Abstract:
The present invention provides a method for notifying a roaming or home network that a client associated with the home network has registered with a roaming network. A client of a home network registers with a roaming network. The roaming network alerts the home network of the registration of the client. The home network sends a message to an application. The message indicates that the client has registered with the roaming network. Messages for the roaming client can now be routed directly to the roaming network without having to first pass through the home network.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to mobile communication systems, and more particularly to a method for registering roaming mobile units. 
       BACKGROUND OF THE INVENTION 
       [0002]    One attractive feature of mobile cellular communication systems is that they allow mobile users of the systems the ability to move. Mobile users may move within their own network, or they may be able to place an receive calls while located in a network distinct from their own. The ability to place and receive calls while located in a non-home network is often referred to as “roaming.” The ability to roam allows mobile users a much greater service area. 
         [0003]    A roaming mobile unit is required to register with any network to which it communicates. However, most current communication systems do not pass location information like the IP address or accessing nodes P-CSCF (Proxy-Call Session Control Function) address of a roaming mobile unit to the home or visiting network applications during registration. This leads to delays for the home network or an application in the home network in communicating with the roaming mobile unit, since the home network has to actively search for a roaming mobile unit prior to sending a message to the roaming mobile unit. 
         [0004]    Therefore, a need exists for a method of facilitating communication between a home communication network and a mobile unit that is currently roaming. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a method for notifying a client-registering event to the home network of the mobile unit and to the roaming network. The client, preferably an IMS client, roams to a network that is not its home network. The client registers with this roaming network, typically by sending a registration message. In accordance with an exemplary embodiment of the present invention, the registration message includes the IP address of the client, the address of the P-CSCF of the roaming network, and SIP x-header fields. 
         [0006]    The P-CSCF receives information relating to the roaming client. This is preferably accomplished by forwarding the registration information to an I-CSCF (Interrogating-CSCF) within the home network. The registration information can alternately be sent to an IBCF. The I-CSCF or IBCF in the home network looks up the client in a database, such as an HSS. The HSS returns the information about the client&#39;s S-CSCF (Service-CSCF) in the home network to the I-CSCF. The I-CSCF then forwards the REGISTER message to the S-CSCF. This is preferably accomplished by sending the information to an S-CSCF of the home network. 
         [0007]    Upon receiving an indication that the client is located in the roaming system, an S-CSCF at the home network preferably sends a message to an application. The application can be located within the home network or external to the home network. The message sent to the application preferably includes contact information for the IMS client that has been extracted from the registration message. 
         [0008]    The message sent to the application preferably includes an indication that the client has registered with the roaming network and provides an enhanced registration notification to the application. The enhanced notification preferably includes SIP headers, the IP address of the client, and the P-CSCF address of the newly registered client. 
         [0009]    The application preferably includes data related to the current location of the roaming client. In an exemplary embodiment, the address of the client is the address of the P-CSCF of the roaming network. The address of the client can also be the IP address of the client or the PDSN Home IP address of the client. The application has the capability to notify other applications that register for notification of incoming client registrations. 
         [0010]    The application can notify other applications. This is preferably done by registering the other applications with the application that receives information relating to the current location of a roaming client. Upon receiving updates about a roaming mobile unit, the application then notifies the registered applications to the location of the roaming client. Messages sent to these registered clients may include the IP address of the roaming client, the P-CSCF of the roaming network, or SIP optional x-header fields. 
         [0011]    In accordance with an exemplary embodiment, when the client deregisters from the roaming network, the application is notified of the deregistration utilizing the standard IMS protocol. The application then notifies the other applications that registered for updates to the location of roaming mobile units. 
         [0012]    An exemplary embodiment of the present invention thereby allows the application to route directly to the client utilizing the IP address of the client or the address of the P-CSCF of the roaming network without having to route the message through the S-CSCF of the home network. This reduces delays for applications in either the home network or the roaming network when communicating with the client, especially while roaming. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0013]      FIG. 1  depicts an IMS core network in accordance with an exemplary embodiment of the present invention. 
           [0014]      FIG. 2  depicts a flowchart of a method for notifying an application of a client registering in a roaming network in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention can be better understood with reference to  FIGS. 1 and 2 .  FIG. 1  depicts an IMS core network  100  that includes a home network  101 , a roaming network  103 , a Home Subscriber Server (HSS)  105 , and a client  107 . 
         [0016]    Networks  101  and  103  are responsible for call and session control provided by the IMS in a subscriber&#39;s home network. Networks  101  and  103  manage SIP sessions, provides features and services, coordinates with other network elements for session control, and allocates media resources. 
         [0017]    IMS networks  101  and  103  each include a plurality of functions and components, which may be installed on separate servers or can alternately share the same server. This allows for flexible packaging for various customer needs. IMS network  101  comprises S-CSCF (Serving-CSCF)  111 , I-CSCF (Interrogating-CSCF)  121 , P-CSCF (Proxy-CSCF)  131 , and applications  141  and  151 . Roaming IMS network  103  comprises S-CSCF  113 , I-CSCF  123 , P-CSCF  133 , and applications  143  and  153 . 
         [0018]    S-CSCF  111  manages SIP sessions and coordinates with other network elements for call/session control. S-CSCF  111  performs SIP registration, session control, service control, call monitoring, and security. SIP registration comprises processing SIP REGISTER requests and maintaining subscriber data and state information for the duration of the registration session. Session control comprises performing call/session setup, modification, and termination. Service control comprises interaction with Application Services platforms for the support of features and services. Call monitoring comprises call monitoring and recording for accounting and other related services. Security comprises providing security for the session. 
         [0019]    SIP user clients communicate to the various application servers via S-CSCF  111 . S-CSCF  107  provides the messaging filtering, message forwarding, and transaction and session control functions for the sessions initiated by SIP signaling. S-CSCF  111  also allows the various SIP-based application servers to communicate with each other. S-CSCF  111  also preferably provides SIP proxy functions for forwarding SIP messages to the proper application server and allowing application servers to subscribe to SIP dialogs between SIP clients and servers. 
         [0020]    Because S-CSCF  111  supports standard SIP messages, the user clients and SIP application servers can span a wide variety of telephony and non-telephony services. For example, S-CSCF  111  can provide the message filtering and forwarding for SIP-based services such as Instant Messaging (IM), Push-To-Talk, and multimedia services. 
         [0021]    I-CSCF  121  is the contact point within network  101  for all connections destined to a subscriber connected to network  101  or a roaming subscriber currently located within the service areas supported by network  101 . Network  101  may include multiple I-CSCFs. I-CSCF  121  assigns an S-CSCF to a user performing SIP registration. I-CSCF  121  also obtains from HSS  105  the address of S-CSCF  111  and uses the address to route a SIP request or response received from a network towards S-CSCF  111 . 
         [0022]    P-CSCF  131  is preferably the first contact for a SIP mobile unit to gain access to network  101  from the access packet network domain. P-CSCF  131  provides the necessary SIP routing capability between SIP mobiles and network  101 . P-CSCF  131  also coordinates with the access network to authorize the resources and Quality-of-Service (QoS). For services that are offered by the home IMS network, P-CSCF  131  relays the SIP signaling to the IMS server in the home network. 
         [0023]    HSS  105  is the master subscriber database for system  100  and includes registration status and subscription data for users. The data within HSS  105  is used by the different network core functional entities in IMS  100  when processing subscribers. HSS  105  includes user data that can be downloaded to S-CSCF  111  and S-CSCF  113 . HSS  105  stores temporary data with the location of S-CSCF  111  where the user is currently registered. 
         [0024]    Client  107  is a subscriber device that is preferably capable of placing and receiving calls within system  100 , either by utilizing home network  101  or, when roaming, by utilizing roaming network  103 . 
         [0025]    Elements in roaming network  103  perform similar functions to similarly-names elements in home network  101 . 
         [0026]      FIG. 2  depicts a flowchart  200  of a method for notifying a home network of a client registering in a roaming network in accordance with an exemplary embodiment of the present invention. 
         [0027]    In accordance with an exemplary embodiment, IMS client  107  has home network  101  as its home network. IMS client  107  registers ( 201 ) with roaming P-CSCF  133  by sending a registration message. In a typical network, P-CSCF  133  is unaware of the home system of IMS client  107 . In an exemplary embodiment, the registration message includes the IP address of client  107 , the address of P-CSCF  133 , and optional SIP x-header fields. 
         [0028]    P-CSCF  133  passes ( 203 ) registration information to I-CSCF  123 . P-CSCF also passes ( 205 ) registration information to I-CSCF  121 . I-CSCF  121  looks up ( 207 ) client  107 , preferably utilizing Diameter, in HSS  105 . 
         [0029]    HSS  105  passes ( 209 ) the information relating to client  107  to I-CSCF  121 . The information includes the address of S-CSCF  111 . I-CSCF  121  forwards ( 211 ) registration information to S-CSCF  111 . 
         [0030]    Upon receiving an indication that client  107  is located in roaming system  103 , S-CSCF  111  preferably sends ( 213 ) a message to application  141 . S-CSCF  111  preferably extracts the contact information of IMS client  107  from the registration message. In an exemplary embodiment, this information replaces the address of S-CSCF  111 . In an exemplary embodiment, S-CSCF  111  can send the message to multiple applications. 
         [0031]    The message includes an indication that client  107  has registered with roaming network  103 . The message preferably provides an enhanced application notification to application  141 . The enhanced application notification preferably includes SIP headers, the IP address of client  107 , and P-CSCF  133  of the newly registered network. 
         [0032]    Application  141  includes data related to the current location of roaming client  107 . In an exemplary embodiment, the address of client  107  is the address of P-CSCF  133 . In a further exemplary embodiment, the address of client  107  is the IP address of client  107 . In a further exemplary embodiment, the address of client  107  is the PDSN Home IP address of client  107 . 
         [0033]    Additionally, application  141  has capability to notify other applications that register for notification of incoming client registrations. Application  141  preferably determines if client  107  is roaming by checking either the incoming IP address of the client or domain of the P-CSCF. 
         [0034]    Application  141  in home network  101  can notify other applications in home network  101 . In accordance with an exemplary embodiment, other applications at home network  101  register with application  101  if they want to be updated with the registration status of roaming clients. Messages sent to other applications can include the IP address of the roaming client, the P-CSCF of the roaming network, or SIP xhdr fields. This allows application  141  to route directly to client  107  utilizing the IP address of client  107  or the address of P-CSCF  133  without passing through the S-CSCF  111 . This reduces delays for applications in either home network  101  or roaming network  103  when communicating with the client  107 . 
         [0035]    In accordance with an exemplary embodiment, when client  107  deregisters from network  103  application  141  is notified of the deregistration utilizing the standard IMS protocol. Application  141  then preferably notifies other applications, such as application  151 , application  153 , and application  143 . 
         [0036]    While this invention has been described in terms of certain examples thereof, it is not intended that it be limited to the above description, but rather only to the extent set forth in the claims that follow.