draft-ietf-tcpm-alternativebackoff-ecn-08.txt   draft-ietf-tcpm-alternativebackoff-ecn-09.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: February 8, 2019 G. Armitage Expires: February 15, 2019 G. Armitage
Netflix Netflix
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
August 7, 2018 August 14, 2018
TCP Alternative Backoff with ECN (ABE) TCP Alternative Backoff with ECN (ABE)
draft-ietf-tcpm-alternativebackoff-ecn-08 draft-ietf-tcpm-alternativebackoff-ecn-09
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 February 8, 2019. This Internet-Draft will expire on February 15, 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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The TCP sender response is currently specified in section 6.1.2 of The TCP sender response is currently specified in section 6.1.2 of
the ECN specification [RFC3168], updated by [RFC8311]: the ECN specification [RFC3168], updated by [RFC8311]:
The indication of congestion should be treated just as a The indication of congestion should be treated just as a
congestion loss in non-ECN-Capable TCP. That is, the TCP source congestion loss in non-ECN-Capable TCP. That is, the TCP source
halves the congestion window "cwnd" and reduces the slow start halves the congestion window "cwnd" and reduces the slow start
threshold "ssthresh", unless otherwise specified by an threshold "ssthresh", unless otherwise specified by an
Experimental RFC in the IETF document stream. Experimental RFC in the IETF document stream.
This is replaced with: Following publication of RFC8311, this document specifies a sender-
side change to TCP:
Receipt of a packet with the ECN-Echo flag SHOULD trigger the TCP 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 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. FlightSize, with a lower bound of 2 * SMSS applied to the result.
As in [RFC5681], the TCP sender also reduces the cwnd value to no As in [RFC5681], the TCP sender also reduces the cwnd value to no
more than the new ssthresh value. RFC 3168 section 6.1.2 provides more than the new ssthresh value. RFC 3168 section 6.1.2 provides
guidance on setting a cwnd less than 2 * SMSS. guidance on setting a cwnd less than 2 * SMSS.
3.1. Choice of ABE Multiplier 3.1. Choice of ABE Multiplier
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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
-09. Chnaged to "Following publication of RFC8311, this document
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.
o Updated Reference citations. o Updated Reference citations.
o Removed paragraph containing a wrong statement related to timeout o Removed paragraph containing a wrong statement related to timeout
in section 4.1. in section 4.1.
 End of changes. 6 change blocks. 
5 lines changed or deleted 9 lines changed or added

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