Abstract:
A method for supporting an inbound roaming subscriber in an IMS network, comprises receiving a request from the inbound roaming subscriber to access the IMS network, determining the inbound roaming subscriber&#39;s home network, retrieving authentication credentials from the inbound roaming subscriber&#39;s home network, and verifying the authentication credentials, dynamically deriving public and private user identities for the inbound roaming subscriber, and creating and storing a subscriber record for the inbound roaming subscriber.

Description:
RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/829,843 filed on May 31, 2013. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a system and method for system and method for visiting subscriber server (VSS) in IMS (IP Multimedia Subsystem) core networks. 
       BACKGROUND 
       [0003]    The Third Generation Partnership Project (3GPP) unites six telecommunications standards bodies, known as “Organizational Partners,” and provides their members with a stable environment to produce the highly successful Reports and Specifications that define 3GPP technologies. A mobile device, also called a User Equipment (UE), may operate in a wireless communication network that provides high-speed data and/or voice communications. The wireless communication networks may implement circuit-switched (CS) and/or packet-switched (PS) communication protocols to provide various services. For example, the UE may operate in accordance with one or more of an Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA: includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR) cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long-Term Evolution (LTE) is a new release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in specification documents from an organization named “3rd Generation Partnership Project” (3GPP). These various radio technologies and standards are known in the art. 
         [0004]    The IMS (IP Multimedia Subsystem) as defined by 3GPP is an all-IP architecture for offering multimedia services such as Voice over IP (VoIP). The IMS core network includes the Call Session Control Function (CSCF) and the Home Subscriber Server (HSS). The CSCF facilitates session setup and teardown using SIP (Session Initiation Protocol). HSS plays the role of a location server in IMS and also serves as a repository for subscriber data. CSCF is divided into three logical entities: Proxy CSCF (P-CSCF), Interrogating CSCF (I-CSCF), and Serving CSCF (S-CSCF). P-CSCF is responsible for routing incoming SIP messages to the IMS registrar server and for facilitating policy control. I-CSCF acts as an inbound SIP proxy server in the IMS. S-CSCF is the heart of the IMS core network. It facilitates the routing path for mobile originated or terminated session requests and is the most processing intensive node of the IMS core network. 
         [0005]    IMS core networks are defined to support home subscribers only, unlike legacy circuit switched (CS) core networks that support both home subscribers as well as inbound roamers. An inbound roamer is a subscriber with its home defined in an operator X&#39;s communication network roaming in or visiting operator Y&#39;s communication network, where operator X and operator Y have a roaming agreement to allow this. In such a scenario, operator Y is able to get roaming revenue, as these inbound roamers are charged extra fees to use operator Y&#39;s network. These are typically called “roaming charges.” 
         [0006]    With LTE (Long-Term Evolution) access and IMS core networks, inbound roamers are supported on radio access. However, only voice over LTE (VoLTE) services are available if the inbound roamer&#39;s home network supports an IMS core network and relevant application servers (AS). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a simplified block diagram of an exemplary network architecture according to the present disclosure; 
           [0008]      FIG. 2  is a simplified block diagram of an exemplary system and method for a visiting subscriber server in an IMS core network; 
           [0009]      FIG. 3  is a simplified block diagram of another exemplary system and method for a visiting subscriber server in an IMS core network; 
           [0010]      FIG. 4  is a simplified flowchart of an exemplary registration method for a visiting subscriber server in an IMS core network; 
           [0011]      FIG. 5  is a simplified flowchart of an exemplary mobile originated method for a visiting subscriber server in an IMS core network; and 
           [0012]      FIG. 6  is a simplified flowchart of an exemplary mobile terminated method for a visiting subscriber server in an IMS core network. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  is a simplified block diagram of an exemplary network architecture according to the present disclosure. A mobile device, referred to as User Equipment (UE)  10 , has traveled away from its home network  12 , a GSM (Global System for Mobile Communications) core network, and roaming in a visited network  14 , which is an IMS (IP Multimedia Subsystem) core network. The two networks  12  and  14  are managed and operated by two independent network operators who have an agreement in place to service each other&#39;s subscribers. The UE  10  is connected to the EPC (Evolved Packet Core) over E-UTRAN (Evolved UMTS Terrestrial Radio Access Network)  16 . The EPC includes the Mobility Management Entity (MME)  18 , which is the key control-node for the LTE access-network. It handles signaling related to mobility and security for E-UTRAN access. The MME  18  is coupled to the Home Subscriber Server (HSS)/Home Location Register (HLR)  19  in the home network  12  via an S6a interface. The HSS/HLR  19  is a central database that contains user-related and subscription-related information. It also provides support functions in mobility management, call and session setup, user authentication and access authorization. The EPC further includes Serving-Gateway (S-GW) and PDN (Packet Data Network) Gateway (P-GW)  20  coupled to the E-UTRAN  16 , MME  18 . The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3GPP technologies. The PDN Gateway provides connectivity from the UE to external packet data networks by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PGW for accessing multiple PDNs. The PGW performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening. 
         [0014]    The EPC is connected to external networks, such as the IP Multimedia Core Network Subsystem (IMS) in the visited network  14 . The visited network  14  further includes network functions P-CSCF (Proxy-Call Session Control Function)  21 , I-CSCF (Interrogating-Call Session Control Function), and S-CSCF (Serving-Call Session Control Function). I-CSCF and S-CSCF are shown here as a combined network node I/S-CSCF  22  to service inbound roaming subscribers. Those subscribers that are in their home IMS network are serviced by the network operator&#39;s I-CSCF and S-CSCF network nodes (not shown). Inbound roaming subscribers are also serviced by Telephony Application Servers (TAS)  23  to provide advanced supplementary and IN (Intelligent Network) services. 
         [0015]    Further provisioned is a novel Visiting Subscriber Server (VSS) node or function  28  that is also connected to the HSS/HLR  19  via a MAP interface. As shown in  FIG. 1 , the VSS functionality  28  may reside within an HSS network node. A MGCF/IBCF (Media Gateway Controller Function/Interconnection Border Control Function)  30  is further coupled to the I/S-CSCF  22  to enable the IMS network to communicate with circuit switched circuits. Operations of the network components are described in more detail below. The VSS is used to support visiting subscribers in the IMS core network. 
         [0016]    In an alternate visited network architecture, an IMS Centralized Services Gateway (ICS GW) may be used to connect legacy GSM/UMTS access networks (and thus legacy GSM/UMTS mobile devices) with an IMS core network. The ICS GW may make the UE appear as an IMS UE to the IMS core network. The ICS GW would be coupled to the I/S-CSCF, which is then connected to the VSS. The ICS GW in the visited network terminates the CS access interfaces, and the UE is interworked to the IMS core in the visited network. The VSS is also used in this architecture to support visiting CS subscribers in the IMS core network. 
         [0017]      FIG. 2  is a simplified block diagram of an exemplary system and method for a visiting subscriber server functionality  28  in the IMS core network. Shown in  FIG. 2  is a system architecture  40  of IMS core network components including the VSS functionality  28  within the HSS  28 ′.  FIG. 2  also depicts a I/S-CSCF  22  which may include a Cx interface to the HSS  28 ′ and/or the VSS  28 . Also, the HSS  28 ′ communicates with the HLR  180  via a MAP interface. 
         [0018]    With reference now to  FIG. 3 , a block diagram of a system architecture  50  of IMS core network components illustrates yet another embodiment of a VSS. VSS  28  is illustrated as being physically separate from the HSS  28 ′.  FIG. 3  also depicts the I/S-CSCF  22  which includes a Cx interface to the HSS  28 ′ and the VSS  28 . The VSS  28  communicates with the HLR  26  via a MAP interface. 
         [0019]    As is known, the HSS functions statically with preconfigured subscriber information and all data necessary to provide access to the IMS such as telephone numbers, authentication criteria, etc. In these exemplary embodiments, the VSS effectively and dynamically creates similar public and/or private records for visiting subscribers. Rather than being pre-populated with the subscriber records maintained by the HSS, embodiments of the VSS function dynamically to create temporary subscriber records corresponding to inbound roaming subscribers to provide access to the IMS core network. 
         [0020]    At the time of a subscriber registering with the IMS core network, the user profile is downloaded to the S-CSCF, where the user profile is stored during the registration procedure. A part of this profile is a list of Initial Filter Criteria (iFC). The iFC contain information about application servers (AS) to be involved in the signaling path for sessions and/or standalone requests to furnish services to the user. These AS are involved in SIP message forwarding via the ISC (IP Multimedia Service Control) interface. The conditions for the AS to be invoked (e.g., based on message content) are referred to as the filter rules. Each time value added services need to be executed, iFC processing performed by the S-CSCF enables Applications Servers to be put in the route of the SIP dialog. This means that S-CSCF will forward the SIP message to the first AS (the one with the highest priority) for which iFC trigger point is satisfied. The IMS network includes a plurality of AS nodes to provide advanced services, and one or more TAS nodes or functions are provided to service inbound roaming subscribers. 
         [0021]    To authenticate a visiting subscriber to have access to a network such as an LTE network, the VSS obtains authentication credentials in a dynamic manner by obtaining the authentication credentials from a HLR that resides in the visiting subscriber&#39;s home network. After authentication, the visiting subscriber is registered with the IMS core of the current or visited network. During the IMS procedures, a temporary subscriber record is created and stored in the VSS. The storage may be performed via memory, database, etc. The VSS may have its own database or it may share a database with other components within the network such as the HSS. 
         [0022]    Embodiments of the VSS may preferably store information persistently, i.e., via geographic redundancy, for back-up purposes in case of, for example, catastrophic failure. In other words, the VSS preferably has the same reliability as the HSS with storage and retrieval of subscriber information. 
         [0023]      FIG. 4  is a simplified flowchart of an exemplary registration method  60  for a visiting subscriber server in an IMS core network. Referring to  FIG. 1  along with references to  FIG. 4 , the visiting subscriber (UE  10 ) attempts to access the current network  14 , as shown in block  62 . The UE may send an attach request that may be a combined EPS/IMSI (Evolved Packet System/ International Mobile Subscriber Identity) attach request to the EPC. After successful attachment, the UE sends a request to access the network that may take the form of a SIP registration message. The SIP registration message may include the user&#39;s MSISDN (Mobile Station International Subscriber Directory Number) and/or IMSI (International Mobile Subscriber Identity), for example. The registration request also includes an identification of the subscriber&#39;s home network, e.g., the home domain name. The registration request is routed to P-CSCF, which routes the request to the inbound roaming I/S-CSCF  22 . Standard Cx protocol is used between I/S-CSCF  22  and VSS  28 . Further, the VSS  28  also dynamically derive the IMS public and private user identities for the inbound roaming subscriber using the MSISDN and IMSI. 
         [0024]    In block  64 , authentication for the visiting subscriber  10  to access the current network  14  is initiated. In block  66 , the VSS  28  obtains authentication credentials such as AKA (Authentication and Key Agreement) vectors dynamically from an HLR  26  that resides in the visiting subscriber&#39;s home network  12 . The VSS  28  may send a MAP Send Authentication Info (SAI) message to the HLR. After successful authentication, registration of the visiting subscriber  10  with the IMS core network is performed in block  68 . In block  70 , the VSS  28  creates a temporary subscriber record and stores it in the VSS  30  and/or HSS  20  of the current network  14 . This may further include providing the subscriber&#39;s IMS profile to the I/S-CSCF  22 , which may include locally-configured iFCs. The iFC triggers third party IMS registration to TAS. Separate iFC sets may be provisioned for each roaming partner. 
         [0025]      FIG. 5  is a simplified flowchart of an exemplary mobile originated method  80  for a visiting subscriber server in an IMS core network. Generally, standard IMS procedures are followed. In blocks  82  and  84 , the UE  10  sends a SIP invite request to the visited P-CSCF with called user identity, which verifies that the public identity in the invite request is currently registered and forwards the request to the inbound roaming I/S-CSCF  22 . iFC execution causes the invite message to be routed to AS/TAS, as shown in block  86 . In block  88 , the TAS then provides originating supplementary and IN (Intelligent Network) services to the UE  10  based on the user profile previously downloaded from the HLR  28 . 
         [0026]      FIG. 6  is a simplified flowchart of an exemplary mobile terminated method  90  for a visiting subscriber server in an IMS core network. In block  92 , standard MAP SRI (Send Routing Information) procedures between GMSC (Gateway Mobile Services Switching Center) and HLR in the HPLMN (Home Public Land Mobile Network) are followed for the mobile terminated call. These procedures include the GMSC sending the HLR a MAP SRI message that contains the MSISDN (Mobile Station International Subscriber Directory Number). The HLR then determines the IMSI from the MSISDN. Because of past UE location updates, the HLR knows the location of the UE, or the serving VLR for the UE. In this instance, the serving VLR is the TAS. In block  94 , the HLR sends a MAP PRN (Provide Roaming Number) message to the TAS. In block  96 , the TAS returns a MSRN (Mobile Station Roaming Number) or IMRN (IP Multimedia Routing Number), which enables the call to be routed to the IMS network where the UE is currently located. The Media Gateway Control Function (MGCF) of the IMS can route the invite message to the inbound roaming I/S-CSCF. The session then follows standard IMS procedures to set up the call. In blocks  98  and  100 , iFC execution or Public Service Identity (PSI) routing routes the invite to the TAS, and the TAS provides terminating supplementary and IN services based on the user profile previously obtained from the HLR. 
         [0027]    Accordingly, an IMS core network is configured to support inbound roaming subscribers of another network operator to derive additional revenue for provision of services. As described above, the Visiting Subscriber Server is configured to support standard 3GPP Cx interface with the I-CSCF and S-CSCF. The VSS is not required to be statically pre-provisioned with subscriber information for the inbound roaming visitors. The VSS is configured to dynamically create temporary subscriber records in response to inbound roaming subscribers accessing the IMS network. The VSS is also configured to retrieve authentication credentials such as AKA vectors from the HLR of the inbound roaming subscriber&#39;s home network for authentication. The VSS is further configured to dynamically derive and create IMS public and private identities for the inbound roaming subscriber based on the MSISDN and IMSI respectively. The VSS is further configured to provide default IMS profile for the inbound roaming subscriber for use during IMS registration. 
         [0028]    The VSS may be a functionality residing in a network node such as the HSS, or it may be an independent network node. The VSS may comprise a server including microprocessor(s), memory, and input and output ports. 
         [0029]    The features of the present invention which are believed to be novel are set forth below with particularity in the appended claims. However, modifications, variations, and changes to the exemplary embodiments described above will be apparent to those skilled in the art, and the system and method described herein thus encompasses such modifications, variations, and changes and are not limited to the specific embodiments described herein.