Circuit-switched and multimedia subsystem voice continuity with bearer path interruption

Abstract

The present invention maintains calls during transfers between different types of subsystems, even when there is a bearer path interruption at the user element due to the original connection from the transferring-out subsystem being dropped before the new connection in the transferring-in subsystem is established. The call signaling leg toward the remote endpoint of the remote party is held, while the call signaling leg toward the user element is moved from the transferring-out subsystem to the transferring-in subsystem and a new bearer path is established via the transferring-in subsystem. During transfers with a bearer path interruption, a portion of the bearer path leading to the remote endpoint may be connected to a media resource function, which will provide an announcement to the remote party. Once the user element is accessible in the transferring-in subsystem, the bearer path is further transferred to the user element via the transferring-in subsystem.

1 . A method comprising: 
 providing a signaling anchor point in a multimedia subsystem for a first access signaling leg and a remote access signaling leg for a voice call between a user element and a remote endpoint over a bearer path, the first access signaling leg provided for the user element via a transferring-out subsystem;    establishing a second access signaling leg toward a user element via a transferring-in subsystem;    replacing the first access signaling leg with the second access signaling leg, such that the second access signaling leg is anchored at the signaling anchor point; and    providing call signaling via the second access signaling leg and the remote signaling leg to transfer at least a portion of the bearer path connected to the user element from the transferring-out subsystem to the transferring-in subsystem, wherein one of the transferring-in subsystem and the transferring-out subsystem is the multimedia subsystem that supports the voice call over a packet session, and another of the transferring-in subsystem and the transferring out subsystem is a circuit-switched subsystem that supports the voice call over a circuit-switched connection.    
   
   
       2 . The method of  claim 1  wherein the multimedia subsystem is a third generation wireless packet network and the circuit-switched subsystem is a second generation wireless circuit-switched network.  
   
   
       3 . The method of  claim 1  wherein there is a perceptible delay between releasing the portion of the bearer path connected to the user element via the transferring-out subsystem and establishing the portion of the bearer path connected to the user element via the transferring-in subsystem.  
   
   
       4 . The method of  claim 3  further comprising effecting delivery of an audible announcement over a portion of the bearer path connected to the remote endpoint during the perceptible delay.  
   
   
       5 . The method of  claim 4  wherein effecting delivery of the audible announcement comprises providing call signaling via an intermediate access signaling leg and the remote signaling leg to transfer at least a portion of the bearer path connected to the user element from the transferring-out subsystem to a media resource function, which delivers the audible announcement to the remote endpoint via the bearer path.  
   
   
       6 . The method of  claim 5  wherein the portion of the bearer path connected to the user element in the transferring-out subsystem is initially transferred to the media resource function for delivery of the audible announcement during the perceptible delay, and is subsequently transferred to the user element via the transferring-in subsystem to reestablish the voice call.  
   
   
       7 . The method of  claim 1  further comprising receiving a request of the user element to transfer the voice call to the transferring-in subsystem.  
   
   
       8 . The method of  claim 7  further comprising sending to the user element a message indicating the transfer is being effected via the transferring-out subsystem.  
   
   
       9 . The method of  claim 8  wherein the user element will release access to the transferring-out subsystem and gain access to the transferring-in subsystem upon receiving the message.  
   
   
       10 . The method of  claim 7  wherein the user element will automatically release access to the transferring-out subsystem and gain access to the transferring-in subsystem upon sending the request.  
   
   
       11 . The method of  claim 7  wherein the request is generated from the user element when the user element determines a need to transfer the voice call.  
   
   
       12 . The method of  claim 7  wherein the request is originated from the user element using at least one of a multimedia subsystem address for a continuity control function, which provides the signaling anchor point, and a directory number within a circuit-switched subsystem, which is associated with the multimedia subsystem address.  
   
   
       13 . The method of  claim 7  wherein the request is sent via an Unstructured Supplementary Service Data (USSD) channel.  
   
   
       14 . The method of  claim 1  further comprising effecting subsequent transfers between the transferring-in and transferring-out subsystems.  
   
   
       15 . A service node comprising: 
 a communication interface; and    a control system associated with the communication interface and adapted to: 
 provide a signaling anchor point in a multimedia subsystem for a first access signaling leg and a remote access signaling leg for a voice call between a user element and a remote endpoint over a bearer path, the first access signaling leg provided for the user element via a transferring-out subsystem;  
 establish a second access signaling leg toward a user element via a transferring-in subsystem;  
 replace the first access signaling leg with the second access signaling leg, such that the second access signaling leg is anchored at the signaling anchor point; and  
 provide call signaling via the second access signaling leg and the remote signaling leg to transfer at least a portion of the bearer path connected to the user element from the transferring-out subsystem to the transferring-in subsystem, wherein one of the transferring-in subsystem and the transferring-out subsystem is the multimedia subsystem that supports the voice call over a packet session, and another of the transferring-in subsystem and the transferring out subsystem is a circuit-switched subsystem that supports the voice call over a circuit-switched connection.  
   
   
   
       16 . The service node of  claim 15  wherein the multimedia subsystem is a third generation wireless packet network and the circuit-switched subsystem is a second generation wireless circuit-switched network.  
   
   
       17 . The service node of  claim 15  wherein there is a perceptible delay between releasing the portion of the bearer path connected to the user element via the transferring-out subsystem and establishing the portion of the bearer path connected to the user element via the transferring-in subsystem.  
   
   
       18 . The service node of  claim 17  wherein the control system is further adapted to effect delivery of an audible announcement over a portion of the bearer path connected to the remote endpoint during the perceptible delay.  
   
   
       19 . The service node of  claim 18  wherein to effect delivery of the audible announcement, the control system is further adapted to provide call signaling via an intermediate access signaling leg and the remote signaling leg to transfer at least a portion of the bearer path connected to the user element from the transferring-out subsystem to a media resource function, which delivers the audible announcement to the remote endpoint via the bearer path.  
   
   
       20 . The service node of  claim 19  wherein the portion of the bearer path connected to the user element in the transferring-out subsystem is initially transferred to the media resource function for delivery of the audible announcement during the perceptible delay, and is subsequently transferred to the user element via the transferring-in subsystem to reestablish the voice call.  
   
   
       21 . The service node of  claim 15  wherein the control system is further adapted to receive a request of the user element to transfer the voice call to the transferring-in subsystem.  
   
   
       22 . The service node of  claim 21  wherein the control system is further adapted to send to the user element a message indicating the transfer is being effected via the transferring-out subsystem.  
   
   
       23 . The service node of  claim 22  wherein the user element will release access to the transferring-out subsystem and gain access to the transferring-in subsystem upon receiving the message.  
   
   
       24 . The service node of  claim 21  wherein the user element will automatically release access to the transferring-out subsystem and gain access to the transferring-in subsystem upon sending the request.  
   
   
       25 . The service node of  claim 21  wherein the request is generated from the user element when the user element determines a need to transfer the voice call.  
   
   
       26 . The service node of  claim 21  wherein the request is originated from the user element using at least one of a multimedia subsystem address for a continuity control function, which provides the signaling anchor point, and a directory number within a circuit-switched subsystem, which is associated with the multimedia subsystem address.  
   
   
       27 . The service node of  claim 21  wherein the request is sent via an Unstructured Supplementary Service Data (USSD) channel.  
   
   
       28 . The service node of  claim 15  wherein the control system is further adapted to effect subsequent transfers between the transferring-in and transferring-out subsystems.