Dispatch J. Winterbottom
Internet-Draft Winterb Consulting Services
Updates: RFC6442 (if approved) L. Liess
Intended status: Standards Track Deutsche Telekom
Expires: December 4, 2015 B. Chatras
Orange Labs
A. Hutton
June 2, 2015

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.

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Table of Contents

1. Introduction

The SIP geolocation specification [RFC6442] describes a SIP header field that 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 aligns with 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 document.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

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 location. 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 information.

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=” (host / other-loc-src)
       other-loc-src = token

Figure 1: Location Source

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 sips:bob@biloxi.example.com SIP/2.0
   Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
   Max-Forwards: 70
   To: Bob <sips:bob@biloxi.example.com>
   From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
   Call-ID: 3848276298220188511@atlanta.example.com
   Geolocation: <cid:target123@atlanta.example.com>,
   Geolocation-Routing: yes
   Accept: application/sdp, application/pidf+xml
   CSeq: 31862 INVITE
   Contact: <sips:alice@atlanta.example.com>
   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 network.

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 http://www.iana.org/assignments/sip-parameters.

Header Field:
Parameter Name:

9. Acknowledgements


10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, 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, June 2002.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC6442] Polk, J., Rosen, B. and J. Peterson, "Location Conveyance for the Session Initiation Protocol", RFC 6442, December 2011.

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 1.0.5, December 2014.
[RFC4483] Burger, E., "A Mechanism for Content Indirection in Session Initiation Protocol (SIP) Messages", RFC 4483, May 2006.
[TS23-167] 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 AU Phone: +61 448 266004 EMail: a.james.winterbottom@gmail.com
Laura Liess Deutsche Telekom Heinrich-Hertz Str, 3-7 Darmstadt, 64295 Germany EMail: l.liess@telekom.de URI: www.telekom.de
Bruno Chatras Orange Labs 38-40 rue du General Leclerc Issy Moulineaux Cedex 9, F-92794 France EMail: bruno.chatras@orange.com
Andrew Hutton Unify Technology Drive Nottingham, NG9 1LA UK EMail: andrew.hutton@unify.com