S-CSCF SELECTION FOR APPLICATION SERVER ORIGINATED

REQUESTS

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority of United States Provisional Patent

Application Serial No. 60/795,582, filed on April 28, 2006 and United States

Provisional Patent Application Serial No. 60/838,899, filed on August 21,

2006. The subject matter of the above referenced applications is

incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to service request handing, and more

particularly to a scenario where an application server initiates a request on

behalf of a subscriber who is not registered with a IP subsystem.

Description of the Related Art

[0002] An IP system, for example, an IP multimedia subsystem (IMS),

utilizes a Session Initiation Protocol (SIP) for initiating and controlling

service requests. Procedures for handling request in IMS are currently

defined and described, for instance, in 3GPP TS 23.228 and 24.229

specifications. Specifically, clause 5.65 of 3GPP TS 23.228 (version 7.2.0)

specification defines a scenario when an application server initiates a request

on behalf of a subscriber who is not currently registered to the IMS. One

important example that uses this scenario is the voice call continuity call

setup described in the 3GPP TR 23.806 (version 7.0.0) and TS 23.206

(version 0.3.0) specifications. In the voice call continuity scenario, when a

call setup is initiated from a circuit switched domain, the call continuity

function, which is an application server from the IMS point of view, is

anchored to the call and it sends the session initiation request to the IMS on

behalf of a calling subscriber who may or may not be registered to the IMS.

[0003] Clause 5.7.3 of 3GPP TS 24.229 (version 7.2.0) specification

describes procedures in the application server for sending requests on behalf

of a subscriber. According to current procedures, the application server

sends the request to the Serving-Call Service Control Function (S-CSCF).

The S-CSCF is an IMS element that provides the session control services for

a mobile node, which enables a network operator to support the services.

Functions provided by the S-CSCF include the management of mobile

registrations, maintaining of the session, interaction with other services,

charging and security. If the subscriber is registered to the IMS, then the

application server learns the address of the S-CSCF where the user is

registered, either from a third party registration procedure or by querying a

home subscriber server. However, no solution is currently provided for the

case where the subscriber is not registered in the IMS.

[0004] According to clause 5.6.5 of the 3GPP TS 23.228 specification, in

cases of originating unregistered procedures, the S-CSCF in the home

subscriber server will follow the same principles as currently defined for

terminating unregistered user. However, as currently defined, to terminate a

call to an unregistered user, it is necessary for the S-CSCF to have

unregistered terminating services. Otherwise, the home subscriber server

will not return capabilities for location query, and thus an Interrogating-Call

Service Control Function (I-CSCF) will reject the request instead of

forwarding it to a terminating S-CSCF. So even though call origination on

behalf of a user can be done even if the user has no originating unregistered

services at all, to terminate a call to unregistered user, it is necessary to have

unregistered terminating services.

SUMMARY OF THE INVENTION

[0005] An embodiment of the invention relates to a server including a

sending unit configured to send a location information request to a home

server for querying a default server name and capabilities of a unregistered

subscriber for whom the server is originating the location information

request. The server also includes a processing unit, if the default server

name is provided in a location information answer, configured to route the

location information request to the default server name provided in the

location information answer or configured to select a suitable function and

the supported capabilities of the selected function. The server further

includes an indicating unit configured to indicate in the location information

request that the function should serve the location information request as an

originating request.

[0006] Another embodiment of the invention relates to an interrogating-call

session control function including a receiving unit configured to receive a

location information request including a public identity of an unregistered

subscriber, the location information request being used to indicate an

originating request. The interrogating-call session control function also

includes a processing unit configured to query a home server for capability

information for the subscriber associated with the public identity and a

sending unit configured to send, upon receipt of a location information

answer from the home server, the location information request to a default

serving function or a selected serving function, depending on information

provided in the location information answer in response to the location

information request.

[0007] Another embodiment of the invention relates a method for sending,

by an interrogation server, a location information request to a home server

for querying a default server name and capabilities of an unregistered

subscriber, receiving, by the interrogation server from the home server, a

location information answer, routing, by the interrogation server, the

location information request to the default server name provided in the

location information answer, if the default server name is provided in the

location information answer, and selecting, by the interrogation server, a

suitable function that support the capabilities of the subscriber, if the default

server name is not provided in the location information answer, wherein the

interrogation server indicates in the location information request that the

function should serve the location information request as on originating

request.

[0008] Another embodiment of the invention relates to a method for

receiving, by an interrogation function from an application server, a location

information request including a public identity of the subscriber, the location

information request being used to indicate an originating request, querying

for a serving function for capability information for the subscriber associated

with the public identity, and sending the location information request to a

default serving function or a selected serving function depending on

information provided in a location information answer in response to the

location information request.

[0009] Another embodiment of the invention relates an apparatus including

sending means for sending, by an interrogation server, a location

information request to a home server for querying a default server name and

capabilities of an unregistered subscriber, receiving means for receiving, by

the interrogation server from the home server, a location information

answer, routing means for routing, by the interrogation server, the location

information request to the default server name provided in the location

information answer, if the default server name is provided in the location

information answer, and selecting means for selecting a suitable function

that support the capabilities of the subscriber, if the default server name is

not provided in the location information answer, wherein the interrogation

server indicates in the location information request that the function should

serve the location information request as on originating request.

[0010] Another embodiment of the invention relates an apparatus including

receiving means for receiving, by an interrogation function from an

application server, a location information request including a public identity

of the subscriber, the location information request being used to indicate an

originating request, querying means for querying, by the interrogation

function, for a serving function for capability information for the subscriber

associated with the public identity, and sending means for sending, by the

interrogation function, the location information request to a default serving

function or a selected serving function depending on information provided in

a location information answer in response to the location information

request.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0011] The accompanying drawings, which are included to provide a further

understanding of the invention and are incorporated in and constitute a part

of this specification, illustrate embodiments of the invention that together

with the description serve to explain the principles of the invention, wherein:

[0012] Figure 1 illustrates an embodiment of an IP Multimedia subsystem;

[0013] Figure 2 illustrates steps implemented by a server implementing an

embodiment of the invention; and

[0014] Figure 3 illustrates steps implemented by the I-CSCF implementing

an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Reference will now be made to the preferred embodiments of the

present invention, examples of which are illustrated in the accompanying

drawings.

[0016] Figure 1 illustrates an embodiment of an IP Multimedia subsystem

100 in which embodiments of the present invention may be implemented.

Subsystem 100 includes an application server layer 102, a session control

layer 104 and a transport and endpoint layer 106. Subsystem 100 is a

unified architecture that supports a wide range of services enabled by the

flexibility of a Session Initiation Protocol (SIP). As shown in Figure 1, the

subsystem 100 can support multiple application servers providing traditional

telephony services 108 and non-telephony services 110, such as instant

messaging, push-to-talk, and video streaming. Transport and endpoint layer

106 initiates and terminates SIP signalling to set up sessions and provide

bearer services such as, conversion of voice from analog or digital formats

to Internet Protocol (IP) packets using Realtime Transport Protocol (RTP).

Session control layer 104 includes a Call Session Control Function (CSCF)

112, which provides the registration of endpoints and routing of SIP

signalling messages to an appropriate application server. CSCF 112

interworks with transport and endpoint layer 106 to guarantee Quality of

Service across all services. Session control layer 104 also includes a Home

Subscriber Server (HSS) database 114 that maintains the unique service

profile for each end user. The end user's service profile stores all of the user

service information and preferences in a central location, including an end

user's current registration information, roaming information, telephony

services, such as call forwarding information, instant messaging service

information, such as buddies list, and voice mail box options. Application

server layer 102 includes the application servers, which provide the end-user

service logic.

[0017] According to a first embodiment of the present invention, when the

application server originates a request on behalf of an unregistered IMS

subscriber, the application server sends a location information request

message to the home subscriber server, through an existing Sh interface, for

querying a default server name and the capabilities of the subscriber. It

should be noted that the capabilities may be mandatory or optional. If the

default server name is provided in a location information answer/response,

then the request is routed to the default server name, otherwise, the

application server selects, based on the received capabilities in the location

information answer, a suitable Serving Call Session Control Function (S-

CSCF) in the network and their supported capabilities. This information is

configured to the application server. The application server indicates in the

SIP message that the S-CSCF should serve the request as an "originating"

request by putting an ORIG parameter to URI of the S-CSCF.

[0018] The 3GPP 29.228 (version 7.0.0) specification discloses procedures

in the home subscriber server for responding to the location information

request. According to current procedures, if the subscriber is not registered

in the IMS, then the home subscriber server sends a Server-Capablities

Attribute Value Pair (AVP), as required for S-CSCF selection, in the

location information answer message only if unregistered services are

provisioned for the user. This causes the application server's originating

request to fail for such users who do not any services that should run in an

unregistered state. As such, in a first solution implemented in the first

embodiment of the present invention, the I-CSCF indicates to the home

subscriber server, in a location information request message, that a location

information query is being made for the originating request. If the

subscriber, in this embodiment, is not registered to the IMS, then the home

subscriber server provides the Server-Capabilities AVP in the location

information response message, for such location information request

message that includes an indication of the originating scenario, even if the

subscriber does not currently have "originating" unregistered services. In a

second solution implemented in the first embodiment of the invention, if the

subscriber is not registered to the IMS, then the home subscriber server

always provides the Server-Capabilities AVP in a location information

response message, even if the subscriber does not have current unregistered

services.

[0019] In a second embodiment of the invention, the application server

sends the request to the I-CSCF and inserts a public identity of the

subscriber in a P-Asserted-Identity header, as required by the disclosure of

clause 5.7.3 of the 3GPP 24.229 specification. The application server

indicates to the I-CSCF that this is an originating request. I-CSCF,

recognizing that the originating request is being served, queries the home

subscriber server for capability information for the subscriber indicated in

the P-Asserted-Identity header of the SIP request. That is, I-CSCF sends the

location information request message to the home subscriber server through

a Cx interface using the identity from P-Asserted-Identity header, instead of

a Request-URI as in a terminating case, to the Public-Identity AVP of Cx

message. When the I-CSCF receives a response from the home subscriber

server in the location information answer message, the I-CSCF either sends

the request to the default S-CSCF or selects a S-CSCF based on the

capabilities according to normal procedure. I-CSCF indicates in the SIP

message that the S-CSCF should serve the request as an "originating"

request, by placing an ORIG parameter to URI of S-CSCF. Alternatively,

when the application server sends the SIP request to the I-CSCF, the

application service adds and ORIG parameter to the URI of the I-CSCF that

is added to the SIP message as the topmost route header.

[0020] Even in the second embodiment of the invention, the I-CSCF

indicates to the home subscriber server in the location information request

message that a location information query is being made for the originating

request. If the subscriber, in this embodiment, is not registered to the IMS,

then in a first solution implemented in the second embodiment, the home

subscriber server provides Server-Capabilities AVP in a location

information response message, for such location information request

message that includes an indication of the originating scenario, even if the

subscriber does not have "originating" unregistered services. In the second

solution implemented in the second embodiment of the invention, if the

subscriber is not registered to the IMS, then the home subscriber server

always provides the Server-Capabilities AVP in a location information

response message, even if the subscriber does not have unregistered

services. To implement the second solution, no extensions of Cx messages

are needed, as the only change is in the home subscriber server's behaviour.

No change is also needed in the I-CSCF procedures of handling the location

information answer messages, thus this solution is backward compatible for

I-CSCF.

[0021] One possible method for implementing the second embodiment of

the invention is for the application server to indicate an originating scenario

to the I-CSCF by putting the ORIG flag as a URI parameter in a Request-

URI of SIP message. The Request-URI of SIP message is parsed by the I-

CSCF according to normal I-CSCF procedures. If this method is used, then

the I-CSCF removes the ORIG flag from the Request-URI of SIP message.

[0022] In the second embodiment, operators may define a dedicated I-CSCF

(configured in application servers) that serves only originating requests for

unregistered services and that does not have S-CSCF selection based

capabilities. In the application server, is must be ensured that the I-CSCF

supports this functionality.

[0023] Another possible implementation method of the second embodiment

is to define a new SIP header or define a new parameter for the P-Asserted-

Identity header, which includes an identifier of the subscriber. If this

method is chosen, then the I-CSCF has to parse the additional SIP header as

part of its normal procedure in order for it to decide if the originating request

is being served. The location information request message of the Cx

interface should be extended with a new AVP that includes an indication of

whether the location information request is made for an originating request.

The new AVP may be optional, thus an I-CSCF not supporting the extension

of the Cx interface may still work with this solution. Another alternative is

to extend the existing Public-Identity AVP with the information on whether

a location information query is requested for the originating request.

[0024] The first embodiment requires that the S-CSCFs addresses and the

capabilities supported by those S-CSCFs are configured to each application

server that would like to originate requests on behalf of a subscriber. Also,

the same S-CSCF selection logic is implemented to each application server,

otherwise already available in the I-CSCF. With the first embodiment, one

less role is involved in processing of originating requests and no

modification is needed to the SIP. However, configuring S-CSCF

information to the applications server might not be preferred by operators

due to trust issues.

[0025] The second embodiment relies on the I-CSCF's existing capability

for the S-CSCF selection. No additional configuration is needed for the

application server, no capability based S-CSCF selection is needed in the

application server, although change is required in the SIP protocol and in I-

CSCF behaviour. The first solution implemented in the first and second

embodiments requires introduction of new AVP or change of existing

Public-Identity AVP to the location information request Cx message. In this

solution, change is required both in the I-CSCF and home subscriber server

implementation, thus this solution is not backward compatible for the I-

CSCF and home subscribe server. The second solution implemented in the

first and second embodiments does not require change in the Cx message; it

only requires change in the home subscriber server's implementation; thus,

this solution is backward compatible for the I-CSCF.

[0026] Figure 2 illustrates steps implemented in a server implementing the

invention. In Step 2010, the I-CSCF sends a location information request to

a home subscriber server for querying a default server name and capabilities

of an unregistered subscriber. In Step 2020, the I-CSCF receives, from the

home server, a location information answer. In Step 2030, the I-CSCF

routes the location information request to the default server name provided

in the location information answer, if the default server name is provided in

the location information answer. In Step 2040, the I-CSCF selects a suitable

function that support the capabilities of the subscriber, if the default server

name is not provided in the location information answer, wherein the

interrogation server indicates in the location information request that the

function should serve the location information request as on originating

request.

[0027] Figure 3 illustrates the steps implemented by the I-CSCF

implementing the invention. In Step 3010, the I-CSCF receives, from an

application server, a location information request including a public identity

of the subscriber, the location information request being used to indicate an

originating request. In Step 3020, the I-CSCF queries for a serving function

for capability information for the subscriber associated with the public

identity. In Step 3030, the I-CSCF sends the location information request to

a default serving function or a selected serving function depending on

information provided in a location information answer in response to the

location information request.

[0028] It should be appreciated by one skilled in art, that the present

invention may be utilized in any device that implements the network

availability information described above. The foregoing description has

been directed to specific embodiments of this invention. It will be apparent;

however, that other variations and modifications may be made to the

described embodiments, with the attainment of some or all of their

advantages. Therefore, it is the object of the appended claims to cover all

such variations and modifications as come within the true spirit and scope of

the invention.