Patent Publication Number: US-8989178-B2

Title: System and method for indicating circuit switched access at IMS registration

Description:
RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 12/594,182 filed Feb. 24, 2010, which is a 371 of International Application No. PCT/IB2007/000843, filed Mar. 30, 2007, the disclosures of which are fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to IP Multimedia Subsystem (IMS). More particularly, and not by way of limitation, the present invention is directed to a system and method for assisting in the IMS user registration process. 
     BACKGROUND 
     The following is a list of acronyms used in the body of the specification and their definitions, which shall apply throughout the specification unless otherwise noted. 
     Acronyms 
     3GPP: 3rd Generation Partnership Project 
     ADS: Access Domain Selection 
     AS: Application Server 
     CAMEL: Customized Application for Mobile network Enhanced Logic 
     CDR: Call Data Record 
     CS: Circuit Switch 
     CSCF: Call Session Control Function 
     CSI: Combination of CS and IMS service 
     IA: IMS Adapter 
     ICCF: IMS Circuit Switch Control Function 
     ICCP: IMS Circuit Switch Control Protocol 
     ICS: IMS Centralized Services 
     IMPI: IP Multimedia Private Identity 
     IMS: IP Multimedia Subsystem 
     IMSI: International Mobile Subscriber Identity 
     IP-CAN: IP Connectivity Access Network 
     ISC: IP multimedia Subsystem Control 
     ISUP: ISDN User Part 
     MAP: Mobile Application Part 
     MGCF: Media Gateway Control Function 
     PS: Packet Switched 
     P-CSCF Proxy Call Session Control Function 
     S-CSCF Serving Call Session Control Function 
     SIP Session Initiation Protocol 
     TAS: Telephony Application Server 
     UE: User Equipment 
     URL: Uniform Resource Locator 
     USSD: Unstructured Supplementary Service Data 
     VCC: Voice Call Continuity 
     WCDMA: Wideband Code Division Multiple Access 
       FIG. 1  depicts a high-level block diagram of ICS architecture  100 . IMS Centralized Services (ICS) is a proposed work item in Third Generation Partnership Project (3GPP) to make possible IMS services over many types of access networks, such as Circuit Switched (CS) network  102 . Service implementation resides in IMS  110  and CS network  102  is used as an access to the services in IMS  110 . 
     As compared to 3GPP Release 7, Voice Call Continuity (VCC) architecture, IMS CS Control Function (ICCF)  106  is introduced to allow signaling not supported over CS signaling (e.g., ISUP) such as IMS registration, mid-call signaling, additional information for call set-up signaling (e.g., SIP URL), to emulate an NMS terminal towards the IMS. Unstructured Supplementary Service Data (USSD) can be used to transport this additional signaling called ICCP (IMS CS Control)  104  in CS network. 
     In 3GPP Release 7 VCC, the VCC user is not IMS registered at CS access and Telephony Application Server (TAS)  108  has to implement additional mechanisms to provide IMS services to a user. A possible solution, in 3GPP Release 8, it is proposed to support IMS registration from UE  101  using ICCP so that TAS  108  can be informed from S-CSCF by a third party registration procedure that a user is IMS registered. The Serving CSCF is a call session control function for handling user equipment registration and routing for an IP multimedia subsystem. Another CSCF, the Proxy-CSC, is the first point of contact for user equipment and handles security, verification and policy decisions. Currently there is no procedure that informs the IMS whether a user is registered at CS access or at PS access (this is because there was previously no IMS registration for a CS access). IMS can only know that the user is registered at one or more radio accesses, where it is assumed that all accesses are packet-accesses. Packet Switched (PS) access has always been assumed in IMS. 
     Because of the assumption that the access is always PS access, there are situations that cannot be addressed by the IMS third party registration mechanism up to 3GPP Release 7. For instance, an operator may want to implement local policy in S-CSCF contact address selection to prefer CS access rather than PS access; or vice versa. An operator may want to differentiate charging for CS access and PS access and indicate that difference in IMS CDRs. Also, an operator may want to differentiate the TAS behavior if a user is registered at CS access or PS access (e.g. Call forwarding Video to Video mail box if a user is registered at CS access where video cannot be supported). 
     It would be advantageous to have a system and method for identifying whether a user is registered at CS or PS access that overcomes the disadvantages of the prior art. The present invention provides such a system and method. 
     SUMMARY OF THE INVENTION 
     The present invention provides a change in SIP interface, e.g., among ICCF, CSCF and AS, to support indication of CS access in P-Access-Network-Information header. Impacted nodes are ICCF, S-CSCF and AS. The indication can be used by S-CSCF or AS for different purposes such as routing decision, charging, and presence info. 
     Thus, in one aspect, the present invention is directed to a method for registering user equipment (UE) in an IP multimedia subsystem (IMS), by sending a registration request to a Serving Call Session Control Function (S-CSCF), wherein the registration request includes a header containing information about access type of the user and contacts related to the access type. The registration request is forwarded to an IMS associated application server which responds to the ICCF. The S-CSCF utilizes the inserted registration request header to implement access rules according to operator or user preference, wherein the header included in the registration request is a P-Access Network-Information header which includes contacts related to Circuit Switched access. 
     Contact addresses related to Circuit Switched access in the header are arranged in order of use before a normal, Packet Switched access contact and ordering rules regarding contact handling, related to the access type, are based on local policy in the S-CSCF. The local policy in the S-CSCF may be dependent on time of day or according to a subscriber profile. 
     In another aspect, the present invention is directed to a system for registering user equipment (UE) in an IP multimedia subsystem (IMS), wherein the system comprises means for sending a registration request to a Serving Call Session Control Function (S-CSCE) and the registration request includes a header containing information about access type of the user and contacts related to the access type. The system includes means for forwarding the registration request to an IMS associated application server and means for sending a registration response to the ICCF. 
     There are means included in the S-CSCF for utilizing the registration request header to implement access rules according to operator or user preference and the header that is included in the registration request is a P-Access Network-Information header that includes contacts related to Circuit Switched access. 
     Contacts related to Circuit Switched access in the header can be arranged in order before a normal, Packet Switched access contact and the ordering rules, regarding contact handling related to the access type on local policy in the S-CSCF, the local policy in the S-CSCF being dependent on time of day or according to a subscriber profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following section, the invention will be described with reference to exemplary embodiments illustrated in the figures, in which: 
         FIG. 1  depicts a high-level block diagram of ICS architecture; 
         FIG. 2  illustrates a high-level signaling diagram of Circuit Switched Access at registration in accordance with an embodiment of the present invention; and 
         FIGS. 3   a ,  3   b  and  3   c  depict three situations in which a registered device identified in a S-CSCF according to embodiments of the present invention; 
         FIGS. 4   a - 4   d  illustrate situations in which ordering in the S-CSCF is changed in accordance with an embodiment of the present invention; 
         FIGS. 5   a - 5   d  depict situations wherein different forking actions may be taken according to an embodiment of the present invention; 
         FIGS. 6   a - 6   f  illustrate situations regarding different sequential ringing actions according to an embodiment of the present invention; and 
         FIG. 7  depicts Circuit Switched access indication to a presence server according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. 
     A parameter associated with IMS, “P-Access-Network-Information” already exists to deliver access specific network information, but no additional information indicating access type (CS or PS) is currently included in this parameter. Prior to the introduction of ICS, PS access was the default case. The P-Access-Network-Information header is described below for reference: 
     
       
         
           
               
             
               
                   
               
             
            
               
                    access-type = “IEEE-802.11” / “IEEE-802.11a” / 
               
               
                 “IEEE-802.11b” / “IEEE-802.11g” / “3GPP-GERAN” / 
               
               
                 “3GPP-UTRAN-FDD” / “3GPP-UTRAN-TDD” / “ADSL” / 
               
               
                 “ADSL2” / “ADSL2+” / “RADSL” / “SDSL” / 
               
               
                 “HDSL” / “HDSL2” / “G.SHDSL” / “VDSL” / 
               
               
                 “IDSL” / “3GPP2-IX” / “3GPP2-IX-HRPD” / 
               
               
                 “DOCSIS” / token 
               
               
                    access-info = cgi-3gpp / utran-cell-id-3gpp / dsl-location / i-wlan- 
               
               
                 node-id / ci-3gpp2 / extension-access-info 
               
               
                    extension-access-info = gen-value 
               
               
                    cgi-3gpp = “cgi-3gpp” EQUAL (token / quoted-string) 
               
               
                    utran-cell-id-3gpp = “utran-cell-id-3gpp” EQUAL (token / 
               
               
                    quoted-string) 
               
               
                    i-wlan-node-id = “i-wlan-node-id” EQUAL (token / quoted-string) 
               
               
                    dsl-location = “dsl-location” EQUAL (token / quoted-string) 
               
               
                    ci-3gpp2 = “ci-3gpp2” EQUAL (token / quoted-string) 
               
               
                   
               
            
           
         
       
     
       FIG. 2  illustrates a high-level signaling diagram of Circuit Switched Access at registration in accordance with an embodiment of the present invention. P-Access-Network-Information header is extended in the present invention to indicate access type as CS and is inserted by ICCF into an ICCP registration request and delivered to S-CSCF and an Application Server (AS). The Application Server can be Telephony Application Server or Voice Call Continuity AS or any other AS (e.g., Presence Server) which uses registration status to execute its application on top of IP Multimedia Subsystem Control (ISC) interface. The S-CSCF can also use P-Access-Network Information to implement rules following operator or user preference to put contacts related to CS access in different order than PS access. 
       FIGS. 3   a ,  3   b  and  3   c  depict three situations in which a registered device is identified in a S-CSCF according to embodiments of the present invention. Differentiation between CS and PS UE devices is accomplished utilizing information included in the registration message provided by ICCF using ICCP.  FIG. 3   a  depicts utilizing a “Device ID” from UE during registration both in CS and in PS. This is a new parameter in ICCP registration request and in a SIP REGISTER message and S-CSCF needs to store the “Device ID” information with contact IP address. For example, if two devices are registered, one UE with CS and PS access, and another UE being a PC with only PS access, the information stored in S-CSCF appears as: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Public User ID --- Contact IP1 --- CS access --- Device ID1 
               
               
                   
                         +-- Contact IP2 --- PS access --- Device ID1 
               
               
                   
                         +-- Contact IP3 --- PS access --- Device ID2 
               
               
                   
                   
               
               
                   
                 Note 1 
               
               
                   
                 IP1 is ICCF IP address in CS access case. 
               
            
           
         
       
     
       FIG. 3   b  illustrates including at least one “alternative contact” from UE during CS registration. In an ICCP registration request and REGISTER message, S-CSCF needs to store the “alternative contact” information with contact IP address for CS access. S-CSCF can identify that two registrations belong to the same device matching contact address and alternative contact address. For example, if case 2 devices are registered, one UE with CS and PS access, and another UE being a PC with only PS access, the information stored in S-CSCF appears as: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Public User ID --- Contact IP1 --- CS access --- Alt contact IP2 
               
               
                   
                         +-- Contact IP2 --- PS access 
               
               
                   
                         +-- Contact IP3 --- PS access 
               
               
                   
                   
               
               
                   
                 Note 
               
               
                   
                 IP1 is ICCF IP address in CS access case. 
               
            
           
         
       
     
       FIG. 3   c  depicts using IP Multimedia Private Identity (IMPI) to identify the device. IMPI can be derived from IMSI delivered in ICCP registration request (MAP USSD message), and can be populated in an existing Authorization header in a REGISTER message. S-CSCF needs to store the IMPI information with contact IP address to be used for routing decision. For example, if two devices are registered, one UE with CS and PS access, and another UE as being a PC with only PS access, the information stored in S-CSCF looks as follows: 
     
       
         
           
               
               
             
               
                   
                   
               
             
            
               
                   
                 Public User ID --- Contact IP1 --- CS access --- IMPI1 
               
               
                   
                         +-- Contact IP2 --- PS access --- IMPI1 
               
               
                   
                         +-- Contact IP3 --- PS access --- IMPI2 
               
               
                   
                   
               
               
                   
                 Note 1 
               
               
                   
                 IP1 is ICCF IP address in CS access case. 
               
               
                   
                 Note 2 
               
               
                   
                 IMPI1 is derived from IMSI and IMPI2 is stored in IMSI attached to PC. 
               
            
           
         
       
     
       FIGS. 4   a - 4   d  illustrate situations in which ordering in the S-CSCF is changed in accordance with an embodiment of the present invention. The S-CSCF can also use P-Access-Network Information to implement rules following operator or user preference to put contacts related to CS access in different order than a typical PS access. 
     Currently, contact handling is only based on q-value from the user. The q parameter is used to indicate priority value of the contacts for routing from a user. The present invention provides for an ordering rule that can be based on local policy in S-CSCF and may be different, e.g., dependent on time of day or per subscriber. Possible orderings in the S-CSCF may include: 
     Try CS access contact first and then try PS access if no reply ( FIG. 4   a ); 
     Try PS access contact first and then try CS access if no reply ( FIG. 4   b ); 
     Try CS access contact only if both CS and PS access contacts are registered (if only one contact is registered, try the registered contact) ( FIG. 4   c ); and alternatively, 
     Try PS access contact only if both CS and PS access contacts are registered of only one contact is registered, try the registered contact) ( FIG. 4   d ). These options would expand contact handling in the S-CSCF which is only based on q-value from the user today. 
       FIGS. 5   a - 5   d  depict situations wherein different forking actions may be taken according to an embodiment of the present invention. The S-CSCF can also use the P-Access-Network-Information to implement rules to suppress forking to contacts for the same device registered over multiple accesses. The forking rule may be based on local policy in S-CSCF and may be different, e.g., dependent an time of day. Possible forking rules include: 
     Fork to only PS access contact if a user is registered at both CS and PS access ( FIG. 5   a ); 
     Fork to only CS access contact if a user is registered at both CS and PS access ( FIG. 5   b ). 
     Fork to PS access contact first, then to CS contact ( FIG. 5   c ) and 
     Fork to CS access contact first, then fork to PS contact ( FIG. 5   d ). 
     The rule can be also combined with sequential ringing so that: 
     Fork to only PS access contact if a user is registered at both CS and PS access. If none of the forked devices reply, try CS access contact and 
     Fork to only CS access contact if a user is registered at both CS and PS access. If none of the forked devices reply, try PS access contact. 
     The forking rule can be based on local policy in S-CSCF and may be different e.g. dependent on time of day. 
       FIGS. 6   a - 6   f  illustrate situations regarding different sequential ringing actions according to an embodiment of the present invention. The S-CSCF can use the P-Access-Network-Information to sequentially ring the contacts in a way that contacts related to the same device but to different accesses are tried in sequence before (or after) trying to ring contacts pointing to other devices. In other words, possible sequential ringing rules include: 
     1) While sequentially ringing different devices, try PS access contact first if a user is registered at both CS and PS access. If no reply:
         Try CS access before trying another device ( FIG. 6   a );   Try CS access contact after all sequential ringing to other devices are not responded to ( FIG. 6   b ); and       

     do not include CS access contact ( FIG. 6   c ); 
     2) While sequentially ringing different devices, try CS access contact first if a user is registered at both CS and PS access. If no reply: 
     Try PS access before trying another device ( FIG. 6   d ); 
     Try PS access contact after no response to all sequential ringing to other devices ( FIG. 6   e ); and 
     do not include P access contact ( FIG. 6   f ). 
     The sequential ringing rule can be based on local policy in S-CSCF and may be different, e.g., depending on time of day. 
     These parameters can be included in P-Access-Network-Information or can be included as a new SIP header parameter. The AS can use the contact information to differentiate between CS access and PS access for Access Domain Selection (ADS). 
     In VCC 3GPP Release 7, the VCC application server implements ADS. When ADS selects PS access, the call is routed to the registered contact in PS access. When ADS selects CS access, since S-CSCF does not have any registered contact at CS access, ADS re-targets a call using a suitable routing number to be able to route to CS access (called CS routing number), to bypass the contact handling in the S-CSCF. VCC AS may know the PS registration status using 3rd party registration mechanism when user is registered at PS access but needs to implement specific non-IMS mechanism to know that a user is registered at CS access. IMS 3rd party registration may also be used to determine the registration status at CS access, which would simplify the ADS implementation. 
     The AS and S-CSCF can issue a CDR including P-Access network-Information so that an operator can differentiate the charging scheme for a communication over PS access and a communication over CS access. P-Access-network-Information can be also included in the INVITE request when the session is established from ICCF (not only REGISTER message when user registers at CS access) in order to indicate that the communication is over CS access. 
       FIG. 7  depicts Circuit Switched access indication to a presence server according to an embodiment of the present invention. A presence server, being an SIP AS can also receive P-Access-Network-Information during third party registration procedures to determine whether the user is in PS access or in CS access and can provide better information to watchers. A “Watcher” in this context is a user subscribed to presence information of an ICS user and “watches” the presence status of an ICS user. A watcher uses the presence status to decide which access should be used to initiate multimedia communication s that if the user is registered at PS access, the watcher can initiated multimedia call over PS access (e.g., voice and video over PS access). Such a watcher may reside in a UE or in a network node. 
     As will be recognized by those skilled in the art, the innovative concepts described in the present application can be modified and varied over a wide range of applications. Accordingly, the scope of patented subject matter should not be limited to any of the specific exemplary teachings discussed above, but is instead defined by the following claims.