SIPCORE                                                  J. Winterbottom
Internet-Draft                               Winterb Consulting Services
Updates: RFC6442 (if approved)                                 R. Jesske
Intended status: Standards Track                        Deutsche Telekom
Expires: July 6, 2019 January 23, 2020                                     B. Chatras
                                                             Orange Labs
                                                               A. Hutton
                                                         January 2,
                                                           July 22, 2019

     Location Source Parameter for the SIP Geolocation Header Field


   There are some circumstances where a geolocation header field may
   contain more than one location value.  Knowing the identity of the
   node adding the location value allows the recipient more freedom in
   selecting the value to look at first rather than relying solely on
   the order of the location values.

Status of This Memo

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   This Internet-Draft will expire on July 6, 2019. January 23, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Registration of loc-src Parameter for geolocation header
           field . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   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.  The specification
   suggests that only one location value should be conveyed.  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
   location value to the SIP message from that provided by the UE.

   [RFC6442] stipulates that the order of location values 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 provide any indication of which
   node actually added the location value.  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 location values in the geolocation header field.

   This document adds a location-source (loc-src) parameter to the
   location values in [RFC6442] so that the entity adding the location
   value to geolocation header field can identify itself using its
   hostname.  How the entity adding the location value to the header
   field obtains the location information is out of scope of this

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 parameter defined in this specific is for
   use in emergency calling.  There are various architectures defined
   for providing emergency calling using SIP-based messaging.  Each has
   it 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

   This document makes no attempt to comment on these various
   architectures or the rationale for them wishing to include multiple
   location values.  It does recognize that these architectures exist
   and that there is a need to identify the entity adding the location

   The parameter defined in this specification adds the location source
   generating the location value to increase the trustworthiness of the
   location information.

   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 The loc-src
   parameter is not applicable if the administrative domain manages
   emergency calls in a way that does not require location source
   generating the location.

   The functional architecture described within ETSI [M493] is an
   example of architecture where this parameter makes sense to be used.

4.  Mechanism

   The mechanism employed adds a parameter to the location value defined
   in [RFC6442] that identifies the hostname of the entity adding the
   location value to the geolocation header field.  The Augmented BNF
   (ABNF) [RFC5234] for this parameter is shown in Figure 1.

          location-source = "loc-src=" (hostname )
          hostname = <defined in RFC3261>

                         Figure 1: Location Source

   Only a fully qualified host name is valid, an IP address MUST NOT be
   added by an entity conforming with this specification.  If a node
   conforming to this specification receives a geolocation header field
   with a loc-src parameter containing an IP address then the parameter
   MUST be removed.

   Any proxy adding a location value to a geolocation header field
   SHOULD also add its host name using the loc-src parameter so that it
   is clearly identified as the node adding the location.  A UE MUST NOT
   provide a loc-src parameter value.  If a proxy 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 location values.  The first
   location value 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 location value is an https URI the provided by a proxy
   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.

6.  Privacy Considerations

   This document doesn't change any of the privacy considerations
   described in [RFC6442].  While the addition of the loc-src parameter
   does provide an indicator of the entity that added the location in
   the signaling path this provides little more exposure than a proxy
   identity being added to the record-route header field.

7.  Security Considerations

   This document introduces the ability of a proxy or middle box to
   insert a host name indicating the that they added the specific
   location value 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 location values.  As a consequence this
   parameter should only be used by the location recipient in a trusted

   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 proxies on the path as
   well as the endpoint.  The service provider has to take care is
   scenarios when location information loc-src parameter is leaving it's own network that
   the receiving network applicable within a
   single private administrative domain or between different
   administrative domains where there is trustworthy to handle a trust relationship between
   the information
   properly. domains.  If such trustworthines trust domain 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 multiples locations and loc-src may end in
   compatibility issues.  [RFC6442] already addresses the issue of
   multiples locations.  To avoid problems of wrong interpretation of
   loc-src the value may be discarded when passed to an other domain.

8.  IANA Considerations

8.1.  Registration of loc-src Parameter for geolocation header field

   This document calls for IANA to register a new SIP header parameter
   as per the guidelines in [RFC3261], which will be added to header
   sub-registry under

   Header Field:  geolocation

   Parameter Name:  loc-src

9.  Acknowledgements

   The authors would like to thank Dale Worley for his extensive review
   of the draft The authors would like to acknowledge the constructive
   feedback provided by Paul Kyziva and Christer Holmberg.

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,

   [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,

   [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,

   [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 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
   38-40 rue du General Leclerc
   Issy Moulineaux Cedex 9  F-92794


   Andrew Hutton
   Technology Drive
   Nottingham  NG9 1LA
   Mid City Place
   London  WC1V 6EA