Location Source Parameter for the SIP Geolocation Header Field
draft-winterbottom-dispatch-locparam-00.txt

Abstract

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
• 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. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

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
    
       

   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>,
        <https://lis.example.com:8222/y77syc7cuecbh>;
                 loc-src=edgeproxy.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: ...