One document matched: draft-patel-ecrit-sos-parameter-11.txt
Differences from draft-patel-ecrit-sos-parameter-10.txt
ECRIT Working Group M. Patel
Internet-Draft InterDigital Communications
Intended status: Standards Track November 9, 2010
Expires: May 13, 2011
SOS Uniform Resource Identifier (URI) Parameter for Marking of Session
Initiation Protocol (SIP) Requests related to Emergency Services
draft-patel-ecrit-sos-parameter-11.txt
Abstract
This document defines a new Session Initiation Protocol (SIP) Uniform
Resource Identifier (URI) parameter intended for marking SIP
registration requests related to emergency calls and allow admission
control to ensure successful initiation of emergency calls. The
usage of this new URI parameter complements the usage of the Service
Uniform Resource Name (URN) and is not intended to replace it.
Status of this Memo
This Internet-Draft is submitted to IETF 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-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 13, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The "sos" URI Parameter . . . . . . . . . . . . . . . . . . . . 4
4.1. REGISTER Request . . . . . . . . . . . . . . . . . . . . . 4
4.2. 2xx Response to REGISTER Request . . . . . . . . . . . . . 5
4.3. Backwards compatibility issues . . . . . . . . . . . . . . 5
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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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) needs to perform emergency registration prior to or
during the initiation of an emergency call.
In some countries, it is a regulatory requirement that devices be
able to place emergency calls in circumstances where other calls may
not be permitted. When a UAC issues an emergency marked REGISTER
request it indicates to the registrar that roaming and barring
restrictions should not be applied for the registered address-of-
record in order to successfully initiate an emergency session.
Furthermore, distinguishing emergency registration from non-emergency
registration allows the registrar to ensure that the contact address
associated with previous registration of the address-of-record
included in the emergency REGISTER request is not replaced.
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 cannot be fulfilled by the use of the Service
URN. The circumstances where such an emergency registration is
beneficial are listed below:
- the UE is not registered with its home network;
- the UE is currently registered but roaming (to ensure that the
emergency call is handled in the visited network, as required by some
jurisdictions).
This document concentrates on a use case defined by 3GPP as described
above. However, the solution proposed does not preclude other
systems that require emergency registration to occur prior to placing
an emergency call, to ensure that any subscription related
restrictions are removed to allow successful initiation of emergency
calls.
This document proposes a way to mark a REGISTER request as an
emergency registration.
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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. Requirements
Req: Where emergency registration is required prior to placing an
emergency call, it shall be possible to distinguish emergency
registration from non-emergency registration.
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.
Inclusion of the "sos" URI parameter in a REGISTER request SHALL
indicate that the REGISTER request pertains to emergency
registration. 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
In networks where the UA sends a REGISTER request for emergency
registration prior to placing an emergency call, 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 thus requesting the registrar to not apply any
restrictions to the user's service which might prevent emergency
calls from successfully being initiated.
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
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"sos" URI parameter shall be considered as emergency registered
contact addresses.
The "sos" URI parameter MUST NOT be included in non-REGISTER
requests, and MUST NOT be included in REGISTER requests that do not
pertain to emergency calls.
4.2. 2xx Response to REGISTER Request
If the registrar receives a REGISTER request that includes the "sos"
URI parameter in the Contact header field, the registrar MUST include
the "sos" URI parameter in the Contact header field 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.
4.3. Backwards compatibility issues
The backwards compatibility scenario considered in this document is
where a legacy registrar does not support the "sos" URI parameter.
In this case, if the registrar receives a REGISTER request that
includes the "sos" URI parameter in the Contact header field, the
registrar proceeds with registration procedures and silently ignores
the URI-parameter in accordance with RFC 3261[RFC3261]. This ensures
the user is registered and thus can successfully initiate an
emergency call.
The drawback of proceeding with registration is if the address-of-
record is for example barred or has roaming restrictions applied,
then these restrictions will not be lifted and thus registration will
be unsuccessful. This can limit the UAC's ability to successfully
place an emergency call.
If registration is successful, the 200 (OK) response from a legacy
registrar includes the "sos" URI parameter in the Contact header
field. Thus the UA is unaware that the registrar does not support
the "sos" URI parameter. Providing the registration was successful,
the UA's ability to place an emergency call is not compromised. The
UA need not know that the registrar does not support the URI
parameter.
The consequence of the registrar not supporting the "sos" URI
parameter, in addition to the drawback pertaining to restrictions
applied to the address-of-record, are as follows:
- the risk of the registrar overwriting previous registrations of the
registered address-of-record, and thus disrupting any on-going non-
emergency sessions associated with the UA, its address-of-record and
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previously registered contact address.
- incoming calls, such as a PSAP call back (to a previously made
emergency call) to the registered address-of-record might not be
routed correctly to the UA that placed the emergency call, due to not
suppressing any network based services such as call forwarding, or UA
based services which can divert the call elsewhere, or if the
address-of-record is associated to more than one contact address.
5. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC 5234 [RFC5234].
The "sos" URI parameter is a "uri-parameter", as defined by RFC
3261[RFC3261].
uri-parameter =/ sos-param
sos-param = "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 semantics described by the "sos"
parameter are meant to be well-known so privacy considerations do not
apply to the URI parameter. 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 request and hence
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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 call.
Emergency registration can result in removing restrictions for
roaming and/or barring of services. Misuse of the emergency
registered AoR and contact address can be identified within the
network and thus requests for unauthorized service will be rejected.
Thus, no security considerations related to hijacking of services are
foreseen as a result of applying a marking of emergency registrations
through the use of a SIP URI parameter.
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 led to
this work.
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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[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.
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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-16 (work in progress),
October 2010.
[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 10.1.0, September 2010.
Author's Address
Milan Patel
InterDigital Communications
Email: Milan.Patel@interdigital.com
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