SIPCORE                                                  J. Winterbottom
Internet-Draft                               Winterb Consulting Services
Updates: 6442 (if approved)                                    R. Jesske
Intended status: Standards Track                        Deutsche Telekom
Expires: July 31, August 17, 2020                                      B. Chatras
                                                             Orange Labs
                                                               A. Hutton
                                                        January 28,
                                                       February 14, 2020

     Location Source Parameter for the SIP Geolocation Header Field


   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 Geolocation
   header field can identify itself using its hostname.  This document
   updates RFC 6442.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 31, August 17, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . .   3   4
   4.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Registration of loc-src parameter for Geolocation header
           field . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 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

   [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 identity 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",
   "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 it 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, 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 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

   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 RFC3261>

                         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 then the parameter address, it MUST be
   removed. 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 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/2.0
      Via: SIP/2.0/TLS;branch=z9hG4bK74bf9
      Max-Forwards: 70
      To: Bob <>
      From: Alice <>;tag=9fxced76sl
      Geolocation: <>,
      Geolocation-Routing: yes
      Accept: application/sdp, application/pidf+xml
      CSeq: 31862 INVITE
      Contact: <>
      Content-Type: multipart/mixed; boundary=boundary1
      Content-Length: ...

           Figure 2: Example Location Request. 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. 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 trust relationship
   between the domains.  If such trust domain 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 with misinterpretation of a possible corruption of
   "loc-src" parameter, location information including the value may be removed "loc-src" parameter when using
   a untrusted relationship, it is strongly recommended to delete
   location information when passed to another domain out of the trust

8.  IANA Considerations

8.1.  Registration of loc-src parameter for Geolocation header field

   The IANA is asked to add 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

   Header Field:  Geolocation

   Parameter Name:  loc-src

   Predefined Values:  No

   Reference:  this RFC

9.  Acknowledgements

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

10.  References

10.1.  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,

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323,
              DOI 10.17487/RFC3323, November 2002,

   [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,

   [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,

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              DOI 10.17487/RFC6442, December 2011,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

10.2.  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, Februar 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,

              3rd Generation Partnership Project, "3rd Generation
              Partnership Project; Technical Specification Group
              Services and System Aspects; IP Multimedia Subsystem (IMS)
              emergency sessions", TS 23.167, V 12.1.0, March 2015.

Authors' Addresses

   James Winterbottom
   Winterb Consulting Services
   Gwynneville, NSW  2500

   Phone: +61 448 266004

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

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


   Andrew Hutton
   Mid City Place
   London  WC1V 6EA