More Accurate ECN Feedback in TCP
draft-ietf-tcpm-accurate-ecn-01
TCP Maintenance & Minor Extensions (tcpm) B. Briscoe
Internet-Draft Simula Research Laboratory
Intended status: Experimental M. Kuehlewind
Expires: January 1, 2017 ETH Zurich
R. Scheffenegger
NetApp, Inc.
June 30, 2016
More Accurate ECN Feedback in TCP
draft-ietf-tcpm-accurate-ecn-01
Abstract
Explicit Congestion Notification (ECN) is a mechanism where network
nodes can mark IP packets instead of dropping them to indicate
incipient congestion to the end-points. Receivers with an ECN-
capable transport protocol feed back this information to the sender.
ECN is specified for TCP in such a way that only one feedback signal
can be transmitted per Round-Trip Time (RTT). Recently, new TCP
mechanisms like Congestion Exposure (ConEx) or Data Center TCP
(DCTCP) need more accurate ECN feedback information whenever more
than one marking is received in one RTT. This document specifies an
experimental scheme to provide more than one feedback signal per RTT
in the TCP header. Given TCP header space is scarce, it overloads
the three existing ECN-related flags in the TCP header and provides
additional information in a new TCP option.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 1, 2017.
Briscoe, et al. Expires January 1, 2017 [Page 1]
Internet-Draft Accurate TCP-ECN Feedback June 2016
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Roadmap . . . . . . . . . . . . . . . . . . . . 4
1.2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Experiment Goals . . . . . . . . . . . . . . . . . . . . 5
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.5. Recap of Existing ECN feedback in IP/TCP . . . . . . . . 6
2. AccECN Protocol Overview and Rationale . . . . . . . . . . . 7
2.1. Capability Negotiation . . . . . . . . . . . . . . . . . 8
2.2. Feedback Mechanism . . . . . . . . . . . . . . . . . . . 8
2.3. Delayed ACKs and Resilience Against ACK Loss . . . . . . 9
2.4. Feedback Metrics . . . . . . . . . . . . . . . . . . . . 10
2.5. Generic (Dumb) Reflector . . . . . . . . . . . . . . . . 10
3. AccECN Protocol Specification . . . . . . . . . . . . . . . . 11
3.1. Negotiation during the TCP handshake . . . . . . . . . . 11
3.2. AccECN Feedback . . . . . . . . . . . . . . . . . . . . . 14
3.2.1. The ACE Field . . . . . . . . . . . . . . . . . . . . 14
3.2.2. Safety against Ambiguity of the ACE Field . . . . . . 16
3.2.3. The AccECN Option . . . . . . . . . . . . . . . . . . 16
3.2.4. Path Traversal of the AccECN Option . . . . . . . . . 17
3.2.5. Usage of the AccECN TCP Option . . . . . . . . . . . 19
3.3. AccECN Compliance by TCP Proxies, Offload Engines and
other Middleboxes . . . . . . . . . . . . . . . . . . . . 20
4. Interaction with Other TCP Variants . . . . . . . . . . . . . 21
4.1. Compatibility with SYN Cookies . . . . . . . . . . . . . 21
4.2. Compatibility with Other TCP Options and Experiments . . 21
4.3. Compatibility with Feedback Integrity Mechanisms . . . . 21
5. Protocol Properties . . . . . . . . . . . . . . . . . . . . . 23
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