ECRIT Working Group C. Holmberg Internet-Draft Ericsson Intended status: Standards Track May 3, 2011 Expires: November 4, 2011 Session Initiation Protocol (SIP) Media Feature Tag to identity a Public Safety Answering Point (PSAP) Callback Call draft-holmberg-ecrit-callback-00.txt Abstract This specification defines a new Session Initiation Protocol (SIP) media feature tag, sip.psap.callback, that SIP entities can use to identity Public Safety Answering Point (PSAP) callback calls, and to associate them with a previously made emergency call. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Holmberg Expires November 4, 2011 [Page 1] Internet-Draft PSAP Callback May 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Applicability and Limitation . . . . . . . . . . . . . . . . . 3 4. User Agent Client behavior . . . . . . . . . . . . . . . . . . 3 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.2. Registration . . . . . . . . . . . . . . . . . . . . . . . 3 4.3. Emergency call . . . . . . . . . . . . . . . . . . . . . . 4 4.4. PSAP callback call . . . . . . . . . . . . . . . . . . . . 4 5. User Agent Server behavior . . . . . . . . . . . . . . . . . . 4 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Registrar behavior . . . . . . . . . . . . . . . . . . . . . . 4 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.2. Registration . . . . . . . . . . . . . . . . . . . . . . . 5 6.3. PSAP callback call . . . . . . . . . . . . . . . . . . . . 5 7. Message Flow Examples . . . . . . . . . . . . . . . . . . . . . 5 7.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 9.1. IANA Registration of the sip.psap.callback media feature tag . . . . . . . . . . . . . . . . . . . . . . . . 6 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12.1. Normative References . . . . . . . . . . . . . . . . . . . 7 12.2. Informational References . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Holmberg Expires November 4, 2011 [Page 2] Internet-Draft PSAP Callback May 2011 1. Introduction TBD 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 RFC 2119 [RFC2119]. 3. Applicability and Limitation TBD 4. User Agent Client behavior 4.1. General TBD 4.2. Registration When a UAC sends a SIP REGISTER request [RFC3261], and it wants to be able to receive explicit PSAP callback calls associated with that registration, it MUST insert a sip.psap.callback media feature tag in the Contact header field [RFC3261] of the request. The value of the sip.psap.callback MUST uniqually identity the User Agent (UA). If the UA supports the "sip.instance" media feature tag [RFC5626], it is STRONGLY RECOMMENDED that it uses the same value for the sip.psap.callback feature tag. OPEN ISSUE: Need to discuss whether the usage of a "static" value (e.g. the sip.instance value), that might also be known by other users, causes some security issues, and whether another value (that might change between emergency registrations, should be used instead. If the UAC applies the SIP Outbound mechanism [RFC5626], and establishes multiple registration flows associated with a registration, it MUST include the sip.psap.callback media feature tag in each REGISTER requests associated with every registration flow for which it wants to be able to receive explicit PSAP callback calls. The UAC MUST use the same media feature tag value for each registration flow associated with a registration. Holmberg Expires November 4, 2011 [Page 3] Internet-Draft PSAP Callback May 2011 Unless the UAC wants the registrar to remove the media feature tag associated with a registration/registration flow, the UAC MUST include the sip.psap.callback media feature tag in every SIP REGISTER request associated with the registration (or registration flow), apart from when it terminates a registration (or registration flow). 4.3. Emergency call When a UAC sends an initial SIP INVITE request [RFC3261] for an emergency call, it MUST insert a sip.psap.callback media feature tag in the Contact header field of the request. The UAC MUST use the same media feature tag value that has been used for the registration associated with the emergency call. OPEN ISSUE: Should the UAC also include the media feature tag in calls that are not identified as emergency calls by the UAC, but will be determined as emergency calls by the network? 4.4. PSAP callback call When a UAC, representing a PSAP, sends an initial SIP INVITE request for an PSAP callback call, it SHOULD insert a sip.psap.callback media feature tag in the Accept-Contact header field [RFC3841] of the request. The UAC MUST use the same media feature tag value that was used for the emergency call associated with the callback call. If the PSAP callback call comes from a Public Switched Telephony Network (PSTN), or from another interworking network, the UAC representing the PSAP will normally be located in a network interworking gateway controller, such as a in a Media Gateway Controller (MGC). If the interworking gateway controller is able to determine that the call is a PSAP callback call it MUST insert a media feature tag. If the interworking gateway controller is not aware of the media feature tag value associated with the called user, it inserts an empty media feature tag. 5. User Agent Server behavior 5.1. General TBD 6. Registrar behavior Holmberg Expires November 4, 2011 [Page 4] Internet-Draft PSAP Callback May 2011 6.1. General TBD 6.2. Registration When a registrar performs registration procedures for a user, if the associated SIP REGISTER request contains a sip.psap.callback media feature tag with a media feature tag value, the registrar MUST store the media feature tag value together with other registration data associated with the registering user. OPEN ISSUE: Is there a need for the registrar to inform the UAC that it supports, and has stored the value of, the sip.psap.callback media feature tag? 6.3. PSAP callback call When a registrar receives an initial SIP INVITE request for a call, and the Accept-Contact header field of the request contains a sip.psap.callback media feature tag, if the media feature tag value matches a value registered for the called user, and if the registrar trusts the originator of the request, the registrar can decide that the call is a PSAP callback call. If the media feature tag of the request does not contain a media feature tag value (this might be the case if the requests comes from an MGC that has been able the identity the call as a PSAP callback call, but is not aware of the media feature tag value associated with the called user), if the registrar trusts the originator of the request, and a media feature tag value has been registered for the called user, the registrar MAY decide that the call is a PSAP callback call. OPEN ISSUE: If the registrar receives a request with an empty media feature tag, and decides that the call is a PSAP callback call, should the registrar add the registered media feature tag value to the media feature tag in the request? 7. Message Flow Examples 7.1. Example TBD Add example flow Holmberg Expires November 4, 2011 [Page 5] Internet-Draft PSAP Callback May 2011 Figure 1: Example call flow 8. Security Considerations TBD 9. IANA Considerations 9.1. IANA Registration of the sip.psap.callback media feature tag This section registers a new media feature tag, sip.psap.callback, into the into the SIP media feature tag tree. The required information for this registration, as specified in section 3.4 of [RFC2506], is: RFC Number: RFC XXXX [[NOTE TO IANA: Please replace XXXX with the RFC number of this specification]] Media feature tag name: sip.psap.callback ASN.1 identifier associated with feature tag: New assignment by IANA Summary of the media feature indicated by this feature tag: This feature tag indicates a unique value for a User Agent (UA), which is used to associate PSAP callback calls with emergency calls placed by the user. Values appropriate for use with this feature tag: String (equality relationship) Examples of typical use: Associating a PSAP callback call with a previously placed emergency call. Related standards or documents: RFC 3840 Security Considerations: General security considerations for media feature tags are discussed in Section 11.1 of RFC 3840. 10. Acknowledgements The original idea of using a token based mechanism to associate PSAP callback calls with emergency calls was presented by Cullen Jennings. Thanks to Fredrik Lindholm, Jan Holm and Ivo Sedlacek for their comments and feedbacks on the initial draft. Thanks to xxx for their feedback and suggestions on the ECRIT mailing Holmberg Expires November 4, 2011 [Page 6] Internet-Draft PSAP Callback May 2011 list. 11. Change Log [RFC EDITOR NOTE: Please remove this section when publishing] Changes from draft-holmberg-ecrit-callback-xx o Indicate changes from previous version 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag Registration Procedure", BCP 31, RFC 2506, March 1999. [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. [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller Preferences for the Session Initiation Protocol (SIP)", RFC 3841, August 2004. 12.2. Informational References [RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client- Initiated Connections in the Session Initiation Protocol (SIP)", RFC 5626, October 2009. Holmberg Expires November 4, 2011 [Page 7] Internet-Draft PSAP Callback May 2011 Author's Address Christer Holmberg Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: christer.holmberg@ericsson.com Holmberg Expires November 4, 2011 [Page 8]