Abstract:
The present invention discloses a method for implementing simulation services, including the following: an interworking control unit obtains the CS domain network user identifier after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier, puts the obtained user identifier into the SIP message, which is subsequently sent to the IMS network; the IMS network processes the PSTN/ISDN simulation services according to the user identifier. The present invention also discloses a system for implementing simulation service. The present invention makes it unnecessary to extend the existing SIP protocol and to perform signaling interaction between the IMS network and the interworking control unit for obtaining the user identifier, thus simplifying the implementation of the PSTN/ISDN simulation services.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2007/071305, filed on Dec. 21, 2007, which claims priority to Chinese Patent Application No. CN200610172793.0, filed on Dec. 30, 2006, both of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of service processing technologies, and in particular, to a method and a system for implementing the simulation services of the Public Switched Telephone Network/Integrated Service Digital Network (PSTN/ISDN); a method and a control unit for interworking between an IP Multimedia Subsystem (IMS) network and a Circuit Switched (CS) domain network. 
     BACKGROUND OF THE INVENTION 
     With maturity of the packet switching (PS) technologies, the circuit switching (CS)-based traditional telecom networks is developing toward PS-based broadband telecom networks. Using the Session Initiation Protocol (SIP) as a call control signaling of the PS telecom core network is one of the current technical trends. For example, both the International Telecommunications Union-telecom standards part (ITU-T) and the European Telecom Standard Institute (ETSI) currently use the IMS network architecture defined by the 3 rd  Generation Project Partnership (3GPP) as a core network of the Next Generation Network (NGN). 
     In the new PS telecom network, the new PS terminal—SIP terminal gradually replaces the traditional terminal telephone set. In the Telecom and Internet converged Services and Protocols for Advanced Networking (TISPAN) affiliated to the ETSI, the services that are provided to the SIP terminal users in an NGN and have feature same as traditional services are collectively called Public Switched Telephone Network/Integrated Services Digital Network (PSTN/ISDN) simulation services. The TISPAN sets up multiple work items (WIs) to study the simulation services, for example, Originator Identifier Presentation (OIP), and Terminal Identifier Presentation (TIP), and Malicious Call Identification (MCID). 
     In the TISPAN standards, the service logics of the OIP, TIP, and MCID services are implemented on an Application Server (AS). The MCID service and the OIP service need to identify the calling party identifier of a session, and the TIP service needs to identify the called party identifier of a session. When a user is located in an IMS network, the user identifier is carried in the P-Asserted-Identity header field of the SIP message, and the P-CSCF inserts the P-Asserted-Identity header field that carries the user identifier into the SIP message. 
     When the user is located in a CS domain network, the user identifier is transferred through the Calling Party Number parameter and the Connected Number parameter in a Signaling System No. 7 (SS7) message. To obtain the user identifier of the CS domain network from the IMS network, the Media Gateway Control Function (MGCF) unit needs to map the Calling Party Number parameter and the Connected Number parameter to the P-Asserted-Identity header field of the SIP message. However, the CS domain network does not require provision of the user identifier. Therefore, when an SS7 message does not carry the Calling Party Number parameter or the Connected Number parameter, the MGCF fails to obtain the user identifier of the CS domain network user, thus making it impossible to implement the subsequent services. To enable the IMS network to obtain the user identifier of the CS domain network user, at the TISPAN#11ter conference, the DT puts forward, in the 11tTD273 draft, a method for obtaining the calling party identifier from the MCID service.  FIG. 1  shows the process of implementing an MCID service in the prior art, which includes the following steps: 
     Step  101 : When handling the MCID service, the AS of the IMS network detects that the signaling message from the CS domain network does not carry calling party identifier, and hence requests the calling party identifier from the MGCF through an extended SIP message. 
     Step  102 : Upon receiving the request for the calling party identifier, the MGCF sends an identification request (IDR) message to the CS domain network. 
     Step  103 : Upon receiving the IDR message, the CS domain network returns the calling party identifier to the MGCF through an identification response (IRS). 
     Step  104 : Upon receiving the IRS message, the MGCF sends the calling party identifier carried in the message to the AS. The AS performs MCID service processing according to the calling party identifier. 
     This method has the following weaknesses: Firstly, the existing SIP protocol needs to be extended, which makes it more difficult to implement; secondly, the AS needs to perform signaling interaction with the MGCF, which makes it more complex to process network interfaces and AS services. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and a system for implementing simulation services to simplify the implementation of the PSTN/ISDN simulation services. 
     The present invention also provides a method for interworking between the IMS network and the CS domain network, and provides an interworking control unit to simplify the interworking between the IMS network and the CS domain network. 
     The technical solution of the present invention is implemented in the following way. 
     A method for implementing simulation services, including:
         obtaining, by an interworking control unit, the CS domain network user identifier after detecting that the call signaling message from the CS domain network does not carry CS domain network user identifier, and sending the obtained CS domain network user identifier to the IMS network; and   processing, by the IMS network, the PSTN/ISDN simulation services according to the user identifier; and       

     A simulation service implementation system, including:
         a CS domain network, adapted to send a call signaling message to the interworking control unit;   an interworking control unit, adapted to send the obtained CS domain network user identifier to the IMS network after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier; and   an IMS network, adapted to process PSTN/ISDN simulation service according to the CS domain network user identifier sent from the interworking control unit.       

     An interworking control unit, including:
         a default user identifier storage module, adapted to store the default CS domain network user identifiers; and   a user identifier obtaining module, adapted to carry the user identifier read from the default user identifier storage module into a SIP message after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier, wherein the SIP message is subsequently sent to the IMS network.       

     An interworking control unit, including:
         a user identification detecting module, adapted to receive the call signaling message sent by the CS domain network, and send an obtaining indication to a user identifier obtaining module if detecting that the message carries no CS domain network user identifier; and   the user identification obtaining module, adapted to send a request for user identifier to the CS domain network according to the obtaining indication sent by the user identifier detecting module, and put the user identifier sent by the CS domain network into the SIP message, which is subsequently sent to the IMS network.       

     A method for interworking between the IMS network and the CS domain network, including:
         by an interworking control unit, obtaining the CS domain network user identifier after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier, and sending the obtained user identifier to the IMS network.       

     Compared with the prior art, the interworking control unit of the present invention obtains the CS domain network user identifier actively after detecting that the call signaling message from the CS domain network carries no CS domain network user identifier of a call, and sends the user identifier to the IMS network. This makes it unnecessary to extend the existing SIP protocol and perform signalling interworking between the IMS network and the interworking control unit to obtain the user identifier, thus simplifying the interworking between the IMS network and the CS domain network and the implementation of the PSTN/ISDN simulation services. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the time sequence of implementing an MCID service in the prior art; 
         FIG. 2  shows the system structure for implementing the PSTN/ISDN simulation services according to an embodiment of the present invention; 
         FIG. 3  shows the structure of an interworking control unit according to an embodiment of the present invention; 
         FIG. 4  shows the process for implementing a PSTN/ISDN simulation service according to an embodiment of the present invention; 
         FIG. 5  shows the time sequence of implementing an MCID service according to an embodiment of the present invention; 
         FIG. 6  shows the time sequence of implementing an OIP service according to an embodiment of the present invention; and 
         FIG. 7  shows the time sequence of implementing a TIP service according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention is hereinafter described in detail with reference to embodiments and accompanying drawings. 
       FIG. 2  shows the system structure for implementing a PSTN/ISDN simulation service according to an embodiment of the present invention. As shown in  FIG. 2 , the system includes: a CS domain network  21 , an interworking control unit  22 , a session control unit  23 , and a service control unit  24 , wherein the session control unit  23  and the service control unit  24  are located in the IMS network domain. The function of each unit is described below: 
     The CS domain network  21  is adapted to send the call signaling message in the ISDN User Part (ISUP) or the Bearer Independent Call Control (BICC) protocol to the interworking control unit  22 , receive the request for user identifier sent by the interworking control unit  22 , and return a user identifier to the interworking control unit  22 . 
     The interworking control unit  22  is adapted to send a request for user identifier to CS domain network  21  if detecting that the call signaling message received from a CS domain network  21  carries no of the CS domain network user identifier, put the user identifier returned by the CS domain network  21  into the SIP message, and send the SIP message to the session control unit  23 . 
     The interworking control unit  22  may be an MGCF, or an Interworking Border Control Function (IBCF). 
     Alternatively, the interworking control unit  22  is adapted to store the default CS domain network user identifier, and if detecting that the call signaling message received from the CS domain network  21  carries no CS domain network user identifier of a call, put the stored default CS domain network user identifier into a SIP message and send the SIP message to the session control unit  23 . 
     Alternatively, the interworking control unit  22  is adapted to store the default CS domain network user identifier, and after sending a request for user identifier to the CS domain network  21 , if receiving no user identifier returned by the CS domain network  21 , put the stored default CS domain network user identifier into a SIP message and send the SIP message to the session control unit  23 . 
     The session control unit  23  is adapted to receive the SIP message that carries the CS domain network user identifier sent from the interworking control unit  22 , and forward the message to the service control unit  24 . 
     The session control unit  23  may be a CSCF in an IMS network. 
     The service control unit  24  is adapted to process PSTN/ISDN simulation services according to the SIP message that carries the CS domain network user identifier from the session control unit  23 . 
     The service control unit  24  may be an AS in the IMS network. 
       FIG. 3  shows the structure of a session control unit  22  according to an embodiment of the present invention. As shown in  FIG. 3 , the session control unit  22  includes:
         a default user identifier storage module  221 , adapted to store the default CS domain network user identifiers;   a user identification detecting module  222 , adapted to receive the call signaling message sent by the CS domain network  21 , and send an obtaining indication to the user identifier obtaining module  223  if detecting that the message carries no CS domain network user identifier; and   a user identification obtaining module  223 , adapted to send, according to the obtaining indication sent by the user identifier detecting module  222 , a request for user identifier to the CS domain network  21 , and put the CS domain network user identifier returned by the CS domain network  21  into the SIP message, which is subsequently sent to the IMS network.       

     Alternatively, the user identifier obtaining module  223  is adapted to send, according to the obtaining indication sent by the user identifier detecting module  222 , a request for user identifier to the CS domain network  21 , and if no CS domain network user identifier is received from the CS domain network  21 , read the default user identifier from the default user identifier storage module  221 , put the default user identifier into a SIP message, and send the SIP message to the IMS network. 
     Alternatively, the user identification obtaining module  223  is adapted to read, according to the obtaining indication sent by the user identifier detecting module  222 , the default CS domain network user identifier from the default user identifier storage module  221 , put the default CS domain network user identifier into a SIP message, and send the SIP message to the IMS network. 
       FIG. 4  shows the process of implementing a PSTN/ISDN simulation service according to an embodiment of the present invention. As shown in  FIG. 4 , the process includes the following steps. 
     Step  401 : The CS domain network sends a call signaling message to an interworking control unit. 
     Step  402 : Upon receiving the call signaling message, if the interworking control unit detects that the message carries no CS domain network user identifier of the call, the interworking control unit obtains the CS domain network user identifier and puts the user identifier into the SIP message, which is subsequently sent to the IMS network. 
     The CS domain network user identifier may be a calling party identifier or a called party identifier. 
     The interworking control unit may obtain the CS domain network user identifier in the following two modes: 
     Mode 1: The interworking control unit presets a default CS domain network user identifier; if detecting that the call signaling message received from the CS domain network carries no CS domain network user identifier of the call, the interworking control unit puts the default CS domain network user identifier into a SIP message, which is subsequently sent to the IMS network. 
     The default CS domain network user identifier can be set freely, or determined according to the relevant information of each call, for example, according to the network in which the CS domain network user of a current call locates, the information of the circuit occupied by a call, the information of the trunk group that contains the circuit for a call, or the information of the Signaling Point Code (SPC) of the office where the CS domain network user of a current call locates. 
     The interworking control unit may put the default CS domain network user identifier into the SIP message in the following ways: 
     (i) In the header field for carrying the user identifier attribute information in the SIP message, adding a new parameter, which is adapted to indicate that the user identifier carried in this message is a default CS domain network user identifier, for example, adding an enumeration value default in the Privacy header field. 
     (ii) In the header field for carrying the user identifier in the SIP message, adding a new parameter, which is adapted to indicate that the user identifier carried in this message is a default CS domain network user identifier, for example, adding a keyword default in the user identifier P_Asserted_Identity header field. 
     (iii) In the SIP message, adding a header field dedicatedly used for indicating that the user identifier carried in the message is the default CS domain network user identifier. 
     Mode 2: The interworking control unit sends a request for user identifier to the CS domain network if detecting that the call signaling message received from the CS domain network carries no CS domain network user identifier of the call; Upon receiving the message, the CS domain network returns the CS domain network user identifier of the call to the interworking control unit. 
     If the interworking control unit receives no user identifier from the CS domain network, mode 1 may be adopted to obtain the default CS domain network user identifier. 
     Step  403 : Upon receiving the message, the IMS network processes the PSTN/ISDN simulation service according to the CS domain network user identifier carried in the message. 
     The following takes the MCID, OIP and TIP services as examples to describe the present invention. 
       FIG. 5  shows the time sequence diagram of implementing an MCID service according to an embodiment of the present invention. As shown in  FIG. 5 , the process includes the following steps. 
     Step  501 : The user in the CS domain network sends a call request to call the user in an IMS network. Through the Initial Address Message (IAM) in the ISUP protocol, the CS domain network sends a call request to the MGCF that interworks with the IMS network, without putting the calling party identifier in the IAM message. 
     Step  502 : Upon receiving the IAM message, the MGCF detects that the message carries no calling party identifier. 
     Step  503 : The MGCF sends an IDR message to the CS domain network to request the calling party identifier. 
     Step  504 : Upon receiving the IDR message, the CS domain network returns an IRS message to the MGCF. 
     Step  505 : Upon receiving the IRS message, the MGCF judges whether the message carries a calling party identifier. If the message carries a calling party identifier, the process proceeds to step  506 ; otherwise the process skips to step  507 . 
     For certain reasons, the CS domain network may be unable to obtain the calling party identifier, and hence returns an IRS message carrying no calling party identifier to the MGCF. For example, if the call request is sent from office A in the CS domain network through office B to the MGCF, office A knows the calling party identifier from the call request originated by the calling terminal, but the protocol message between office A and office B does not support carrying of a calling party identifier. Therefore, office A is unable to send the calling party identifier to office B. After office B receives an IDR message, because the calling party identifier is unavailable from office A, office B has to return the IRS message without the calling party identifier to the MGCF. 
     Step  506 : The MGCF puts the calling party identifier in the IRS message into the call request (INVITE), which is sent by the S-CSCF to the AS in the IMS network. The process skips to step  408 . 
     Step  507 : The MGCF puts the stored default calling party identifier in the call request (INVITE), which is subsequently sent by the S-CSCF to the AS in the IMS network. 
     The MGCF may set the same default calling party identifier for all calls, or determine the default calling party identifier according to the relevant information of each call, for example, the network in which the calling party locates, the circuit occupied by the call, the trunk circuit for this call, and the SPC of the MGCF. In this embodiment, the MGCF may use the default Telephone Uniform Resource Identifier (TEL URI) tel: +0000-23 as the calling party identifier of the call, where 0000 means that the calling party identifier is the default identifier provided by the MGCF, 23 is the serial number of the trunk circuit for the call; alternatively, the MGCF uses a default SIP URI:DefaultIdCircuit23 @MGCF.com as the calling party identifier of this call, where Circuit23 means that the serial number of the circuit occupied by the call is 23. 
     Step  508 : Upon receiving the call request message, the AS in the IMS network processes the MCID service according to the calling party identifier in the message. 
     In practical applications, if the MGCF detects that the IAM carries no calling party identifier in step  502 , the default calling party identifier can be put into the call request directly and sent to the S-CSCF, without the necessity of sending an IDR message to the CS domain network to obtain the calling party identifier. 
       FIG. 6  shows the time sequence of implementing an OIP service according to an embodiment of the present invention. As shown in  FIG. 6 , the process includes the following steps. 
     Step  601 : The user in the CS domain network originates a call request to call the user in an IMS network. Through the Initial Address Message (IAM) in the ISUP protocol, the CS domain network sends a call request to the MGCF that interworks with the IMS network, without putting the calling party identifier in the IAM message. 
     Step  602 : Upon receiving the IAM message, the MGCF detects that the message carries no calling party identifier. 
     Step  603 : The MGCF sends an information request (INR) message to the CS domain network to request the calling party identifier. 
     Step  604 : Upon receiving the INR message, the CS domain network returns an INF message to the MGCF. 
     Step  605 : Upon receiving the INF message, the MGCF judges whether the message carries a calling party identifier. If the message carries a calling party identifier, the process proceeds to step  606 ; otherwise, the process proceeds to step  607 . 
     Step  606 : The MGCF puts the calling party identifier in the INF message into the call request (INVITE), which is sent by the S-CSCF to the AS in the IMS network. The process skips to step  608 . 
     Step  607 : The MGCF puts the stored default calling party identifier in the call request (INVITE), which is subsequently sent by the S-CSCF to the AS in the IMS network. 
     Step  608 : Upon receiving the call request message, the AS in the IMS network processes the OIP service according to the calling party identifier in the message. 
     In practical applications, if the MGCF detects that the IAM carries no calling party identifier in step  602 , the default calling party identifier can be put into the call request directly and sent to the S-CSCF, without the necessity of sending an INR message to the CS domain network to obtain the calling party identifier. 
       FIG. 7  shows the time sequence of implementing a TIP service according to an embodiment of the present invention. As shown in  FIG. 7 , the process includes the following steps. 
     Step  701 : The user in the IMS network sends a call request to call the user in a CS network. The IMS network sends a call request (INVITE) to the MGCF that interworks with the CS domain network. 
     Step  702 : Upon receiving the call request message, the MGCF sends an IAM message to the CS domain network. 
     The IAM message may carry an indication that requests the called party identifier. 
     Step  703 : Upon receiving the IAM message, the CS domain network returns an answer (ANM) message to the MGCF. 
     Step  704 : Upon receiving the ANM message, the MGCF detects that the message carries no called party identifier. 
     Step  705 : The MGCF puts the stored default called party identifier in the  200  OK message, which is subsequently sent by the S-CSCF to the AS in the IMS network. 
     Step  706 : Upon receiving the  200  OK message, the AS in the IMS network processes the TIP service according to the called party identifier in the message. 
     The preceding embodiments are exemplary embodiments of the present invention only and not intended to limit the present invention. Any modification, equivalent substitution or improvement without departing from the spirit and principle of the present invention should be covered in the scope of protection of the present invention.