



Internet Engineering Task Force (IETF)                   J. Winterbottom
Request for Comments: 8787                   Winterb Consulting Services
Updates: 6442                                                  R. Jesske
Category: Standards Track                               Deutsche Telekom
ISSN: 2070-1721                                               B. Chatras
                                                             Orange Labs
                                                               A. Hutton
                                                                    Atos
                                                                May 2020


     Location Source Parameter for the SIP Geolocation Header Field

Abstract

   There are some circumstances where a Geolocation header field may
   contain more than one locationValue.  Knowing the identity of the
   node adding the locationValue allows the recipient more freedom in
   selecting the value to look at first rather than relying solely on
   the order of the locationValues.  This document defines the "loc-src"
   parameter so that the entity adding the locationValue to the
   Geolocation header field can identify itself using its hostname.
   This document updates RFC 6442.

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/rfc8787.

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
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   publication of this document.  Please review these documents
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   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
   2.  Terminology
   3.  Rationale
   4.  Mechanism
   5.  Example
   6.  Privacy Considerations
   7.  Security Considerations
   8.  IANA Considerations
     8.1.  Registration of "loc-src" Parameter for Geolocation Header
           Field
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   The SIP Geolocation specification [RFC6442] describes the
   "Geolocation" SIP header field, which is used to indicate that the
   SIP message is conveying location information.  [RFC6442] specifies
   that SIP intermediaries should not add locationValues to a SIP
   request that already contains a locationValue.  [RFC6442] also states
   that if a SIP intermediary adds location, it is fully responsible for
   addressing the concerns of any 424 (Bad Location Information) SIP
   response it receives.  However, some communications architectures,
   such as 3GPP [TS23-167] and ETSI [M493], prefer to use information
   provided by edge proxies or acquired through the use of core-network
   nodes before using information provided solely by user equipment
   (UE).  These solutions don't preclude the use of UE-provided location
   but require a means of being able to distinguish the identity of the
   node adding the locationValue to the SIP message from that provided
   by the UE.

   [RFC6442] stipulates that the order of locationValues in the
   Geolocation header field is the same as the order in which they were
   added to the header field.  Whilst this order provides guidance to
   the recipient as to which values were added to the message earlier in
   the communication chain, it does not identify which node added the
   locationValue.  Knowing the identity of the entity that added the
   location to the message allows the recipient to choose which location
   to consider first rather than relying solely on the order of the
   locationValues in the Geolocation header field.

   This document extends the Geolocation header field of [RFC6442] by
   allowing an entity adding the locationValue to identify itself using
   a hostname.  This is done by defining a new geoloc-param header field
   parameter, "loc-src".  How the entity adding the locationValue to the
   header field obtains the location information is out of scope of this
   document.  Please note that the "loc-src" parameter field does not
   alter the subject of the locationValue.

2.  Terminology

   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.  Rationale

   The primary intent of the "loc-src" parameter in this specification
   is for use in emergency calling.  There are various architectures
   defined for providing emergency calling using SIP-based messaging.
   Each has its own characteristics with corresponding pros and cons.
   All of them allow the UE to provide location information; however,
   many also attach other sources of location information to support
   veracity checks, to provide backup information, or to be used as the
   primary location.

   This document does not comment on these various architectures or on
   the rationale for including multiple locationValues.  It does
   recognize that these architectures exist and that there is a need to
   identify the entity adding the location information.

   The "loc-src" parameter adds the location source generating the
   locationValue to allow recipients to make informed decisions about
   which of the multiple values to use.

   The "loc-src" parameter is applicable within a single private
   administrative domain or between different administrative domains
   where there is a trust relationship between the domains.  Thus, it is
   intended to use this parameter only in trust domains where Spec(T) as
   described in [RFC3325] exists.

   The "loc-src" parameter is not included in a SIP message sent to
   another network if there is no trust relationship.  The "loc-src"
   parameter is not applicable if the administrative domain manages
   emergency calls in a way that does not require any generation of the
   location.

   The functional architecture to support emergency caller location
   described within ETSI [M493] is an example of an architecture where
   it makes sense to use this parameter.

4.  Mechanism

   The mechanism adds a geoloc-param parameter to the locationValue
   defined in [RFC6442] that identifies the hostname of the entity
   adding the locationValue to the Geolocation header field.  The
   Augmented BNF (ABNF) [RFC5234] for this parameter is shown in
   Figure 1.

          location-source = "loc-src" EQUAL hostname
          hostname = <defined in RFC 3261>

                         Figure 1: Location Source

   Only a fully qualified host name is valid.  The syntax does not
   support IP addresses, and if an entity conforming to this
   specification receives a Geolocation header field with a "loc-src"
   parameter containing an IP address, it MUST remove the parameter.

   A SIP intermediary conformant to this specification adding a
   locationValue to a Geolocation header field SHOULD also add a "loc-
   src" header field parameter so that it is clearly identified as the
   node adding the location.  A User Agent (UA) MUST NOT insert a "loc-
   src" header field parameter.  If a SIP intermediary receives a
   message from an untrusted source with the "loc-src" parameter set,
   then it MUST remove the "loc-src" parameter before passing the
   message into a trusted network.

5.  Example

   The following example shows a SIP INVITE message containing a
   Geolocation header field with two locationValues.  The first
   locationValue points to a Presence Information Data Format Location
   Object (PIDF-LO) in the SIP body using a content-indirection (cid:)
   URI per [RFC4483], and this is provided by the UE.  The second
   locationValue is an https URI provided by a SIP intermediary, which
   identifies itself using the "loc-src" parameter.

      INVITE sip:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
      Max-Forwards: 70
      To: Bob <sip:bob@biloxi.example.com>
      From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
      Call-ID: 3848276298220188511@atlanta.example.com
      Geolocation: <cid:target123@atlanta.example.com>,
           <https://lis.example.com:8222/y77syc7cuecbh>;
                    loc-src=edgeproxy.example.com
      Geolocation-Routing: yes
      Accept: application/sdp, application/pidf+xml
      CSeq: 31862 INVITE
      Contact: <sip:alice@atlanta.example.com>
      Content-Type: multipart/mixed; boundary=boundary1
      Content-Length: ...

            Figure 2: Example Location Request (in Trust Domain)

6.  Privacy Considerations

   This document doesn't change any of the privacy considerations
   described in [RFC6442].  While the addition of the "loc-src"
   parameter identifies the entity that added the location in the
   signaling path, this addition provides little more exposure than
   adding a proxy identity to the Record-Route header field (privacy
   defined in [RFC3323]).

7.  Security Considerations

   This document introduces the ability of a SIP intermediary to insert
   a host name indicating that they added the specific locationValue to
   the Geolocation header field.  The intent is for this field to be
   used by the location recipient in the event that the SIP message
   contains multiple locationValues.  As a consequence, this parameter
   should only be used by the location recipient in a trusted network.
   Adding this parameter in an untrusted network serves solely to give
   location information to untrusted parties and is NOT RECOMMENDED.

   As already stated in [RFC6442], securing the location hop by hop,
   using TLS, protects the message from eavesdropping and modification
   in transit but exposes the information to all SIP intermediaries on
   the path as well as the endpoint.  The "loc-src" parameter is
   applicable within a single private administrative domain or between
   different administrative domains where there is a relationship
   between the domains.  If such a trust relationship is not given, it
   is strongly recommended to delete the location information.

   The use of this parameter is not restricted to a specific
   architecture, but using multiple locations and loc-src may end in
   compatibility issues.  [RFC6442] already addresses the issue of
   multiple locations.  To avoid problems of a possible corruption of
   the location information including the "loc-src" parameter when using
   an untrusted relationship, it is strongly recommended to delete
   location information when passed to another domain out of the trust
   domain.

8.  IANA Considerations

8.1.  Registration of "loc-src" Parameter for Geolocation Header Field

   IANA has added a new SIP header field parameter for the Geolocation
   header field in the "Header Field Parameters and Parameter Values"
   subregistry (created by [RFC3968]) of the "Session Initiation
   Protocol (SIP) Parameters" registry found at
   <https://www.iana.org/assignments/sip-parameters/>.

   Header Field:  Geolocation

   Parameter Name:  loc-src

   Predefined Values:  No

   Reference:  RFC 8787

9.  References

9.1.  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>.

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323,
              DOI 10.17487/RFC3323, November 2002,
              <https://www.rfc-editor.org/info/rfc3323>.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              DOI 10.17487/RFC3325, November 2002,
              <https://www.rfc-editor.org/info/rfc3325>.

   [RFC3968]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Header Field Parameter Registry for the Session
              Initiation Protocol (SIP)", BCP 98, RFC 3968,
              DOI 10.17487/RFC3968, December 2004,
              <https://www.rfc-editor.org/info/rfc3968>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              DOI 10.17487/RFC6442, December 2011,
              <https://www.rfc-editor.org/info/rfc6442>.

   [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>.

9.2.  Informative References

   [M493]     European Telecommunications Standards Institute,
              "Functional architecture to support European requirements
              on emergency caller location determination and transport",
              ES 203 178, V 1.1.1, February 2015.

   [RFC4483]  Burger, E., Ed., "A Mechanism for Content Indirection in
              Session Initiation Protocol (SIP) Messages", RFC 4483,
              DOI 10.17487/RFC4483, May 2006,
              <https://www.rfc-editor.org/info/rfc4483>.

   [TS23-167] 3rd Generation Partnership Project, "Technical
              Specification Group Services and System Aspects; IP
              Multimedia Subsystem (IMS) emergency sessions", TS 23.167,
              V12.1.0, March 2015.

Acknowledgements

   The authors would like to thank Dale Worley, Christer Holmberg, and
   Jean Mahoney for their extensive review of this document.  The
   authors would like to acknowledge the constructive feedback provided
   by Paul Kyzivat and Robert Sparks.

Authors' Addresses

   James Winterbottom
   Winterb Consulting Services
   Gwynneville NSW 2500
   Australia

   Phone: +61 448 266004
   Email: a.james.winterbottom@gmail.com


   Roland Jesske
   Deutsche Telekom
   Heinrich-Hertz Str, 3-7
   64295 Darmstadt
   Germany

   Email: r.jesske@telekom.de
   URI:   www.telekom.de


   Bruno Chatras
   Orange Labs
   44, avenue de la Republique
   F-92320 Chatillon
   France

   Email: bruno.chatras@orange.com


   Andrew Hutton
   Atos
   Mid City Place
   London
   WC1V 6EA
   United Kingdom

   Email: andrew.hutton@atos.net
