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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 4, 2011.
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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
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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.
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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
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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
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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
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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.
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Author's Address
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
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