One document matched: draft-patel-ecrit-sos-parameter-08.txt
Differences from draft-patel-ecrit-sos-parameter-07.txt
ECRIT Working Group M. Patel
Internet-Draft InterDigital Communications
Intended status: Standards Track February 15, 2010
Expires: August 19, 2010
SOS Uniform Resource Identifier (URI) Parameter for Marking of Session
Initiation Protocol (SIP) Requests related to Emergency Services
draft-patel-ecrit-sos-parameter-08.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 services. The URI
parameter is extensible to allow future values to be defined if
required by other use cases that require specific SIP registrations
to be distinctly identified. 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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 19, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The "reg-type" URI Parameter . . . . . . . . . . . . . . . . . 4
4.1. REGISTER Request . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . . . 7
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) performs emergency registration prior to or during the
initiation of an emergency call. 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).
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.
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 informs the registrar that the contact address and the
address-of-record being registered are to be used for emergency
calls, and roaming and barring restrictions should not be applied for
the registered address-of-record.
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. For
incoming calls, for example, a PSAP call back to a previously made
emergency call, addressed to the emergency registered address-of-
record can be correctly routed to the contact address and UA from
which the original emergency call was placed. In addition, any
network based services or UA endpoint based services which may
prevent the emergency call or PSAP call back from being successful
can be disabled if it can be distinguished that the registered
contact address and address-of-record pertain to emergency calls.
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
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an emergency call.
This document proposes a way to mark a REGISTER request as an
emergency registration.
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 "reg-type" 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 "reg-type" is defined in this document. The
"reg-type" 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 "reg-type" URI parameter SHALL take a value of "sos" to indicate
that the REGISTER request pertains to emergency registration. The
"reg-type" URI parameter with value "sos" MUST NOT be considered as a
replacement for the Service URN for emergency calls originated by a
UA.
Other use cases where specific instances of SIP registration need to
be identified are also possible. One such case may be by an end-user
registering their address-of-record with the specific purpose of
making "test" calls within a network. Such cases not specific to the
use case identified in this draft for identifying emergency
registration are not dealt with in this document. However the "reg-
type" URI parameter is extensible to allow other "reg-type" values to
be defined in the future.
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4.1. REGISTER Request
In networks where the UA sends a REGISTER request for emergency
registration prior to placing an emergency call, the "reg-type" URI
parameter with value "sos" 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;reg-type=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
"reg-type" URI parameter with value "sos" shall be considered as
emergency registered contact addresses.
The "reg-type" URI parameter with value "sos" 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 "reg-
type" URI parameter with value "sos" in the Contact heade field, the
registrar MUST include the "reg-type" URI parameter with value "sos"
in the Contact header field in the 200 (OK) response sent by the
registrar upon successful registration. The "reg-type" URI parameter
with value "sos" is appended to the URI included in the Contact
header, thus indicating to the UA that it needs to include this
contact address in the Contact header of an INVITE request for
emergency call initiation.
4.3. Backwards compatibility issues
The backwards compatibility scenario considered in this document is
where a legacy registrar does not support the "reg-type" URI
parameter with value "sos". In this case, if the registrar receives
a REGISTER request that includes the "reg-type" URI parameter with
value "sos" 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
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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 "reg-type" URI parameter with value "sos" in
the Contact header field. Thus the UA is unaware that the registrar
does not support the "reg-type" URI parameter with value "sos".
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 "reg-type" URI
parameter with value "sos", 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
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 "reg-type" URI parameter is a "uri-parameter", as defined by RFC
3261[RFC3261].
uri-parameter =/ reg-type-param
reg-type-param = "reg-type=" ("sos" / genvalue)
genvalue = 1*(alphanum / "-" / "." )
6. IANA Considerations
This specification defines one new SIP URI parameter, as per the
registry created by RFC 3969 [RFC3969]
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Parameter Name: reg-type
Predefined Values: sos
Reference: [RFCXXXX]
[NOTE TO IANA: Please replace XXXX with the RFC number of this
specification.]
7. Security Considerations
As an identifier, the "reg-type" parameter itself does not raise any
particular security issues. The semantic described by the "reg-type"
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 "reg-type" 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
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 "reg-type" URI
parameter with value "sos", for example by including it in a request
or response not related to an emergency call.
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.
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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.
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-14 (work in progress),
January 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 7.12.0, December 2009.
Author's Address
Milan Patel
InterDigital Communications
Email: Milan.Patel@interdigital.com
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