Internet Engineering Task Force (IETF)                        K. Inamdar
Request for Comments: 9409                                  Unaffiliated
Category: Informational                                     S. Narayanan
ISSN: 2070-1721                                                  D. Engi
                                                           G. Salgueiro
                                                                  Cisco
                                                              July 2023


           The 'sip-trunking-capability' Link Relation Type

Abstract

  This Informational document defines the 'sip-trunking-capability'
  link relation type that may be used by an enterprise telephony
  Session Initiation Protocol (SIP) network to retrieve a SIP trunking
  capability set document, which contains the capabilities and
  configuration requirements of an Internet Telephony Service Provider
  (ITSP).  These technical requirements allow for seamless peering
  between SIP-based enterprise telephony networks and the ITSP.

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 candidates for any level of Internet
  Standard; see 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/rfc9409.

Copyright Notice

  Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the
  Trust Legal Provisions and are provided without warranty as described
  in the Revised BSD License.

Table of Contents

  1.  Introduction
  2.  The 'sip-trunking-capability' Link Relation Type
  3.  Example Usage
  4.  IANA Considerations
  5.  Security Considerations
  6.  References
    6.1.  Normative References
    6.2.  Informative References
  Acknowledgements
  Authors' Addresses

1.  Introduction

  RFC 8288 [RFC8288] defines a way to indicate relationships between
  resources on the Web. This document specifies the 'sip-trunking-
  capability' link relation type according to the rules of RFC 8288.
  Links with this relationship type can be used to exchange capability
  information between potential peer devices.  In the event that
  systems require additional parameters and configuration to negotiate
  communication, a well-known URI can be utilized to deliver
  information to potential peers, including machine-readable
  instructions and parameters needed for peering.

  The 'sip-trunking-capability' link relation type may be used on web
  resources hosted by ITSPs to provide a structured and detailed
  capability set document.  The capability set document [SIP-AUTO-PEER]
  encapsulates a set of characteristics of an ITSP, which when
  retrieved by enterprise telephony network devices allows for
  automated establishment of SIP [RFC3261] trunking between the two
  telephony networks.

2.  The 'sip-trunking-capability' Link Relation Type

  A capability set document is hosted via web resources by the ITSP.  A
  unique location of the document can be preconfigured and provided to
  each peer by the ITSP, or a centrally published resource can be used
  that dynamically generates the capability set document based on one
  or more Uniform Resource Identifiers (URIs) [RFC3986] determined by
  the peering device.  The capability set document describes the
  configuration parameters required to successfully establish SIP
  trunking between an enterprise and an ITSP network.  The capability
  set document is composed of structured and machine-readable
  parameters that can be converted into configuration data to meet the
  communication requirements of the ITSP.  The need for an enterprise
  telephony network to obtain a capability set document from an ITSP is
  documented in "Automatic Peering for SIP Trunks" [SIP-AUTO-PEER].

3.  Example Usage

  This section provides an example of possible use of the 'sip-
  trunking-capability' relation type.  The enterprise network device
  solicits the location of the capability set document from the well-
  known URI hosted by the ITSP using the WebFinger protocol [RFC7033].
  The following examples include line breaks and indentation for
  clarity.

     GET /.well-known/webfinger?
        resource=acct%3Atrunkent1456%40example.com&
        rel=sip-trunking-capability
        HTTP/1.1
     Host: ssp1.example.com

  The location of the capability set document is returned to the
  network device in the "href" attribute.

     HTTP/1.1 200 OK
     Access-Control-Allow-Origin: *
     Content-Type: application/jrd+json
     {
        "subject" : "acct:[email protected]",
        "links" :
        [
           {
              "rel" : "sip-trunking-capability",
              "href" : "https://capserver.ssp1.example.com/capdoc.json"
           }
        ]
     }

  The ITSP may use an authentication framework such as OAuth 2.0
  [RFC6749] to determine the identity of the enterprise telephony
  network to provide the appropriate capability set document.

4.  IANA Considerations

  IANA has registered the 'sip-trunking-capability' link relation under
  the "Link Relation Types" registry as follows:

  Relation Name:  sip-trunking-capability

  Description:  Refers to a capability set document that defines
     parameters or configuration requirements for automated peering and
     communication-channel negotiation of the Session Initiation
     Protocol (SIP).

  Reference:  RFC 9409

5.  Security Considerations

  The 'sip-trunking-capability' relation type is not known to introduce
  any new security issues not already discussed in RFC 8288 for generic
  use of web-linking mechanisms.  However, it is recommended to
  exercise caution when publishing potentially sensitive capability
  information over unencrypted or unauthenticated channels.  Additional
  security recommendations are outlined in the capability set document
  definition.  See the Security Considerations section in "Automatic
  Peering for SIP Trunks" [SIP-AUTO-PEER].

6.  References

6.1.  Normative References

  [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
             DOI 10.17487/RFC8288, October 2017,
             <https://www.rfc-editor.org/info/rfc8288>.

6.2.  Informative References

  [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
             A., Peterson, J., Sparks, R., Handley, M., and E.
             Schooler, "SIP: Session Initiation Protocol", RFC 3261,
             DOI 10.17487/RFC3261, June 2002,
             <https://www.rfc-editor.org/info/rfc3261>.

  [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
             Resource Identifier (URI): Generic Syntax", STD 66,
             RFC 3986, DOI 10.17487/RFC3986, January 2005,
             <https://www.rfc-editor.org/info/rfc3986>.

  [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
             RFC 6749, DOI 10.17487/RFC6749, October 2012,
             <https://www.rfc-editor.org/info/rfc6749>.

  [RFC7033]  Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
             "WebFinger", RFC 7033, DOI 10.17487/RFC7033, September
             2013, <https://www.rfc-editor.org/info/rfc7033>.

  [SIP-AUTO-PEER]
             Inamdar, K., Narayanan, S., and C. F. Jennings, "Automatic
             Peering for SIP Trunks", Work in Progress, Internet-Draft,
             draft-ietf-asap-sip-auto-peer-07, 13 January 2023,
             <https://datatracker.ietf.org/doc/html/draft-ietf-asap-
             sip-auto-peer-07>.

Acknowledgements

  This document resulted from the discussions in the ASAP Working
  Group, especially the detailed and thoughtful comments of Paul Jones,
  Marc Petit-Huguenin, Mark Nottingham, Cullen Jennings, Jonathan
  Rosenberg, Jon Peterson, Chris Wendt, Jean Mahoney, and Murray
  Kucherawy.  Additional thanks to Joe Clarke, Tim Bray, Christopher
  Wood, Dan Romascanu, David Dong, Éric Vyncke, Robert Wilton, and Lars
  Eggert for their reviews and feedback.

Authors' Addresses

  Kaustubh Inamdar
  Unaffiliated
  Email: [email protected]


  Sreekanth Narayanan
  Cisco
  Email: [email protected]


  Derek Engi
  Cisco
  Ann Arbor, MI
  United States of America
  Phone: +1 919 392 7966
  Email: [email protected]


  Gonzalo Salgueiro
  Cisco
  7200-12 Kit Creek Rd.
  Research Triangle Park, NC 27709
  United States of America
  Phone: +1 919 392 3266
  Email: [email protected]

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