P-Served-User Header Field
Parameter for Originating CDIV session case in Session Initiation Protocol
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Transport
5502P-3GPPIMSThis specification defines a new Session Initiation Protocol (SIP)
P-Served-User header field parameter, "orig-cdiv-param", which 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 . The P-Served-User header field conveys the identity
of the served user and the session case that applies to this particular
communication session and application invocation.This document
updates in order to add the originating after
CDIV session case.The P-Served-User header field was defined in 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
.This header field conveys the
identity of the served user and the session case that applies to this
particular communication session and application
invocation. 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. The generic-param of the P-Served-User is
extended by the "orig-cdiv-param" created as a new parameter for this
Originating_CDIV session case. The following
section defines the orig-cdiv-param P-Served-User header field
parameter usage, Section 2 specifies the proxy behavior for the new
header field parameter handling, and Section 3 discusses the
applicability and scope of this new header field parameter. Section 4
descibes the Syntax, Section 5 registers the orig-cdiv header field
parameter with the IANA, and Section 6 discusses the security
properties of the environment where this new header field parameter is
intended to be used.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, a user profile
is downloaded to the S-CSCF from the HSS (Home Subscriber Server), see
.To be able to
determine which responsibilities the S-CSCF and the Application Server
haves to perform and on which user’s behalf, it is necessary to
know in which situation is the session and who is the current served
user. defines 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 iFC 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, 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 but this is not the case.
Indeed, the originating user remains the same and the diverting
user’s originating services do not have to be triggered as if it
was an originating call. For instance, the originating user identity
should not be hidden because the diverting user has a privacy service
for his/her own identity. In the same manner, some specific services
may be triggered when performing a call diversion that would not be
for a normal originating call. For this particular use case,
this document created a new parameter to be embedded in the
P-Served-User header field.The orig-cdiv-param header filed parameter can be used inside a trust
domain 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 determines
that the session case is for a terminating user as described in , then it determines the served user by looking at the
Request-URI and saves this Request-URI. Then, the S-CSCF starts the iFC
processing and triggers the served user Application Server for the
terminating services to be executed.Based on
some criteria, the diversion service concludes that the request needs to
be diverted to another user or application and the received Request-URI
is replaced with the new diverted-to address. The Application Server
stores the Request-URI(s) by adding one or two new History-Info header
field entry(ies) . The served user address is
tagged thanks to the mp-param header field parameter added in the
History-Info entry associated to the diverted-to address created.
Then the AS forwards the INVITE request back to the S-CSCF.
When the S-CSCF receives the INVITE, it can see
that the topmost Route header contains its own hostname but the
Request-URI does not match the saved Request-URI. In that case, the
S-CSCF updates the P-Served-User header field content by removing both
"sescase" and "regstate" header field parameters and inserting the
"orig-cdiv" header field parameter.Then the
procedure would continue forwarding the INVITE request over to an AS
that hosts the originating services of the served user that specifically
need to be executed on the forwarded leg after a call diversion service.
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 served user.The use of the P-Served-User header field extensions is only
applicable inside a Trust Domain for 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.The orig-cdiv-param parameter is defined as an instance of
generic-param from the current served-user-param component of
P-Served-User header field.Following is a
reminder of the P-Served-User syntax: EQUAL, HCOLON, SEMI, name-addr, addr-spec, and generic-param are
defined in .The augmented Backus-Naur Form (BNF)
syntax of the P-Served-User header field is described in .The P-Served-User header syntax is
extended as follows:The following is an example of a P-Served-User header field:
P-Served-User: <sip:user@example.com>;
orig-cdiv; regstate=regThis specification defines a new P-Served-User header field parameter
called orig-cdiv-param in the "Header Field Parameters and Parameter
Values" sub-registry as per the registry created by .The syntax is defined in Section 4. The required information is:Note to RFC Editor: Please replace RFC XXXX with the RFC number of
this specification.The security considerations in apply.As the orig-cdiv-param P-Served-User header field
parameter 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.TBDKey words for use in RFCs to Indicate Requirement
LevelsSIP: Session Initiation ProtocolThe Internet Assigned Number Authority (IANA) Header Field
Parameter Registry for the Session Initiation Protocol (SIP)Augmented BNF for Syntax Specifications: ABNFAn Extension to the Session Initiation Protocol (SIP) for
Request History InformationThe SIP P-Served-User Private-Header (P-Header) for the 3GPP
IP Multimedia (IM) Core Network (CN) SubsystemIP multimedia call control protocol based on Session
Initiation Protocol (SIP) and Session Description Protocol
(SDP);Stage 33GPPIP Multimedia (IM) Subsystem Cx and Dx interfaces; Signalling
flows and message contents3GPP