ECN. The method defined in this document is also congestion loss in non-ECN-Capable TCP. That is, the TCP source
applicable for such transports. halves the congestion window "cwnd" and reduces the slow start
threshold "ssthresh".
Replacing this with:
Receipt of a packet with the ECN-Echo flag SHOULD trigger the TCP
source to set the slow start threshold (ssthresh) to 0.8 times the
FlightSize, with a lower bound of 2 * SMSS applied to the result.
As in [RFC5681], the TCP sender also reduces the cwnd value to
that new ssthresh value.
4. Discussion 4. Discussion
Much of the technical background to ABE can be found in a research Much of the technical background to ABE can be found in a research
paper [ABE2017]. This paper used a mix of experiments, theory and paper [ABE2017]. This paper used a mix of experiments, theory and
simulations with standard NewReno and CUBIC to evaluate the simulations with NewReno [RFC5681] and CUBIC [I-D.CUBIC] to evaluate
technique. The technique was shown to present "...significant the technique. The technique was shown to present "...significant
performance gains in lightly-multiplexed [few concurrent flows] performance gains in lightly-multiplexed [few concurrent flows]
scenarios, without losing the delay-reduction benefits of deploying scenarios, without losing the delay-reduction benefits of deploying
CoDel or PIE". The performance improvement is achieved when reacting CoDel or PIE". The performance improvement is achieved when reacting
to ECN-Echo in congestion avoidance by multiplying cwnd and ssthresh to ECN-Echo in congestion avoidance by multiplying cwnd and ssthresh
with a value in the range [0.7,0.85]. with a value in the range [0.7,0.85].
4.1. Why Use ECN to Vary the Degree of Backoff? 4.1. Why Use ECN to Vary the Degree of Backoff?
The classic rule-of-thumb dictates that a network path needs to The classic rule-of-thumb dictates that a network path needs to
provide a BDP of bottleneck buffering if a TCP connection wishes to provide a BDP of bottleneck buffering if a TCP connection wishes to
skipping to change at page 5, line 12 skipping to change at page 5, line 16
default delay targets, CoDel and PIE both effectively emulate a default delay targets, CoDel and PIE both effectively emulate a
bottleneck with a short queue (section II, [ABE2017]) while also bottleneck with a short queue (section II, [ABE2017]) while also
allowing short traffic bursts into the queue. This provides allowing short traffic bursts into the queue. This provides
acceptable performance for TCP connections over a path with a low acceptable performance for TCP connections over a path with a low
BDP, or in highly multiplexed scenarios (many concurrent transport BDP, or in highly multiplexed scenarios (many concurrent transport
flows). However, in a lightly-multiplexed case over a path with a flows). However, in a lightly-multiplexed case over a path with a
large BDP, conventional TCP backoff leads to gaps in packet large BDP, conventional TCP backoff leads to gaps in packet
transmission and under-utilisation of the path. transmission and under-utilisation of the path.
Instead of discarding packets, an AQM mechanism is allowed to mark Instead of discarding packets, an AQM mechanism is allowed to mark
ECN-capable packets with an ECN CE-mark. The reception of a CE-mark ECN-Capable packets with an ECN CE-mark. The reception of a CE-mark
feedback not only indicates congestion on the network path, it also feedback not only indicates congestion on the network path, it also
indicates that an AQM mechanism exists at the bottleneck along the indicates that an AQM mechanism exists at the bottleneck along the
path, and hence the CE-mark likely came from a bottleneck with a path, and hence the CE-mark likely came from a bottleneck with a
controlled short queue. Reacting differently to an ECN-signalled controlled short queue. Reacting differently to an ECN-signalled
congestion than to an inferred packet loss can then yield the benefit congestion than to an inferred packet loss can then yield the benefit
of a reduced back-off when queues are short. Using ECN can also be of a reduced back-off when queues are short. Using ECN can also be
advantageous for several other reasons [RFC8087]. advantageous for several other reasons [RFC8087].
The idea of reacting differently to inferred packet loss and The idea of reacting differently to inferred packet loss and
detection of an ECN-signalled congestion pre-dates this document. detection of an ECN-signalled congestion pre-dates this document.
For example, previous research proposed using ECN CE-marked feedback For example, previous research proposed using ECN CE-marked feedback
to modify TCP congestion control behaviour via a larger to modify TCP congestion control behaviour via a larger
multiplicative decrease factor in conjunction with a smaller additive multiplicative decrease factor in conjunction with a smaller additive
increase factor [ICC2002]. The goal of this former work was to increase factor [ICC2002]. The goal of this former work was to
operate across AQM bottlenecks using Random Early Detection (RED) operate across AQM bottlenecks using Random Early Detection (RED)
that were not necessarily configured to emulate a short queue that were not necessarily configured to emulate a short queue (The
([RFC7567] notes the current status of RED as an AQM method.) current usage of RED as an Internet AQM method is limited [RFC7567]).
4.2. Focus on ECN as Defined in RFC3168 4.2. Focus on ECN as Defined in RFC3168
Some transport protocol mechanisms rely on ECN semantics that differ Some transport protocol mechanisms rely on ECN semantics that differ
from the original ECN definition [RFC3168] -- for example, Congestion from the original ECN definition [RFC3168] -- for example, Congestion
Exposure (ConEx) [RFC7713] and Datacenter TCP (DCTCP) Exposure (ConEx) [RFC7713] and Datacenter TCP (DCTCP)
[I-D.ietf-tcpm-dctcp] need more accurate ECN information than that [I-D.ietf-tcpm-dctcp] need more accurate ECN information than that
offered by the original feedback method. Other mechanisms (e.g., offered by the original feedback method. Other mechanisms (e.g.,
[I-D.ietf-tcpm-accurate-ecn]) allow the sender to adjust the rate [I-D.ietf-tcpm-accurate-ecn]) allow the sender to adjust the rate
more frequently than once each path RTT. Use of these mechanisms is more frequently than once each path RTT. Use of these mechanisms is
skipping to change at page 6, line 13 skipping to change at page 6, line 17
enabled TCP connections, only beta_{loss} applies. enabled TCP connections, only beta_{loss} applies.
In other words, in response to inferred packet loss: In other words, in response to inferred packet loss:
ssthresh = max (FlightSize * beta_{loss}, 2 * SMSS) ssthresh = max (FlightSize * beta_{loss}, 2 * SMSS)
and in response to an indication of an ECN-signalled congestion: and in response to an indication of an ECN-signalled congestion:
ssthresh = max (FlightSize * beta_{ecn}, 2 * SMSS) ssthresh = max (FlightSize * beta_{ecn}, 2 * SMSS)
and and
cwnd = ssthresh cwnd = ssthresh
where FlightSize is the amount of outstanding data in the network, where FlightSize is the amount of outstanding data in the network,
upper-bounded by the smaller of the sender's cwnd and the receiver's upper-bounded by the smaller of the sender's cwnd and the receiver's
advertised window (rwnd) [RFC5681]. The higher the values of advertised window (rwnd) [RFC5681]. The higher the values of
beta_{loss} and beta_{ecn}, the less aggressive the response of any beta_{loss} and beta_{ecn}, the less aggressive the response of any
individual backoff event. individual backoff event.
The appropriate choice for beta_{loss} and beta_{ecn} values is a The appropriate choice for beta_{loss} and beta_{ecn} values is a
skipping to change at page 6, line 42 skipping to change at page 6, line 46
a multiplier of 0.7 since kernel version 2.6.25 released in 2008. a multiplier of 0.7 since kernel version 2.6.25 released in 2008.
ABE proposes no change to beta_{loss} used by current TCP ABE proposes no change to beta_{loss} used by current TCP
implementations. implementations.
beta_{ecn} depends on how the response of a TCP connection to shallow beta_{ecn} depends on how the response of a TCP connection to shallow
AQM marking thresholds is optimised. beta_{loss} reflects the AQM marking thresholds is optimised. beta_{loss} reflects the
preferred response of each congestion control algorithm when faced preferred response of each congestion control algorithm when faced
with exhaustion of buffers (of unknown depth) signalled by packet with exhaustion of buffers (of unknown depth) signalled by packet
loss. Consequently, for any given TCP congestion control algorithm loss. Consequently, for any given TCP congestion control algorithm
the choice of beta_{ecn} is likely to be algorithm-specific, rather the choice of beta_{ecn} is likely to be algorithm-specific, rather
than a constant multiple of the algorithm's existing beta_{loss}. than a constant multiple of the algorithm's existing beta_{loss}. The
The recommended beta_{ecn} value in this document is only applicable recommended beta_{ecn} value in this document is only applicable for
for Standard TCP congestion control. Standard TCP congestion control.
A range of tests (section IV, [ABE2017]) with NewReno and CUBIC over A range of tests (section IV, [ABE2017]) with NewReno and CUBIC over
CoDel and PIE in lightly-multiplexed scenarios have explored this CoDel and PIE in lightly-multiplexed scenarios have explored this
choice of parameter. The results of these tests indicate that CUBIC choice of parameter. The results of these tests indicate that CUBIC
connections benefit from beta_{ecn} of 0.85 (cf. beta_{loss} = 0.7), connections benefit from beta_{ecn} of 0.85 (cf. beta_{loss} = 0.7),
and NewReno connections see improvements with beta_{ecn} in the range and NewReno connections see improvements with beta_{ecn} in the range
0.7 to 0.85 (cf. beta_{loss} = 0.5). 0.7 to 0.85 (cf. beta_{loss} = 0.5).
5. ABE Requirements 5. ABE 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
[I-D.ietf-tcpm-accurate-ecn] by a receiver. [I-D.ietf-tcpm-accurate-ecn] by a receiver.
RFC 3168 states that the congestion control response to an ECN- RFC3168 states that the congestion control response to an ECN-
signalled congestion is the same as the response to a dropped packet signalled congestion is the same as the response to a dropped packet
[RFC3168]. [I-D.ECN-exp] updates this specification to allow systems [RFC3168]. [I-D.ECN-exp] updates this specification to allow systems
to provide a different behaviour when they experience ECN-signalled to provide a different behaviour when they experience ECN-signalled
congestion rather than packet loss. The present specification congestion rather than packet loss. The present specification
defines such an experiment and has thus been assigned an Experimental defines such an experiment and has thus been assigned an Experimental
status before being proposed as a Standards-Track update. status before being proposed as a Standards-Track update.
The purpose of the Internet experiment is to collect experience with The purpose of the Internet experiment is to collect experience with
deployment of ABE, and confirm the safety in deployed networks using deployment of ABE, and confirm the safety in deployed networks using
this update to TCP congestion control. this update to TCP congestion control.
When used with bottlenecks that do not support ECN-marking the When used with bottlenecks that do not support ECN-marking the
specification does not modify the transport protocol. specification does not modify the transport protocol.
To evaluate the benefit, this experiment therefore requires support To evaluate the benefit, this experiment therefore requires support
in AQM routers (except to enable an ECN-marking mechanism [RFC3168] in AQM routers for ECN-marking of packets carrying the ECN-Capable
[RFC7567]) for ECN-marking of packets carrying the ECN Capable
Transport, ECT(0), codepoint [RFC3168]. Transport, ECT(0), codepoint [RFC3168].
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 that use this method can gain some advantage, possibly at the senders that use this method can gain some advantage, possibly at
the expense of other flows that do not use this updated method. the expense of other flows that do not use this updated method.
Because this advantage applies only to ECN-marked packets and not to Because this advantage applies only to ECN-marked packets and not to
packet loss indications, in the worst-case (e.g., an ABE-compliant packet loss indications, in the worst case (e.g., an ABE-compliant
TCP sender using beta_{ecn} = 1.0) the ECN-capable bottleneck will TCP sender using beta_{ecn} = 1.0) the ECN-Capable bottleneck will
still fall back to dropping packets, and the result is no different still fall back to dropping packets, and the result is no different
than if the TCP sender was using traditional loss-based congestion than if the TCP sender was using traditional loss-based congestion
control. control.
The result of this Internet experiment will be reported by A TCP sender reacts to loss or ECN marks only once per round-trip
time. Hence, if a sender would first be notified of an ECN mark and
then learn about loss in the same round-trip, it would only react to
the first notification (ECN) but not to the second (loss). RFC3168
specified a reaction to ECN that was equal to the reaction to loss
[RFC3168].
ABE also makes one congestion-response each RTT that congestion is
signalled, and therefore there is no response to loss within the same
round-trip time, since ABE has already made a reduction of the
congestion window. ABE will however respond for each round-trip time
that congestion continues to be signaled. This consecutive reduction
can protect the network against long-standing unfairness in the case
of AQM algorithms that do not keep a small average queue length.
The result of this Internet experiment will include an investigation
of cases such as the ones listed above, and be reported by
presentation to the TCPM WG (or IESG) or an implementation report at presentation to the TCPM WG (or IESG) or an implementation report at
the end of the experiment. the end of the experiment.
6. Acknowledgements 6. Acknowledgements
Authors N. Khademi, M. Welzl and G. Fairhurst were part-funded by Authors N. Khademi, M. Welzl and G. Fairhurst were part-funded by
the European Community under its Seventh Framework Programme through the European Community under its Seventh Framework Programme through
the Reducing Internet Transport Latency (RITE) project (ICT-317700). the Reducing Internet Transport Latency (RITE) project (ICT-317700).
The views expressed are solely those of the authors. The views expressed are solely those of the authors.
The authors would like to thank Stuart Cheshire for many suggestions The authors would like to thank Stuart Cheshire for many suggestions
when revising the draft, and the following people for their when revising the draft, and the following people for their
contributions to [ABE2017]: Chamil Kulatunga, David Ros, Stein contributions to [ABE2017]: Chamil Kulatunga, David Ros, Stein
Gjessing, Sebastian Zander. Thanks also to (in alphabetical order) Gjessing, Sebastian Zander. Thanks also to (in alphabetical order)
Bob Briscoe, Markku Kojo, John Leslie, Dave Taht and the TCPM working Roland Bless, Bob Briscoe, David Black, Markku Kojo, John Leslie,
group for providing valuable feedback on this document. Lawrence Stewart, Dave Taht and the TCPM working group for providing
valuable feedback on this document.
The authors would finally like to thank everyone who provided The authors would finally like to thank everyone who provided
feedback on the congestion control behaviour specified in this update feedback on the congestion control behaviour specified in this update
received from the IRTF Internet Congestion Control Research Group received from the IRTF Internet Congestion Control Research Group
(ICCRG). (ICCRG).
7. IANA Considerations 7. IANA Considerations
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
skipping to change at page 9, line 9 skipping to change at page 9, line 26
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 [I-D.CUBIC]). Unfairness may also be a result of other (e.g., CUBIC [I-D.CUBIC]). 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.
10. Revision Information 10. Revision Information
XX RFC ED - PLEASE REMOVE THIS SECTION XXX XX RFC ED - PLEASE REMOVE THIS SECTION XXX
-04. Incorporates review comments from Larence Stewart and the -05. Refined the description of the experiment based on feedback at
IETF-100. Incorporated comments from David Black.
-04. Incorporates review comments from Lawrence Stewart and the
remaining comments from Roland Bless. References are updated. remaining comments from Roland Bless. References are updated.
-03. Several review comments from Roland Bless are addressed. -03. Several review comments from Roland Bless are addressed.
Consistent terminology and equations. Clarification on the scope of Consistent terminology and equations. Clarification on the scope of
recommended beta_{ecn} value. recommended beta_{ecn} value.
-02. Corrected the equations in Section 4.3. Updated the -02. Corrected the equations in Section 4.3. Updated the
affiliations. Lower bound for cwnd is defined. A recommendation for affiliations. Lower bound for cwnd is defined. A recommendation for
window-based transport protocols is changed to cover all transport window-based transport protocols is changed to cover all transport
protocols that implement a congestion control reduction to an ECN protocols that implement a congestion control reduction to an ECN
 End of changes. 23 change blocks. 
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