More Accurate ECN Feedback in TCP
draft-ietf-tcpm-accurate-ecn-10
TCP Maintenance & Minor Extensions (tcpm) B. Briscoe
Internet-Draft Independent
Intended status: Experimental M. Kuehlewind
Expires: September 6, 2020 Ericsson
R. Scheffenegger
NetApp
March 5, 2020
More Accurate ECN Feedback in TCP
draft-ietf-tcpm-accurate-ecn-10
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). Recent new TCP
mechanisms like Congestion Exposure (ConEx), Data Center TCP (DCTCP)
or Low Latency Low Loss Scalable Throughput (L4S) 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 allocates a reserved header bit,
that was previously used for the ECN-Nonce which has now been
declared historic. It also overloads the two existing ECN flags in
the TCP header. The resulting extra space is exploited to feed back
the IP-ECN field received during the 3-way handshake as well.
Supplementary feedback information can optionally be provided in a
new TCP option, which is never used on the TCP SYN.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Briscoe, et al. Expires September 6, 2020 [Page 1]
Internet-Draft Accurate TCP-ECN Feedback March 2020
This Internet-Draft will expire on September 6, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Roadmap . . . . . . . . . . . . . . . . . . . . 4
1.2. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Experiment Goals . . . . . . . . . . . . . . . . . . . . 5
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
1.5. Recap of Existing ECN feedback in IP/TCP . . . . . . . . 7
2. AccECN Protocol Overview and Rationale . . . . . . . . . . . 8
2.1. Capability Negotiation . . . . . . . . . . . . . . . . . 9
2.2. Feedback Mechanism . . . . . . . . . . . . . . . . . . . 9
2.3. Delayed ACKs and Resilience Against ACK Loss . . . . . . 10
2.4. Feedback Metrics . . . . . . . . . . . . . . . . . . . . 11
2.5. Generic (Dumb) Reflector . . . . . . . . . . . . . . . . 11
3. AccECN Protocol Specification . . . . . . . . . . . . . . . . 12
3.1. Negotiating to use AccECN . . . . . . . . . . . . . . . . 12
3.1.1. Negotiation during the TCP handshake . . . . . . . . 12
3.1.2. Backward Compatibility . . . . . . . . . . . . . . . 13
3.1.3. Forward Compatibility . . . . . . . . . . . . . . . . 15
3.1.4. Retransmission of the SYN . . . . . . . . . . . . . . 16
3.1.5. Implications of AccECN Mode . . . . . . . . . . . . . 17
3.2. AccECN Feedback . . . . . . . . . . . . . . . . . . . . . 18
3.2.1. Initialization of Feedback Counters . . . . . . . . . 19
3.2.2. The ACE Field . . . . . . . . . . . . . . . . . . . . 19
Show full document text