



MPLS Working Group                                            J. Halpern
Internet-Draft                                                 G. Mirsky
Intended status: Standards Track                                Ericsson
Expires: 28 December 2025                                   26 June 2025


      Explicit Congestion Notification Using MPLS Network Actions
                        draft-halmir-mpls-ecn-00

Abstract

   It has been broadly demonstrated that user experience improvements
   for time-critical applications have not increased at the same pace as
   network throughput (i.e., the increased bandwidth does not result in
   a corresponding increase in the user experience).  Optimizing network
   latency rather than throughput can lead to a significantly improved
   user experience for time-critical applications.  Low Latency, Low
   Loss, and Scalable Throughput (L4S) technology, introduced in RFC
   9330, uses Explicit Congestion Notification (ECN) bits by marking
   packets suffering potential congestion in the network.  L4S operates
   as a congestion-control mechanism, using markers within the data
   packets to detect and promptly respond to congestion conditions.
   This feedback loop enables devices (e.g., endpoints such as client
   devices and server devices) to adjust data flow in real-time,
   preventing bottlenecks and ensuring smoother transmission.

   RFC 5129 describes a mechanism for supporting ECN in the
   Multiprotocol Label Switching (MPLS) data plane.  That mechanism is
   based on the codepoints that take part in the Traffic Class (TC)
   field and, thus, prevent the use of TC field for traffic
   differentiation.  This document defines how ECN can be supported in
   the MPLS data plane using the MPLS Network Actions technology.

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
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   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."




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   This Internet-Draft will expire on 28 December 2025.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in this Document . . . . . . . . . . . . . .   3
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Realization of Explicit Congestion Notification as an MPLS
           Network Action  . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  ECN Encapsulation Using In-Stack MPLS Network Actions . .   4
     3.2.  ECN Encoding Using Post-Stack MPLS Network Actions  . . .   5
   4.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  ECN as an MPLS Network Action Opcode  . . . . . . . . . .   6
     5.2.  ECN as an Post-Stack Network Action Opcode  . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informational References  . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Network throughput (also referred to as bandwidth) has increased
   exponentially over the last several decades, enabling a variety of
   new features for end users, including video streaming, online gaming,
   and mixed reality implementations, as well as more advanced
   applications such as remote teleoperation and autonomous services.
   The focus on network throughput, however, underestimates the fact
   that users are primarily interested in application responsiveness
   rather than the number of bits they can transfer per second.  As a
   result, user experience improvements for time-critical applications



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   have not necessarily increased at the same pace as network throughput
   (i.e., the increased bandwidth does not result in a corresponding
   increase in the user experience).  Optimizing network latency rather
   than throughput can lead to a significantly improved user experience
   for time-critical applications.

   Low Latency, Low Loss, and Scalable Throughput (L4S) technology,
   introduced in [RFC9330], uses Explicit Congestion Notification (ECN)
   ([RFC3168]) bits in IP or TCP by marking packets suffering potential
   congestion in the network ([RFC9331]).  L4S operates as a congestion-
   control mechanism, using ECN markers within the data packets to
   detect and promptly respond to congestion conditions.  This feedback
   loop enables devices (e.g., endpoints such as client devices and
   server devices) to adjust data flow in real-time, preventing
   bottlenecks and ensuring smoother transmission.

   [RFC5129] describes a mechanism for supporting ECN in the
   Multiprotocol Label Switching (MPLS) data plane.  That mechanism is
   based on the codepoints that take part in the Traffic Class (TC)
   field [RFC3032] and, thus, prevent the use of the TC field for
   traffic differentiation.  This document defines how ECN can be
   supported in the MPLS data plane using the MPLS Network Actions
   technology ([I-D.ietf-mpls-mna-fwk]) while preserving the existing
   MPLS traffic class capability.

2.  Conventions Used in this Document

2.1.  Acronyms

   ECN: Explicit Congestion Notification

   ISD: In-Stack Data

   L4S: Low Latency, Low Loss, and Scalable Throughput

   LER: Label Edge Router

   LSR: Label Switching Router

   MPLS: Multiprotocol Label Switching

   MNA: MPLS Network Action

   NAS: Network Action Sub-stack

   PSD: Post-Stack Data

   TC: Traffic Class



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2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Realization of Explicit Congestion Notification as an MPLS Network
    Action

   MNA, according to [I-D.ietf-mpls-mna-fwk], can support ECN by an MNA
   Sub-stack using either In-Stack Data (ISD) or Post-Stack Data (PSD)
   for ancillary data.

3.1.  ECN Encapsulation Using In-Stack MPLS Network Actions

   Figure 1 displays the encoding of ECN using ISD MNA.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Opcode ECN |           Data1           |ECN|S|U| Data2 | NAL |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Format of the ECN MNA Using ISD MNA

   Where fields are defined as follows:

   *  Opcode ECN is seven-bit field.  IANA is requested to assign (TBA1)
      value Section 5.1.

   *  Data1 is 14-bit field.  It MUST be zeroed on transmission and
      ignored on reception and processing of the Opcode ECN.

   *  ECN is two-bit field.

   *  S is the Bottom of Stack one-bit flag, as defined in [RFC3032]

   *  U is a one-bit Unknown Network Action Handling field as defined in
      [I-D.ietf-mpls-mna-hdr].

   *  Data2 is four-bit field.  It MUST be zeroed on transmission and
      ignored on reception and processing of the Opcode ECN.

   *  NAL is three-bit Network Action Length as defined in
      [I-D.ietf-mpls-mna-hdr].



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3.2.  ECN Encoding Using Post-Stack MPLS Network Actions

   Figure 2 displays the encoding of ECN using PSD MNA.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |ECN PS-MNA-OP|R|R|   PS-NAL    |ECN|       Post-Stack Data     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2: Format of the ECN MNA Using PSD MNA

   Where the enclosed elements are defined as follows:

   *  ECN PS-MNA-OP is seven-bit field.  IANA is requested to assign
      (TBA2) value (Section 5.2).

   *  R - two Reserved bits as defined in [I-D.ietf-mpls-mna-ps-hdr].

   *  PS-NAL is seven-bit field as defined in
      [I-D.ietf-mpls-mna-ps-hdr].

   *  ECN is two-bit field.

   *  Post-Stack Data is 14-bit field.  It MUST be zeroed on
      transmission and ignored on reception and processing of the ECN
      PS-MNA-OP.

4.  Theory of Operation

   If an ingress Label Edge Router (LER) that supports this
   specification is enabled to use ECN MNA receives a packet with the
   indication that the endpoints of the transport protocol are ECN-
   capable or packet has experienced congestion, it MUST copy the value
   of the ECN field in the received IP packet into the ECN field of the
   ECN MNA using ISD MNA (Figure 1) or of the ECN MNA using PSD MNA
   (Figure 2).  If a transit Label Switching Router (LSR) that supports
   this specification receives an MPLS packet with MNA ECN and
   determines that the egress interface for the received packet
   experiences congestion although its buffer is not full so that the
   packet can be transmitted (see for the detailed explanation of the
   incipient congestion [RFC3168]), the LSR MUST set the ECN field to
   the Congestion Experienced (0b11) value.  If an egress LER that
   supports this specification, receives an MPLS packet with ECN MNA, it
   MUST combine the value of the ECN field with the value in the ECN
   field of the IP header of the encapsulated packet.




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   In some scenarios, the Readable Label Depth of the constructed path
   through the MPLS domain may require the placement of more than one
   ECN MNA Network Action Sub-stacks (NASes).  If that is the case, then
   the Label Switching Router that exposes the NAS with ECN MNA MUST
   copy the value of the ECN field in that NAS into the ECN field in the
   next NAS that includes ECN MNA.

5.  IANA Considerations

5.1.  ECN as an MPLS Network Action Opcode

   IANA is requested to assign an ECN codepoint (TBA1) from its Network
   Action Opcodes registry (creation requested in
   [I-D.ietf-mpls-mna-hdr]) as specified in Table 1.

     +========+======================================+===============+
     | Opcode |             Description              | Reference     |
     +========+======================================+===============+
     | TBA1   | ECN as MPLS Network Action Indicator | This document |
     +--------+--------------------------------------+---------------+

                 Table 1: ECN as MPLS Network Action Opcode

5.2.  ECN as an Post-Stack Network Action Opcode

   IANA is requested to assign an ECN codepoint (TBA1) from its Post-
   Stack Network Action Opcodes registry (creation requested in
   [I-D.ietf-mpls-mna-ps-hdr]) as specified in Table 2.

   +========+=========================================+===============+
   | Opcode |               Description               | Reference     |
   +========+=========================================+===============+
   | TBA2   | ECN as Post-Stack Network Action Opcode | This document |
   +--------+-----------------------------------------+---------------+

                Table 2: ECN as MPLS Network Action Opcode

6.  Security Considerations

   Security considerations discussed in [RFC9197], [RFC9326], and
   [I-D.ietf-mpls-mna-fwk] apply to this document.

7.  Acknowledgments

   TBA

8.  References




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8.1.  Normative References

   [I-D.ietf-mpls-mna-fwk]
              Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS
              Network Actions (MNA) Framework", Work in Progress,
              Internet-Draft, draft-ietf-mpls-mna-fwk-15, 27 December
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              mpls-mna-fwk-15>.

   [I-D.ietf-mpls-mna-hdr]
              Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
              Kompella, "MPLS Network Action (MNA) Sub-Stack Solution",
              Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr-
              12, 3 March 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-mpls-mna-hdr-12>.

   [I-D.ietf-mpls-mna-ps-hdr]
              Rajamanickam, J., Gandhi, R., Zigler, R., Li, T., and J.
              Dong, "Post-Stack MPLS Network Action (MNA) Solution",
              Work in Progress, Internet-Draft, draft-ietf-mpls-mna-ps-
              hdr-01, 30 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
              mna-ps-hdr-01>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <https://www.rfc-editor.org/info/rfc3168>.

   [RFC5129]  Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
              Marking in MPLS", RFC 5129, DOI 10.17487/RFC5129, January
              2008, <https://www.rfc-editor.org/info/rfc5129>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.





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   [RFC9197]  Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
              Ed., "Data Fields for In Situ Operations, Administration,
              and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
              May 2022, <https://www.rfc-editor.org/info/rfc9197>.

   [RFC9326]  Song, H., Gafni, B., Brockners, F., Bhandari, S., and T.
              Mizrahi, "In Situ Operations, Administration, and
              Maintenance (IOAM) Direct Exporting", RFC 9326,
              DOI 10.17487/RFC9326, November 2022,
              <https://www.rfc-editor.org/info/rfc9326>.

8.2.  Informational References

   [RFC9330]  Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G.
              White, "Low Latency, Low Loss, and Scalable Throughput
              (L4S) Internet Service: Architecture", RFC 9330,
              DOI 10.17487/RFC9330, January 2023,
              <https://www.rfc-editor.org/info/rfc9330>.

   [RFC9331]  De Schepper, K. and B. Briscoe, Ed., "The Explicit
              Congestion Notification (ECN) Protocol for Low Latency,
              Low Loss, and Scalable Throughput (L4S)", RFC 9331,
              DOI 10.17487/RFC9331, January 2023,
              <https://www.rfc-editor.org/info/rfc9331>.

Authors' Addresses

   Joel Halpern
   Ericsson
   Email: jmh@joelhalpern.com


   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com
















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