Index Journeys
RFC 8757 PROPOSED STANDARD DLEP · LATENCY

Dynamic Link Exchange Protocol (DLEP) Latency Range Extension

A DLEP extension that reports the minimum and maximum latency on a link.

On rfc-editor.org ↗
PUBLISHED
March 2020
AUTHORS
B. Cheng, L. Berger
STREAM
IETF
EXTENSION TYPE VALUE
4
DATA ITEM TYPE
28
DATA ITEM LENGTH
16 octets
LATENCY UNITS
Microseconds
DOI
10.17487/RFC8757

RFC text

Contents
Original text · RFC Editor View on rfc-editor.org ↗ 
Internet Engineering Task Force (IETF)                          B. Cheng
Request for Comments: 8757                        MIT Lincoln Laboratory
Category: Standards Track                                 L. Berger, Ed.
ISSN: 2070-1721                                  LabN Consulting, L.L.C.
                                                              March 2020


     Dynamic Link Exchange Protocol (DLEP) Latency Range Extension

Abstract

   This document defines an extension to the Dynamic Link Exchange
   Protocol (DLEP) to provide the range of latency that can be
   experienced on a link.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8757.

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
     1.1.  Key Words
   2.  Extension Usage and Identification
   3.  Latency Range Data Item
   4.  Security Considerations
   5.  IANA Considerations
     5.1.  Extension Type Value
     5.2.  Data Item Value
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175].
   It provides the exchange of link-related control information between
   DLEP peers.  DLEP peers are comprised of a modem and a router.  DLEP
   defines a base set of mechanisms as well as support for possible
   extensions.  This document defines one such extension.

   The base DLEP specification includes the Latency Data Item, which
   provides a single, implementation-dependent latency value on a link.
   This document adds the ability to relay the minimum and maximum
   latency range seen on a link.  The extension defined in this document
   is referred to as "Latency Range".

   This document defines a new DLEP Extension Type Value that is used to
   indicate the use of the extension; see Section 2.  A new DLEP Data
   Item is defined in Section 3.

1.1.  Key Words

   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.

2.  Extension Usage and Identification

   The use of the Latency Range Extension SHOULD be configurable.  To
   indicate that the Latency Range Extension is to be used, an
   implementation MUST include the Latency Range Extension Type Value in
   the Extensions Supported Data Item.  The Extensions Supported Data
   Item is sent and processed according to [RFC8175].

   Note: The usage of the extension defined in this document does not
   impact processing associated with the Latency Data Item defined in
   [RFC8175].

   The Latency Range Extension Type Value is 4; see Section 5.

3.  Latency Range Data Item

   The Latency Range Data Item serves much the same purpose as the
   Latency Data Item defined in [RFC8175] with the addition of being
   able to communicate the latency range that can be experienced by
   traffic on a link.  The Latency Range Data Item MUST be included in
   the Session Initialization Response Message, with default values to
   be used on a session-wide basis.  The Latency Range Data Item also
   MAY be carried in any message where the Latency Data Item [RFC8175]
   is allowed and is carried as an additional data item.  When present,
   the Latency Range Data Item MUST be processed according to the same
   rules as the Latency Data Item defined in [RFC8175].

   The format of the Latency Range Data Item is:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Data Item Type                | Length                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Maximum Latency                        :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   :                        Maximum Latency                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Minimum Latency                        :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   :                        Minimum Latency                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:
      28

   Length:
      16

   Maximum Latency:
      A 64-bit unsigned integer, representing the longest transmission
      delay, in microseconds, that a packet encounters as it is
      transmitted over the link.

   Minimum Latency:
      A 64-bit unsigned integer, representing the shortest transmission
      delay, in microseconds, that a packet can encounter as it is
      transmitted over the link.

4.  Security Considerations

   The extension introduces a new Data Item for DLEP.  The extension
   does not inherently introduce any additional vulnerabilities above
   those documented in [RFC8175].  The approach taken to security in
   that document applies equally when running the extension defined in
   this document.

5.  IANA Considerations

   As described below, IANA has assigned two values per this document.
   Both assignments are to registries defined by [RFC8175].

5.1.  Extension Type Value

   IANA has assigned the following value in the "Extension Type Values"
   registry within the "Dynamic Link Exchange Protocol (DLEP)
   Parameters" registry.  The new value is in the range with the
   "Specification Required" [RFC8126] policy:

                          +------+---------------+
                          | Code | Description   |
                          +======+===============+
                          | 4    | Latency Range |
                          +------+---------------+

                           Table 1: New Extension
                                 Type Value

5.2.  Data Item Value

   IANA has assigned the following value in the "Data Item Type Values"
   registry within the "Dynamic Link Exchange Protocol (DLEP)
   Parameters" registry.  The new value is in the range with the
   "Specification Required" [RFC8126] policy:

                       +-----------+---------------+
                       | Type Code | Description   |
                       +===========+===============+
                       | 28        | Latency Range |
                       +-----------+---------------+

                        Table 2: New Data Item Value

6.  References

6.1.  Normative References

   [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>.

   [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>.

   [RFC8175]  Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
              Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
              DOI 10.17487/RFC8175, June 2017,
              <https://www.rfc-editor.org/info/rfc8175>.

6.2.  Informative References

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Acknowledgments

   Helpful comments were received from members of the MANET working
   group, including Ronald in 't Velt, Henning Rogge, and Victoria
   Pritchard.

Authors' Addresses

   Bow-Nan Cheng
   MIT Lincoln Laboratory
   Massachusetts Institute of Technology
   244 Wood Street
   Lexington, MA 02421-6426
   United States of America

   Email: bcheng@ll.mit.edu


   Lou Berger (editor)
   LabN Consulting, L.L.C.

   Email: lberger@labn.net

ISO Plain Language

On this page
PROBLEMThe base DLEP latency item provides only one implementation-dependent latency value for a link.
MECHANISMThe Latency Range extension adds a data item with 64-bit maximum and minimum transmission delays, measured in microseconds.
A LATENCY RANGEDLEP peers can exchange a range of link latency alongside the existing latency item, following the same processing rules.

§1Why Add a Latency Range

DLEP exchanges link-related control information between peers, which are a modem and a router. Its base specification includes one implementation-dependent latency value for a link.

This extension adds the ability to report the minimum and maximum latency that traffic can experience on that link. It does not change processing for the existing Latency Data Item.

The base protocol gives one latency value. This extension also reports the shortest and longest transmission delays seen on the link.

§3The Latency Range Data Item

The data item has type 28 and length 16. It contains a 64-bit unsigned maximum-latency value followed by a 64-bit unsigned minimum-latency value.

Both values describe packet transmission delay over the link and are measured in microseconds. The data item must appear in the Session Initialization Response with default values for the session and may appear in other messages where the base latency item is allowed.

The data item carries two numbers in microseconds: the longest and shortest link delay. It is included during session initialization and can also accompany other permitted latency updates.

§2Enabling the Extension

The use of the Latency Range extension should be configurable. An implementation indicates that it will use the extension by including extension type value 4 in the Extensions Supported Data Item.

The RFC says that this extension does not affect processing associated with the base Latency Data Item.

DLEP peers indicate support for the extension through the existing supported-extensions data item. The base latency value continues to be handled as before.