ECRIT Working Group M. Patel
Internet-Draft Nortel
Intended status: Standards Track January 22, 2009
Expires: July 26, 2009
SOS Uniform Resource Identifier (URI) Parameter for Marking of Session
Initiation Protocol (SIP) Requests related to Emergency Services
draft-patel-ecrit-sos-parameter-03.txt
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Abstract
This document defines a new Session Initiation Protocol (SIP) Uniform
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Resource Identifier (URI) parameter intended for marking SIP
registration requests related to emergency services. The usage of
this new URI parameter complements the usage of the Service Uniform
Resource Name (URN) and is not intended to replace it.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. The "sos" URI Parameter . . . . . . . . . . . . . . . . . . . . 4
4.1. REGISTER Request . . . . . . . . . . . . . . . . . . . . . 4
4.2. 2xx Reponse to REGISTER Request . . . . . . . . . . . . . . 4
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
One way to differentiate a SIP-based emergency call from an ordinary
call is by the presence of the Service URN as defined in RFC 5031
[RFC5031] (and used in the IETF emergency services architecture
described in PhoneBCP[I-D.ietf-ecrit-phonebcp]). The 3GPP IP
Multimedia Subsystem (IMS) emergency services architecture,
illustrated in 3GPP TS 23.167 [3GPP.23.167], specifies that the User
Equipment (UE) performs emergency registration prior to or during the
initiation of an emergency call. The circumstances where such an
emergency registration is required are listed below:
- the UE is not registered with its home network;
- is currently registered but roaming (to ensure that the emergency
call is handled in the visited network, as required by some
jurisdictions).
Emergency registration is possible only when the UE has sufficient
credentials to register with its home network and can detect that an
emergency session is initiated. Unfortunately, marking of the
emergency registration can not be fulfilled by the use of the Service
URN.
In some countries, it is a regulatory requirement that devices be
able to place emegency calls in circumstances where other calls may
not be permitted. When a UE issues an emergency marked REGISTER
request it informs the registrar that the contact address and the
address-of-record being registered is to be used for emergency calls,
and roaming and barring restrictions should not be applied for the
registered address-of-record. A call back from a PSAP would be
routed to the registered contact address.
This document proposes a way to mark a REGISTER message as an
emergency registration.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14, RFC 2119 [RFC2119]
3. Requirements
Req: It shall be possible to distinguish emergency registration from
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non-emergency registration by providing an appropriate indication in
the SIP header fields.
4. The "sos" URI Parameter
This section provides an overview of the proposed new URI parameter
to be used for marking REGISTER requests related to emergency
services.
A new URI parameter "sos" is defined in this document. The "sos"
parameter is appended to a URI consistent with RFC 3261 [RFC3261].
It is proposed that use of this URI parameter is restricted to the
Contact header included in the REGISTER request (and the 2xx response
to the REGISTER request) related to an emergency call only. The
"sos" URI parameter MUST NOT be considered as a replacement for the
Service URN for emergency calls originated by a UA.
4.1. REGISTER Request
When the UA sends a REGISTER request for emergency registration, the
"sos" URI parameter MUST be appended to the URI in the Contact
header. This serves as an indication to the registrar that the
request is for emergency registration.
Example:
Contact: "Alice" <sip:alice@example.com;sos> ;q=0.7; expires=3600
In the event that more than one Contact header field is included in
the REGISTER request, only the contact addresses that include the
"sos" URI parameter shall be considered as emergency registered
contact addresses.
4.2. 2xx Reponse to REGISTER Request
The "sos" URI parameter MUST be present in the Contact header in the
200 (OK) response sent by the registrar upon successful registration.
The "sos" URI parameter is appended to the URI included in the
Contact header, thus indicating to the UA that this contact address
will be included in the Contact header of an INVITE for emergency
call intiation.
5. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC 2234 [RFC2234]
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uri-parameter = *(";"value)
value = sos
6. IANA Considerations
This specification defines one new SIP URI parameter, as per the
registry created by RFC 3969 [RFC3969]
Parameter Name: sos
Predefined Values: none
Reference: [RFCXXXX]
[NOTE TO IANA: Please replace XXXX with the RFC number of this
specification.]
7. Security Considerations
As an identifier, the "sos" parameter itself does not raise any
particular security issues. The semantic described by the "sos"
parameter are meant to be well-known so privacy considerations do not
apply to the URN. The main possibility of attack involves use of the
"sos" parameter to bypass the normal procedures in order to achieve
fraudulent use of services or to bypass security procedures. The
usage of this parameter as described in this document is purely for
the purpose of the REGISTER message and hence in presence of user
authentication it is ensured that the respective user can be held
accountable.
It is RECOMMENDED to log events of misuse of the "sos" URI parameter,
for example by including it in a request or response not related to
an emergency calls.
8. Acknowledgements
The author would like to thank Keith Drage, Milo Orsic, Deb Barclay,
John-Luc Bakker, Andrew Allen, Hiroshi Ishikawa, Sean Schneyer, Peter
Leis, Georg Mayer, Marvin Bienn, Ricky Kaura, Steve Norreys, Laura
Liess, AC Mahendran, Roozbeh Atarius, Ramachandran Subramanian and
Sandeep Sharma, Brian Rosen, Hannes Tschofenig, Christer Holmberg and
Henning Schulzrinne for the discussions and contributions that lead
to this work.
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9. References
9.1. 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.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
9.2. Informative References
[I-D.ietf-ecrit-phonebcp]
Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency Calling",
draft-ietf-ecrit-phonebcp-06 (work in progress),
November 2008.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008.
[3GPP.23.167]
3GPP, "IP Multimedia Subsystem (IMS) emergency sessions",
3GPP TS 23.167 7.11.0, December 2008.
Author's Address
Milan Patel
Nortel
Maidenhead Office Park, Westacott Way
Maidenhead, Berkshire, UK
Email: milanpa@nortel.com
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