Internet DRAFT - draft-mohali-dispatch-originating-cdiv-parameter
draft-mohali-dispatch-originating-cdiv-parameter
Network Working Group M. Mohali
Internet-Draft Orange
Updates: 5502 (if approved) January 11, 2017
Intended status: Informational
Expires: July 15, 2017
A P-Served-User Header Field Parameter for Originating CDIV session case
in Session Initiation Protocol (SIP)
draft-mohali-dispatch-originating-cdiv-parameter-03
Abstract
This specification defines a new parameter of the P-Served-User
header field in the Session Initiation Protocol (SIP). This new
"orig-cdiv" parameter defines the session case used by a proxy when
handling an originating session after Call Diversion (CDIV) services
has been invoked for the served user. The P-Served-User header field
is defined in RFC5502 to convey the identity of the served user and
the session case that applies to this particular communication
session and application invocation. This document updates RFC5502 to
add the "originating after CDIV" session case and to provide more
guidance for using the P-Served-User header field in IP networks that
were missing in RFC5502.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 15, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Use Case . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Proxy behavior and parameter handling . . . . . . . . . . . . 4
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
1.1. General
The P-Served-User header field was defined in [RFC5502] to address an
issue that was found in the 3rd Generation Partnership Project (3GPP)
IMS (IP Multimedia Subsystem) between an S-CSCF (Serving Call Session
Control Function) and an AS (Application Server) on the ISC (IMS
Service Control) interface. For more information on the IMS, a
detailed description can be found in [TS.3GPP.24.229].
This header field conveys the identity of the served user, his/her
registration state and the session case that applies to this
particular communication session and application invocation.
[RFC5502] defines the originating and terminating session cases for a
registered or unregistered user. This document extends the P-Served-
User header field to include the session case for a forwarded leg
when a call diversion service (CDIV) has been invoked and if an
originating service of the diverting user has to be triggered.
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The sessioncase-param parameter of the P-Served-User header field is
extended with the "orig-cdiv" parameter for this "originating after
CDIV" session case.
The following section defines usage of the "orig-cdiv" parameter of
P-Served-User header field, Section 2 specifies the proxy behavior
for handling the new header field parameter, and Section 3 discusses
the applicability and scope of this new header field parameter.
Section 4 describes the syntax and correct the syntax of [RFC5502],
Section 5 registers the P-Served-User header field parameters with
IANA, and Section 6 discusses the security properties of the
environment where this new header field parameter is intended to be
used.
1.2. Use Case
In the 3GPP IMS (IP Multimedia Subsystem), the S-CSCF (Serving CSCF)
is a SIP proxy that serves as a registrar and handles originating and
terminating session states for users allocated to it. This means
that any call that is originated by a specific user or any call that
is terminated to that specific user will pass through the S-CSCF that
is allocated to that user.
At the moment that an S-CSCF is allocated for a specific user, the
user profile is downloaded to the S-CSCF from the HSS (Home
Subscriber Server), see [TS.3GPP.29.228].
To be able to determine which responsibilities the S-CSCF and the
Application Server have to perform and on which user's behalf, it is
necessary to know who is the current served user, what is his/her
"registration state" and on which "session case" is the session.
[RFC5502] defines all those parameters and in particular the
originating and terminating session cases.
In the case of a call diversion service, the received request is
first considered as a terminating session case and the terminating
filter criteria configured in the S-CSCF are performed. Receiving
the call initiation request, the Application Server is able to
determine the served user and the session case (here "term") from the
received P-Served-User header field content and to execute
terminating services. When the call diversion service is executed
(as a terminating service), the Application Server changes the target
(Request-URI) of the session and a new call leg is created. This new
call leg could be considered as an originating call leg from the
diverting user but this is not the case. Indeed, the originating
user remains the same and some of the diverting user's originating
services should not be triggered as if it was an originating call.
For instance, the originating user identity should not be restricted
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because the diverting user has a privacy service for his/her own
identity. The privacy of the diverting user should apply to
information related to this user (eg. in the Histroy-Info header
field). In the same manner, some specific services will need to be
specifically triggered on the outgoing leg after a call diversion.
Without a dedicated session case for originating after CDIV, there is
no possiblity for a proxy to trigger an originating service for the
diverting user or for an Application Server to execute the procedures
for this particular session case.
For this use case, this document creates a new parameter for the
originating after CDIV session case to be embedded in the P-Served-
User header field.
2. Proxy behavior and parameter handling
The "orig-cdiv" header field parameter can be used inside a trust
domain of the P-Served-User header field by proxies that are
processing call diversion services. The following section
illustrates how this header field parameter can be used in a 3GPP
network.
For a terminating call, when receiving the initial INVITE request,
the S-CSCF will determine that the session case is for a terminating
user as described in [RFC5502], then it determines the served user by
looking at the Request-URI and saves this Request-URI. After that,
the S-CSCF starts the analysis of filter criteria and triggers the
served user Application Server for the terminating services to be
executed including in the INVITE request the P-Served-User header
field with the "sescase" parameter set to "term" and the regstate to
the corresponding value.
Based on some criteria, the Application Server concludes that the
request has to be diverted to another target user or application.
The received Request-URI is then replaced with the new diverted-to
address. The Application Server stores the successive Request-URI(s)
values by adding one or two History-Info header field entry(ies)
[RFC7044] in the outgoing INVITE. In the History-Info header field,
the served user address is tagged thanks to the mp-param header field
parameter added in entry associated to the diverted-to address
created.
In the next step, the Application Server forwards the INVITE request
back to the S-CSCF. When receiving back the INVITE request, the
S-CSCF can see that the topmost Route header field contains its own
hostname but the Request-URI does not match the saved Request-URI.
In this case, the S-CSCF updates the P-Served-User header field
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content by replacing the "sescase" parameter by the "orig-cdiv"
parameter. The PServedUser-value remains unchanged.
Then the procedure continues by forwarding the INVITE request over to
an AS that hosts the originating services of the served user
(diverting user) that specifically need to be executed on the
forwarded leg after a call diversion service.
When the Application Server receives the INVITE request, it
determines that the session case is for "orig-cdiv" session case and
will perform the originating services to be executed after
retargeting for the diverting user (i.e. served user).
This document also provides the following guidance that reminds or
clarifies the P-Served-User handling that are missing in [RFC5502]:
o This header is forbidden to be repeated within a request for a
particular session at a particular time for the reason that
session cases are mutually exclusive. This document updates
[RFC5502] to clearly state that P-Served-User header field MUST
not contain different values either comma-separated or header-
separated. This documents also updates the syntax of the header
as defined in [RFC5502] to reflect this uniqueness of parameters
values.
o Whether the "regstate" parameter is removed or not by the S-CSCF
when processing the orginating after CDIV session case is out of
the scope of this document. In one hand, it can either be
considered that the S-CSCF is able to store the previous regstate
value and that the same value applies or that the "regstate" is
not relevant after a diverting service. On the other hand, the
regstate can be combined to the orig-cdiv session case to provide
different services if the served user is registered or
unregistered. These choices are implementation dependent.
3. Applicability
The use of the P-Served-User header field extensions is only
applicable inside a Trust Domain for P-Served-User. Nodes in such a
Trust Domain explicitly trust each other to convey the served user
and to be responsible for withholding that information outside of the
Trust Domain. The means by which the network determines the served
user and the policies that are executed for a specific served user is
outside the scope of this document.
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4. Syntax
4.1. General
[RFC5502] defines the P-Served-User header field with the
sessioncase-param parameter "sescase" which is specified as having
"orig" and "term" predefined values. This document defines an
additional parameter for the sessioncase-param: "orig-cdiv".
Because this document extends the existing sessioncase-param
parameter in a special way and that it has been identified errors in
the syntax of the P-Served-User header field as defined in [RFC5502],
this document corrects and extends the header at the same time.
The extension of the sessioncase-param parameter to add the "orig-
cdiv" session case is done in a way to fit the parameter format
introduced in release 11 of the 3GPP [TS.3GPP.24.229] and keep a
backward compatibility.
"EQUAL", "HCOLON", "SEMI", "name-addr", "addr-spec", and "generic-
param" are defined in [RFC3261].
4.2. ABNF
The augmented Backus-Naur Form (ABNF) [RFC5234] syntax of the P-
Served-User header field is described in [RFC5502].
This document updates [RFC5502] to correct the P-Served-User header
field ABNF syntax and extend it as following:
P-Served-User = "P-Served-User" HCOLON PServedUser-value
*(SEMI served-user-param)
served-user-param = sessioncase-param
/ registration-state-param
/ generic-param
PServedUser-value = name-addr / addr-spec
sessioncase-param = 1("sescase" EQUAL 1("orig" / "term")/ orig-cdiv)
registration-state-param = "regstate" EQUAL 1("unreg" / "reg")
orig-cdiv = "orig-cdiv"
Examples of possible P-Served-User header field:
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P-Served-User: <sip:user@example.com>; orig-cdiv; regstate=reg
or
P-Served-User: <sip:user@example.com>; orig-cdiv
or
P-Served-User: <sip:user@example.com>; sescase=term; regstate=unreg
5. IANA Considerations
The syntax of the P-Served-User header field is defined in [RFC5502]
and updated in Section 4 of this document.
This document requests IANA to update the existing row for the P-
Served-User header field in the "Header Fields" sub-registry:
Header Name Compact Form Reference
------------- ------------ ----------------
P-Served-User none [RFC5502][RFCXXXX]
Note to RFC Editor: Please replace XXXX with the RFC number of this document.
This document requests IANA to add new rows for the P-Served-User
header field parameters in the "Header Field Parameters and Parameter
Values" sub-registry as per the registry created by [RFC3968]:
Header Field Parameter Name Predefined Values Reference
-------------- ---------------- ----------------- -----------------
P-Served-User sescase Yes [RFC5502][RFCXXXX]
P-Served-User regstate Yes [RFC5502][RFCXXXX]
P-Served-User orig-cdiv No [RFCXXXX]
Note to RFC Editor: Please replace XXXX with the RFC number of this document.
6. Security Considerations
The security considerations in [RFC5502] apply.
As the "orig-cdiv" parameter of P-Served-User header field can be
used to trigger applications, it is important to ensure that the
parameter has not been added to the SIP message by an unauthorized
SIP entity.
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7. Acknowledgments
The author wishes to thank the 3GPP community for providing guidance,
input, and comments on the document. Thanks also to Dale Worley for
his careful review of the document.
8. References
8.1. Normative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC3968] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Header Field Parameter Registry for the Session
Initiation Protocol (SIP)", BCP 98, RFC 3968,
DOI 10.17487/RFC3968, December 2004,
<http://www.rfc-editor.org/info/rfc3968>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC7044] Barnes, M., Audet, F., Schubert, S., van Elburg, J., and
C. Holmberg, "An Extension to the Session Initiation
Protocol (SIP) for Request History Information", RFC 7044,
DOI 10.17487/RFC7044, February 2014,
<http://www.rfc-editor.org/info/rfc7044>.
8.2. Informative References
[RFC5502] van Elburg, J., "The SIP P-Served-User Private-Header
(P-Header) for the 3GPP IP Multimedia (IM) Core Network
(CN) Subsystem", RFC 5502, DOI 10.17487/RFC5502, April
2009, <http://www.rfc-editor.org/info/rfc5502>.
[TS.3GPP.24.229]
3GPP, "IP multimedia call control protocol based on
Session Initiation Protocol (SIP) and Session Description
Protocol (SDP);Stage 3", 3GPP TS 24.229 v11.
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[TS.3GPP.29.228]
3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
Signalling flows and message contents", 3GPP TS 29.228
v11.
Author's Address
Marianne Mohali
Orange
Orange Gardens, 44 avenue de la Republique
Chatillon 92326
France
Email: marianne.mohali@orange.com
Mohali Expires July 15, 2017 [Page 9]
