Congestion Exposure (ConEx) Concepts, Abstract Mechanism, and Requirements
RFC 7713
Internet Engineering Task Force (IETF) M. Mathis
Request for Comments: 7713 Google, Inc.
Category: Informational B. Briscoe
ISSN: 2070-1721 BT
December 2015
Congestion Exposure (ConEx) Concepts, Abstract Mechanism,
and Requirements
Abstract
This document describes an abstract mechanism by which senders inform
the network about the congestion recently encountered by packets in
the same flow. Today, network elements at any layer may signal
congestion to the receiver by dropping packets or by Explicit
Congestion Notification (ECN) markings, and the receiver passes this
information back to the sender in transport-layer feedback. The
mechanism described here enables the sender to also relay this
congestion information back into the network in-band at the IP layer,
such that the total amount of congestion from all elements on the
path is revealed to all IP elements along the path, where it could,
for example, be used to provide input to traffic management. This
mechanism is called Congestion Exposure, or ConEx. The companion
document, "Congestion Exposure (ConEx) Concepts and Use Cases"
(RFC 6789), provides the entry point to the set of ConEx
documentation.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7713.
Mathis & Briscoe Informational [Page 1]
RFC 7713 ConEx Concepts and Abstract Mechanism December 2015
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
3. Requirements for the ConEx Abstract Mechanism . . . . . . . . 7
3.1. Requirements for ConEx Signals . . . . . . . . . . . . . 7
3.2. Constraints on the Audit Function . . . . . . . . . . . . 8
3.3. Requirements for Non-abstract ConEx Specifications . . . 9
4. Encoding Congestion Exposure . . . . . . . . . . . . . . . . 12
4.1. Naive Encoding . . . . . . . . . . . . . . . . . . . . . 12
4.2. Null Encoding . . . . . . . . . . . . . . . . . . . . . . 13
4.3. ECN-Based Encoding . . . . . . . . . . . . . . . . . . . 13
4.4. Independent Bits . . . . . . . . . . . . . . . . . . . . 14
4.5. Codepoint Encoding . . . . . . . . . . . . . . . . . . . 14
4.6. Units Implied by an Encoding . . . . . . . . . . . . . . 15
5. Congestion Exposure Components . . . . . . . . . . . . . . . 16
5.1. Network Devices (Not Modified) . . . . . . . . . . . . . 16
5.2. Modified Senders . . . . . . . . . . . . . . . . . . . . 16
5.3. Receivers (Optionally Modified) . . . . . . . . . . . . . 17
5.4. Policy Devices . . . . . . . . . . . . . . . . . . . . . 17
5.4.1. Congestion Monitoring Devices . . . . . . . . . . . . 18
5.4.2. Rest-of-Path Congestion Monitoring . . . . . . . . . 18
5.4.3. Congestion Policers . . . . . . . . . . . . . . . . . 18
5.5. Audit . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Support for Incremental Deployment . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.1. Normative References . . . . . . . . . . . . . . . . . . 27
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