SIPCORE Working Group M. Mohali
Internet-Draft Orange
Updates: 5502 (if approved) May 22, 2018
Intended status: Informational
Expires: November 23, 2018
A P-Served-User Header Field Parameter for Originating CDIV session case
in Session Initiation Protocol (SIP)
draft-ietf-sipcore-originating-cdiv-parameter-02
Abstract
The P-Served-User header field RFC5502 is used to convey the identity
of the served user and the session case that applies to this
particular communication session and application invocation. This
document updated RFC5502 by defining a new P-Served-User header field
parameter, "orig-cdiv". The parameter conveys the session case used
by a proxy when handling an originating session after Call Diversion
(CDIV) services has been invoked for the served user. This document
also fixes the ABNF in RFC5502 and provides more guidance for using
the P-Served-User header field in IP networks.
Status of This Memo
This Internet-Draft is submitted 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
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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 November 23, 2018.
Copyright Notice
Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Basic Use Case . . . . . . . . . . . . . . . . . . . . . 3
1.3. Problem Statement . . . . . . . . . . . . . . . . . . . . 4
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Proxy behavior and parameter handling . . . . . . . . . . . . 4
4. Clarification of RFC5502 procedures . . . . . . . . . . . . . 5
5. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Call Flow Examples . . . . . . . . . . . . . . . . . . . . . 8
7.1. Call diversion case . . . . . . . . . . . . . . . . . . . 8
7.2. Call diversion and privacy . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
1.1. General
The P-Served-User header field [RFC5502] was defined based on a
requirement from 3rd Generation Partnership Project (3GPP) IMS (IP
Multimedia Subsystem) in order to convey the identity of the served
user, his/her registration state and the session case 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].
[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 discusses the applicability and
scope of this new header field parameter, and Section 3 specifies the
proxy behavior for handling the new header field parameter.
Section 4 clarifies some of the [RFC5502] procedures, Section 5
describes the extended syntax and correct the syntax of [RFC5502],
Section 6 registers the P-Served-User header field parameters with
IANA, Section 7 gives some examples and Section 8 discusses the
security properties of the environment where this new header field
parameter is intended to be used.
1.2. Basic 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 from the HSS (Home Subscriber Server) to
this S-CSCF, see [TS.3GPP.29.228]. The user profile contains the
list of actions to be taken by the S-CSCF for the served user
depending on the session direction (originating or terminating) and
the user state (registered or not) in the IMS network. With this
user profile, the S-CSCF determines the current case and apply the
corresponding actions such as forward the request to an AS. At its
turn, the AS has to go through a similar process of determining 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 basic call scenarios, the is no particular issue for the S-CSCF
and AS to know which scenario needs to be realized but in case of
call diversion services for which the session is re-targeted, the
session cases defined in [RFC5502] poses some limitations as
described in the following section.
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1.3. Problem Statement
In 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 AS 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 AS
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 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 History-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 AS 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. Applicability
The use of the P-Served-User header field extensions is only
applicable inside a Trust Domain for P-Served-User header field.
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.
3. Proxy behavior and parameter handling
The following section illustrates how this header field parameter can
be used in a 3GPP network.
For a terminating call, the following steps will be followed:
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1. The S-CSCF receives the initial INVITE request for a terminating
call and determines that the session case is for a terminating
user as described in [RFC5502];
2. The S-CSCF determines who is the served user by looking at the
Request-URI and saves the current Request-URI;
3. The S-CSCF starts the analysis of filter criteria and triggers
the served user AS for the terminating services to be executed by
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;
4. Based on some criteria, the AS 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 and
the AS 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 using the mp-param header field parameter
added in entry associated to the diverted-to address created.
The AS forwards the INVITE request back to the S-CSCF;
5. 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 content by
replacing the "sescase" parameter by the "orig-cdiv" parameter.
The P-Served-User header field value remains unchanged;
6. The S-CSCF forwards 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;
7. When the AS 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).
4. Clarification of RFC5502 procedures
This document provides the following guidance that reminds and
clarifies the P-Served-User header field handling that are missing in
[RFC5502]:
o This header MUST NOT be repeated within a request for a particular
session at a particular time for the reason that session cases are
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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 from [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.
5. Syntax
5.1. 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 [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].
5.2. 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:
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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 = "sescase" EQUAL ("orig"/"term")/ orig-cdiv
registration-state-param = "regstate" EQUAL ("unreg" / "reg")
orig-cdiv = "orig-cdiv"
Examples of possible P-Served-User header field:
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
6. IANA Considerations
The syntax of the P-Served-User header field [RFC5502] is 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]:
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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.
7. Call Flow Examples
7.1. Call diversion case
The following call flow shows a session establishement for Alice
calls Bob which has a call diversion when busy towards Carol.
proxy server UA
Alice Bob's...S-CSCF-B..........AS-B.............Bob Carol
| | | | |
| INVITE F1 | | | |
|--------------->| INVITE F2 | | |
| |--------------->| | |
| | INVITE F3 | | |
| |<---------------| INVITE F4 | |
| |-------------------------------->| |
| | 486 F5 | |
| |<--------------------------------| |
| | 486 F6 | | |
| |--------------->| | |
| | INVITE F7 | | |
| |<---------------| | |
| | INVITE F8 | | |
| |--------------->| | |
| | INVITE F9 | | |
| |<---------------| INVITE F10 |
| |------------------------------------------------->|
| | | | |
| | | | 180 F11 |
| | | 180 F12 |<---------------|
| | 180 F13 |<---------------| |
| 180 F14 |<---------------| | |
|<---------------| | | |
| | | | |
F1 INVITE Alice -> S-CSCF-B
INVITE sip:bob@example.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
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To: Bob <sip:bob@example.com>
F2 INVITE S-CSCF-B -> AS-B
INVITE sip:bob@example.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
F3 INVITE AS-B -> S-CSCF-B
INVITE sip:bob@example.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
F4 INVITE S-CSCF-B -> Bob
INVITE sip:bob@192.0.2.4 SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
F5-F6 486 BUSY Bob -> S-CSCF-B -> AS-B
486 BUSY
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>;tag=es43sd
F7 INVITE AS-B -> S-CSCF-B
INVITE sip:Carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
F8 INVITE S-CSCF-B -> AS-B
INVITE sip:Carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; orig-cdiv; regstate=reg
F9 INVITE AS-B -> S-CSCF-B
INVITE sip:carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; orig-cdiv; regstate=reg
F10 INVITE S-CSCF-B -> Carol
INVITE sip:carol@192.0.2.7 SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
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Figure 1: P-Served-User during call diversion service
7.2. Call diversion and privacy
The following call flow shows a call diversion use case for which
Alice has no identity restriction service and Bob has an
unconditional call diversion service towards Carol and an identity
presentation restriction service.
proxy server UA
Alice Bob's...S-CSCF-B..........AS-B.............Bob Carol
| | | | |
| INVITE F1 | | | |
|--------------->| INVITE F2 | | |
| |--------------->| | |
| | INVITE F3 | | |
| |<---------------| | |
| | INVITE F4 | | |
| |--------------->| | |
| | INVITE F5 | | |
| |<---------------| INVITE F6 | |
| |------------------------------------------------->|
| | | | |
| | | | 180 F7 |
| | | 180 F8 |<---------------|
| | 180 F9 |<---------------| |
| 180 F10 |<---------------| | |
|<---------------| | | |
| | | | |
F1 INVITE Alice -> S-CSCF-B
INVITE sip:bob@example.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
Supported: histinfo
F2 INVITE S-CSCF-B -> AS-B
INVITE sip:bob@example.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Bob <sip:bob@example.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
F3 INVITE AS-B -> S-CSCF-B
INVITE sip:carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Carol <sip:carol@domainc.com>
P-Served-User: <sip:bob@example.com>; term; regstate=reg
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History-Info:
<sip:bob@example.com>;index=1,
<sip:carol@domainc.com;cause=302>;index=1.1;mp=1
F4 INVITE S-CSCF-B -> AS-B
INVITE sip:carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Carol <sip:carol@domainc.com>
P-Served-User: <sip:bob@example.com>; orig-cdiv; regstate=reg
History-Info:
<sip:bob@example.com>;index=1,
<sip:carol@domainc.com;cause=302>;index=1.1;mp=1
F5 INVITE AS-B -> S-CSCF-B
INVITE sip:carol@domainc.com SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Carol <sip:carol@domainc.com>
P-Served-User: <sip:bob@example.com>; orig-cdiv; regstate=reg
History-Info:
<sip:bob@example.com?privacy=history>;index=1,
<sip:carol@domainc.com;cause=302>;index=1.1;mp=1
F6 INVITE S-CSCF-B -> Carol
INVITE sip:carol@192.0.2.7 SIP/2.0
From: Alice <sip:alice@domaina.com>;tag=1928301774
To: Carol <sip:carol@domainc.com>
History-Info:
<sip:bob@example.com?privacy=history>;index=1,
<sip:carol@domainc.com;cause=302>;index=1.1;mp=1
<sip:carol@192.0.2.7>;index=1.1.1;rc=1.1
Figure 2: P-Served-User when privacy requested
8. 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.
9. Acknowledgments
The author wishes to thank the 3GPP community for providing guidance,
input, and comments on the document. Thanks to Dale Worley for his
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careful review of the document and to Paul Kyzivat. A special thanks
to Christer Holmberg.
10. References
10.1. 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,
<https://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,
<https://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,
<https://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,
<https://www.rfc-editor.org/info/rfc7044>.
10.2. 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, <https://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.
[TS.3GPP.29.228]
3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
Signalling flows and message contents", 3GPP TS 29.228
v11.
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Author's Address
Marianne Mohali
Orange
Orange Gardens, 44 avenue de la Republique
Chatillon 92326
France
Email: marianne.mohali@orange.com
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