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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:trunkent1456@example.com",
"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: kaustubh.ietf@gmail.com
Sreekanth Narayanan
Cisco
Email: sreenara@cisco.com
Derek Engi
Cisco
Ann Arbor, MI
United States of America
Phone: +1 919 392 7966
Email: deengi@cisco.com
Gonzalo Salgueiro
Cisco
7200-12 Kit Creek Rd.
Research Triangle Park, NC 27709
United States of America
Phone: +1 919 392 3266
Email: gsalguei@cisco.com