Abstract:
An exemplary method provides access to call origination features contained in an internet protocol multimedia subsystem (IMS) for a subscriber of the IMS who originates a call request from customer premises equipment (CPE) outside of the IMS. The call request is received at a public service identity (PSI) server in the IMS with a phone number to which the call request is routed. An IMS internal desk number is retrieved based on the number of the outside CPE. A first modified call request is transmitted from the PSI server to a telephony application server (TAS) identifying the IMS internal desk number as a request universal resource identity (RURI). Call origination treatment as specified by the subscriber is performed by the TAS. The first modified call request is processed by the TAS to form a second modified call request in which the RURI is a number of a destination party and a P-asserted identity (PAID) is the IMS internal desk number such that the second modified call request appears as if it was initiated from a phone within the IMS. The second modified call request is transmitted to a node in the IMS for further processing and ultimately termination at the destination party.

Description:
BACKGROUND 
     This invention relates to telephone networks, and more specifically to call origination processing. 
     Telephone subscribers are provided with a variety of services, some of which are provided as optional services requiring an additional payment by a subscriber electing such services. Plain old telephone service (POTS) subscribers of the public switched telephone network (PSTN) have access to a variety of standard features such as three-way conference calling, speed dialing, etc. These features are provided by the PSTN switch that supports call origination services its subscribers, i.e. the switch to which the subscriber&#39;s telephone lines are connected. The services are normally associated with a particular telephone line termination on the switch. These services are provided to the subscriber only on the predetermined telephone line of the subscriber. 
     For groups of devices with a common affiliation, e.g. multiple phones belonging to a specific subscriber like a desk phone, cellular phone, and/or softphone, it is many times desirable to provide a common user experience for a call originating from (or terminating to) that device. Normally, such devices are supported by different networks despite the fact that they are owned by the same subscriber. Because of this fact, user experience for the subscriber can vary based on: 1. the implementation of services in the different networks 2. The way services are provisioned in the different networks. Each network may support its own call origination features such as a speed dialing list, extension-only dialing capabilities, etc. Normally such call origination features are separate to the different networks. That is, a subscriber that initiates a call from a telephone outside of the network where the desk phone is subscribed, e.g. a general PSTN supported telephone or a cellular telephone, will not be able to utilize the same call origination features made available to that subscriber&#39;s desk phone. Therefore, a need exists to provide access to call origination features provided to a subscriber when the subscriber initiates calls from any one of his/her devices. 
     SUMMARY 
     It is an object of the present invention to satisfy this need. 
     An exemplary method provides access to call origination features contained in an internet protocol multimedia subsystem (IMS) for a subscriber of the IMS who originates a call request from customer premises equipment (CPE) either inside or outside of the IMS. The call request is received at a public service identity (PSI) server in the IMS with a phone number to which the call request is routed. An IMS internal desk number for the subscriber is retrieved based on the calling party number of the outside CPE. A first modified call request is transmitted from the PSI server to a telephony application server (TAS) identifying the IMS internal desk number as a request universal resource identity (RURI). Call origination treatment as specified by the subscriber is performed by the TAS. The first modified call request is processed by the TAS to form a second modified call request in which the RURI is a number of a destination party and a P-asserted identity (PAID) is the IMS internal desk number such that the second modified call request appears as if it was initiated from a phone (the subscriber&#39;s desk number) within the IMS. The second modified call request is transmitted to a node in the IMS for further processing and ultimately termination at the destination party. 
     An illustrative apparatus is used to implement the above exemplary method. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Features of exemplary implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
         FIG. 1  is a block diagram of a telephony system in accordance with an embodiment of the present invention. 
         FIG. 2  illustrates an exemplary provisioning in accordance with an embodiment of the present invention. 
         FIG. 3  is a signal flow diagram in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a telephony system that includes a subscriber&#39;s desk phone that may reside in a private telephone subsystem, an Internet protocol multimedia subsystem (IMS),  10  and a public telephone network  12 . Subscribers of IMS  10  are provided with selectable call origination features that are unique to their desk phone and the private telephone subsystem, e.g. dialing of internal desk phone numbers by only entering a 3 or 4 digit extension number, etc. Prior to the present invention, its subscribers could access the call origination features while at a telephone set, but were unable to access a call origination feature of this specific desk number and the private telephone system from a telephone set external to the IMS. It is a general objective in accordance with the present invention to provide to subscribers of the IMS network with access to call origination features provided by this network when the subscriber initiates a call from a telephone set external to the this network, in particular from a telephone set in the PSTN. 
     The illustrative public telephone network  12  includes a cellular telephone  14  that is supported by radio access node (RAN)  16  and mobile switching center (MSC)  18  that is connected to the private switched telephone network (PSTN)  20 . Customer premises equipment (CPE), e.g. a POTS telephone set,  22  is supported by a central office switch  24  that is connected to the PSTN  20 . Cellular telephone  14  and the CPE  22  merely represent a variety of communication devices that can be used in the public telephone network. 
     In describing the IMS  10 , elements may be referred to as supporting identified functionality. It will be understood by those skilled in the art that this functionality is implemented by a corresponding apparatus or server. A media gateway control function (MGCF)  26  is coupled to the PSTN  20  and to a session manager  28  that includes an interrogating-call session control function (I-CSCF)  30 , a serving call session control function (S-CSCF)  32  and a proxy call session control function (P-CSCF)  34 . The session manager  28  is coupled to a home subscriber server (HSS)  36  which provides service profiles and manages authentication and registration status of users. The session manager  28  is also supported by a public service identity (PSI) server  38  and a telephony application server (TAS)  40 . Telephone sets  42 ,  44  and  46  are coupled to the session manager  28  and have corresponding subscribers registered with IMS  10 . These telephone sets are internal to IMS  10  and hence subscribers using these telephone sets have access to call origination features supported by the IMS  10 . 
       FIG. 2  illustrates an exemplary record  50  that can be accessed by the PSI server  38  where the record is associated with a directory number (DN), i.e. the desk number, of a subscriber of IMS  10 . The record provides provisioning internal to IMS  10  that enables a subscriber to identify one or more directory numbers of CPE external to the IMS  10  from which a subscriber of the IMS  10  can gain access to the IMS  10  in a manner that permits access to call origination features of the subscriber&#39;s desk number on the IMS  10 . 
     The illustrative record  50  may include fields or entries  52 - 60  that contain corresponding information and/or data. Field  52  contains a PSI directory number that functions as a destination telephone number for PSI server  38  for calls initiated outside of the IMS  10 . Field  54  contains the public user identification (PUID) of the subscriber&#39;s desk number, i.e. the publicly known DN for calls terminating to the subscriber in the IMS  10 . Field  56  contains a personal identification number (PIN) of the subject subscriber that may in the example consist of 4-10 digits that can be selected by the subscriber. Field  58  contains a function selectable by the subscriber that determines whether a call origination from an extension dialing the desk number should be treated as an intercom call or as an attempt to access voice mail. Field  60  may include a plurality of entries, each associated with a different DN of CPE external to the IMS from which a subscriber may desire to gain access to the IMS  10  in accordance with an embodiment of the present invention. In field  60 , “extension xx (DN)”, the DN is directory number of a CPE outside of the IMS, e.g. phones  14  or  22 ; “alert (Y/N)” provides an election of whether the external DN is alerted upon a terminating call to the associated desk number; “PIN required (Y/N)” specifies whether the entry of the defined PIN must be entered in order to gain access from the external extension DN; “bridge (Y/N)” specifies whether a user at the associated directory number DN will be allowed to bridge into an existing call utilizing the desk phone or other extensions. 
     The following table defines several abbreviations used herein and in the figures. 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Abbreviation 
                 Definition 
               
               
                   
                   
               
             
             
               
                   
                 CDPN 
                 Called Party Number 
               
               
                   
                 CGPN 
                 Calling Party Number 
               
               
                   
                 CPE 
                 Customer Premises Equipment 
               
               
                   
                 DIV 
                 Diversion Header 
               
               
                   
                 IMS 
                 Internet protocol Multimedia Subsystem 
               
               
                   
                 I-CSCF 
                 Interrogating Call Session Control Function 
               
               
                   
                 MGCF 
                 Media Gateway Control Function 
               
               
                   
                 OCN 
                 Original Called party number 
               
               
                   
                 PAID 
                 P-Asserted-Identity 
               
               
                   
                 PBX 
                 Private Branch Exchange 
               
               
                   
                 PCN 
                 P-Called-Party-Identity 
               
               
                   
                 P-CSCF 
                 Proxy Call Session Control Function 
               
               
                   
                 PIN 
                 Personal Identification Number 
               
               
                   
                 POTS 
                 Plain Old Telephone Service 
               
               
                   
                 PSI 
                 Public Service Identity 
               
               
                   
                 PSTN 
                 Public Switched Telephone Network 
               
               
                   
                 PUID 
                 Public User Identification 
               
               
                   
                 RURI 
                 Request Universal Resource Identity 
               
               
                   
                 S-CSCF 
                 Serving Call Session Control Function 
               
               
                   
                 TAS 
                 Telephony Application Server 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 3  is a signal flow diagram of an illustrative embodiment of the present invention. In this embodiment a subscriber of IMS  10 , having previously completed provisioning such as shown in  FIG. 2  for external DNs, initiates a call from an external telephone having one of the provisioned external DNs. The subscriber desires to use call origination features of IMS  10 , e.g. extension only dialing, even though he is initiating the call from cellular handset  14  that has its DN entered as extension  1  of field  60 . 
     In this example the cellular system that supports handset  14  includes a “hot line feature”, i.e. where an originating call from handset  14  is routed to a predetermined telephone number no matter what destination telephone number is manually entered by the user. In this case the hot line number to which the call is routed is the phone number for PSI server  38 . A call request made from a service with a hot line feature is placed to the predetermined destination telephone number, but also contains the number entered by the subscriber and the calling party&#39;s phone number. 
     Referring to  FIG. 3 , the IMS subscriber initiates the illustrative call request from cellular handset  14 . The call request is routed by RAN  16 , MSC  18 , and PSTN  20  to the MGCF  26 . In order to facilitate understanding of the call flow, the nodes are numbered to reflect the call sequence. However, these elements correspond to the same named physical elements shown in the IMS of  FIG. 1 . The call request is received by MGCF  50  as an integrated services digital network user part (ISUP) initial address message (IAM). This message contains the calling party number (CGPN) of the cellular handset  14 , i.e. mobile directory number (M-DN), the called party number (CDPN) of the phone number of the PSI server, and the original called party number (OCN) entered by the subscriber of the actual destination party (B-DN). 
     The MGCF  50  generates a corresponding SIP INVITE call request message that is transmitted to the I-CSCF  52 . In this message, the M-DN is identified as the P-Asserted Identity (PAID), the PSI number identified as the Request Universal Resource Identity (RURI), and the B-DN identified as the P-Called-Party identity (PCN) or the Diversion header (DIV). The I-CSCF  52  queries the HSS  36  based on the identified RURI and determines the associated PSI server  54  (PSI server  38  in  FIG. 1 ) to which the call request will be routed. The PSI server queries an associated database based on the received M-DN to identify the corresponding subscriber&#39;s desk number, i.e. the number/line of the IMS subscriber corresponding to the call originating subscriber. The server will also prompt for and validate a PIN from the originating subscriber, if a PIN is required in accordance with the corresponding record. 
     The PSI server  54  transmits a further call request message to I-CSCF  56 . In this message the PAID remains the M-DN and the PCN continues to identify the B-DN, but the RURI is identified as the desk DN and an access is identified by the extension number associated with the M-DN. The I-CSCF  56  in turn routes the message to S-CSCF  58  which in turn routes it to TAS  60 . 
     One of the tasks of the TAS  60  is to effectively change in the call request from an incoming call termination to an outgoing call origination. This is accomplished by transmitting a call message to the S-CSCF  62  in which: PAID=desk DN; RURI=B-DN; DIV=desk DN; with a Route header identified as “orig”, i.e. a call origination. Also the TAS  60  will prompt the originating subscriber to manually enter the B-DN if the B-DN is not contained in part of the message received by the TAS. Although the B-DN is received as part of the call request message by the TAS  60  in this embodiment, the B-DN may not be received as part of the call request message by the TAS  60  as will be explained later with regard to another embodiment. 
     The S-CSCF  62  determines how the call to B-DN should be routed. B-DN could identify another subscriber within the same IMS, a subscriber within another IMS or a PSTN user. In this example, that B-DN identifies a subscriber on the same IMS and as such, the S-CSCF  62  transmits the call origination message request to I-CSCF  64  which in turn routes the request to the S-CSCF  66  and then to TAS  68 . The same TAS  40  may serve as TAS  60  and TAS  68 . Alternatively, TAS  60  and TAS  68  may be implemented by two separate servers in the IMS (not shown in  FIG. 1 ). The TAS  68  generates a call origination request message transmitted to S-CSCF  70  in which: PAID=desk DN; RURI=B-DN; DIV=desk DN. Call path routing proceeds with this call origination request message being transmitted from S-CSCF  70  to P-CSCF  72  that functions as a proxy causing the call origination request to be normally processed concluding in a termination at the CPE with the B-DN showing the call origination having come from the desk DN. The CPE with the B-DN may reside internal or external of the IMS. 
     Because the TAS  60  effectively switches the incoming call termination of cellular handset  14  into a call origination from the corresponding desk DN, the TAS can also provide any call origination features and services that would have been supplied to the subscriber had the call been actually originated from the CPE associated with the desk DN. Thus the IMS subscriber is provided access to call origination features and services even when originating calls from a CPE outside of the IMS. 
     In an alternative embodiment a subscriber of the IMS desires to make use of call origination features supported by the IMS while initiating the call from a CPE external to the IMS. In this example the subscriber initiates a call from CPE  22  which is supported by telecommunication infrastructure that does not support a hot line feature. In this scenario the subscriber dials the phone number associated with the PSI server, wherein the call was routed by the central office switch  24  and PSTN  20  to the IMS  10  containing PSI server  38 . As explained in  FIG. 3 , the PSI server  54  locates the desk number in the record shown in  FIG. 2  associated with the previously provisioned external extension from which the subscriber is calling. The call proceeds to TAS  60  as explained for the above embodiment. Because a final destination number (B-DN) will not be contained in the call request message in this embodiment, the TAS  60  will prompt the originating subscriber to enter the B-DN and receive the B-DN as entered from the subscriber. Now that the actual destination number has been obtained by the TAS  60 , the call request is routed and proceeds as explained for the above embodiment. Thus, the subscriber can access call origination features and services provided by the IMS  10  even when originating an external call from a CPE in a system that does not support a hot line feature. 
     Although exemplary implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention. For example, the functions performed by one or more of the IMS elements can be integrated into another element so that the latter is capable performing all the associated functions. The described steps and signal flows may be performed in a different order, combined together to form fewer steps or signal flows, and/or certain steps or signal flows may be omitted depending on the capabilities of the supporting infrastructure. 
     The scope of the invention is defined in the following claims.