Handling a registration timer to provide service continuity in IMS

Abstract

The invention relates to a method for providing service continuity with respect to a registration of a mobile terminal, UE, at a control server of an IP Multimedia Subsystem, IMS, network, while a CS-communication session between the UE and a switching server, MSC, of a circuit-switched, CS, network is established. The control server comprises a registration timer which is used for initiating a termination of the registration of the UE at the IMS network, when the registration timer expires, wherein the control server updates the registration timer in dependence of a control information received from the MSC. The invention further relates to a MSC providing such service.

1 . A method of providing service continuity with respect to a registration of a mobile terminal (UE) at a control server of an IP Multimedia Subsystem (IMS) network, while a CS-communication session between the UE and a switching server (MSC) of a circuit-switched (CS) network is established, the method comprising:
 the control server utilizing a registration timer for initiating a termination of the registration of the UE at the IMS network, when the registration timer expires, and   the control server updating the registration timer independent of a control information received from the MSC.   
     
     
         2 . The method according to  claim 1 , wherein the control information is sent to the control server before the registration timer expires. 
     
     
         3 . The method according to  claim 1 , wherein the control information comprises an information that the UE cannot update the registration timer. 
     
     
         4 . The method according to  claim 3 , wherein the control information additionally comprises information about a user identity of the UE or an equipment identity of the UE. 
     
     
         5 . The method according to  claim 3 , wherein the control server, after receiving the control information from the MSC, updates the registration timer prior to the registration timer expiring. 
     
     
         6 . The method according to  claim 5 , wherein the MSC triggers the control server to terminate updating the registration timer in the control server after the communication session between the UE and the MSC is released. 
     
     
         7 . The method according to  claim 1 , wherein the MSC initiates the update of the registration timer in the control server by
 requesting the registration timer value from the control server of the IMS network and,   after receiving the registration timer value and detecting that the registration timer is near expiration, triggering the control server of the IMS network to update the registration timer.   
     
     
         8 . The method according to  claim 7 , wherein the request of the registration timer value also comprises the user identity of the UE or the equipment identity of the UE. 
     
     
         9 . The method according to  claim 1 , wherein the control server, after updating the registration timer, sends a notification message to a serving node of the IMS network to trigger an update of an additional registration timer in the serving node. 
     
     
         10 . The method according to  claim 8 , wherein the serving node is a Server Call Session Control Function (S-CSCF) server. 
     
     
         11 . The method according to  claim 1 , wherein the control server of the IMS is a Proxy Call Session Control Function (P-CSCF) server. 
     
     
         12 . The method according to  claim 1 , wherein the MSC receives the address of the control server of the IMS network in response to the registration of the UE at the control server of the IMS network. 
     
     
         13 . The method according to  claim 1 , wherein the MSC receives the address of the control server of the IMS network, when the communication session has been established. 
     
     
         14 . A method for providing service continuity with respect to a registration of a mobile terminal (UE), at a control server of an IP Multimedia Subsystem (IMS) network, while a CS-communication session between the UE and a switching server (MSC), of a circuit-switched (CS) network is established, the method comprising:
 the MSC sending for the duration of the established CS-communication session, a control information to the control server to update a registration timer in the control server; and   the control information initiating a termination of the registration of the UE at the IMS network, when the registration timer expires.   
     
     
         15 . The method according to  claim 14 , wherein the control server, after receiving the control information from the MSC, updates the registration timer when the registration timer approaches expiration. 
     
     
         16 . The method according to  claim 14 , wherein the MSC initiates the update of the registration timer in the control server by
 requesting the registration timer value from the control server of the IMS network and,   after receiving the registration timer value and detecting that the registration timer is near expiration, triggering the control server of the IMS network to update the registration timer.   
     
     
         17 . A switching server (MSC), of a circuit-switched network (CS) for providing service continuity with respect to a registration of a mobile terminal (UE), at a control server of an IP Multimedia Subsystem (IMS) network, while a communication session between the UE and the MSC is established, wherein the control server comprises a registration timer which is used for initiating a termination of the registration of the UE at the IMS network, when the registration timer expires, the MSC comprising:
 a transmitting unit for sending a control information to the control server, the control information including information that the UE to update the registration timer.   
     
     
         18 . The switching server, MSC, according to  claim 17 , wherein the transmitting unit of the MSC is adapted to trigger the control server to terminate an updating of the registration timer in the control server after the communication session between the UE and the MSC is released. 
     
     
         19 . A switching server (MSC), of a circuit-switched (CS) network for providing service continuity with respect to a registration of a mobile terminal (UE), at a control server of an IP Multimedia Subsystem (IMS) network, for the duration of a CS-communication session between the UE and the MSC, wherein the control server comprises a registration timer which is used for initiating a termination of the registration of the UE at the IMS network, when the registration timer expires, the MSC comprising:
 a transmitting unit for sending to the control server a request for the registration timer value from of the IMS network and a trigger to update the registration timer when the registration timer is near expiration   a receiving unit for receiving the registration timer value from the control server of the IMS network,   a decision unit for making a decision to trigger an update of the registration timer, when the registration timer is near expiration.