Providing improved post-dial delay at an originating terminal

Abstract

To provide expedited ringback at an originating terminal, a call request is sent from the originating terminal to a destination device over an Internet Protocol (IP) network. Local resource reservation is performed by the originating terminal after sending the call request. A first message is received by the originating terminal prior to the originating terminal sending a second message indicating that local resource reservation has been performed, the first message for indicating that alerting is being performed at the destination device. In response to receiving the first message and determining that the local resource reservation has been performed, a ringback indicator is generated by the originating terminal.

1 . A method of operating an Internet Protocol network to establish a call between an originating terminal and a destination terminal, the method comprising, at a call control function of the Internet Protocol network:
 receiving a call request from the originating terminal the call request requesting establishment of a packet-switched call session with the destination terminal over the Internet Protocol network;   performing local resource reservation for the destination terminal;   performing local resource reservation for the originating terminal; and   before completing local resource reservation for the originating terminal, sending a ring message to the originating terminal to enable expedited ringback at the originating terminal.   
     
     
         2 . The method of  claim 1 , wherein the call control function of the Internet Protocol network comprises a first call control element which serves the originating terminal and a second call control element which serves the destination terminal:
 the first call control element:
 receiving the call request from the originating terminal; 
 sending the call request from the first call control element to the second call control element; 
 performing the local resource reservation for the originating terminal; and 
 sending the ring message to the originating terminal before completing the local resource reservation for the originating terminal to enable expedited ringback at the originating terminal; and 
   the second call control element:
 receiving the call request from the first call control element; 
 sending the call request to the destination terminal; and 
 performing the local resource reservation for the destination terminal. 
   
     
     
         3 . The method of  claim 2 , wherein:
 the second call control element sends a ring message to the first call control element when local resource reservation for the destination terminal is complete; and   the first call control element sends the ring message to the originating terminal responsive to receiving the ring message from the second call control element.   
     
     
         4 . The method of  claim 2 , comprising:
 sending an alert message from the first call control element to the second call control element when resource reservation for the originating terminal is complete;   receiving the alert message at the second call control element; and   sending an alert message from the second call control element to the destination terminal responsive to receiving the alert message at the second call control element.   
     
     
         5 . The method of  claim 4 , wherein the first call control element sends the alert message to the second call control element responsive to an indication that local resource reservation for the originating terminal has been completed. 
     
     
         6 . The method of  claim 5 , wherein the second call control element sends an alert message to the destination terminal responsive to receipt of the alert message from the first call control element. 
     
     
         7 . The method of  claim 4 , wherein the alert message is a session initiation protocol (SIP) PRACK message. 
     
     
         8 . The method of  claim 4 , wherein the alert message is a SIP Update message. 
     
     
         9 . The method of  claim 8 , wherein the first call control element sends a SIP PRACK message to the second call control element before local resource reservation for the originating terminal has been completed. 
     
     
         10 . The method of  claim 9 , wherein the first call control element sends a SIP PRACK message to the second call control element responsive to receiving the SIP PRACK message from the originating terminal. 
     
     
         11 . The method of  claim 10 , wherein the second call control element sends a SIP PRACK message to the destination terminal responsive to receiving the SIP PRACK message from the first call control element. 
     
     
         12 . The method of  claim 7 , wherein:
 the second call control element sends a SIP OK message to the first call control element responsive to receiving a SIP OK message from the destination terminal after sending the SIP PRACK message to the destination terminal; and   the first call control element sends a SIP OK message to the originating terminal responsive to receiving the SIP OK message from the second call control element.   
     
     
         13 . The method of  claim 12 , wherein the SIP OK message is a SIP Invite message. 
     
     
         14 . The method of  claim 12 , wherein:
 the first call control element sends a SIP ACK message to the second call control element responsive to receiving a SIP ACK message from the originating terminal after sending the SIP OK message to the originating terminal; and   the second control element sends a SIP ACK message to the destination terminal responsive to receiving the SIP OK message from the first call control element.   
     
     
         15 . The method of  claim 14 , comprising establishing a bearer path between the originating terminal and the destination terminal after exchange of he SIP OK and SIP ACK messages. 
     
     
         16 . The method of  claim 8 , wherein:
 the second call control element sends a SIP OK message to the first call control element responsive to receiving a SIP OK message from the destination terminal after sending the SIP Update message to the destination terminal; and   the first call control element sends a SIP OK message to the originating terminal responsive to receiving the SIP OK message from the second call control element.   
     
     
         17 . The method of  claim 16 , wherein the SIP OK message is a SIP Invite message. 
     
     
         18 . The method of  claim 16 , wherein:
 the first call control element sends a SIP ACK message to the second call control element responsive to receiving a SIP ACK message from the originating terminal after sending the SIP OK message to the originating terminal; and   the second control element sends a SIP ACK message to the destination terminal responsive to receiving the SIP OK message from the first call control element.   
     
     
         19 . The method of  claim 18 , comprising establishing a bearer path between the originating terminal and the destination terminal after exchange of he SIP OK and SIP ACK messages. 
     
     
         20 . The method of  claim 1 , wherein the call request is a SIP Invite message. 
     
     
         21 . The method of  claim 1 , comprising sending an alert message from the call control function to the destination terminal when resource reservation for the originating terminal is complete. 
     
     
         22 . The method of  claim 21 , wherein the call control function sends the alert message to the destination terminal responsive to receiving an indication from the originating terminal that local resource reservation for the originating terminal has been completed. 
     
     
         23 . The method of  claim 21 , wherein the alert message is a session initiation protocol (SIP) PRACK message. 
     
     
         24 . The method of  claim 21 , wherein the alert message is a SIP Update message. 
     
     
         25 . The method of  claim 23 , wherein the call control function sends a SIP OK message to the originating terminal responsive to receiving a SIP OK message from the destination terminal after sending the alert message to the destination terminal. 
     
     
         26 . The method of  claim 25 , wherein the SIP OK message is a SIP Invite message. 
     
     
         27 . The method of  claim 25 , wherein the call control function sends a SIP ACK message to the destination terminal responsive to receiving a SIP ACK message from the originating terminal after sending the SIP OK message to the originating terminal. 
     
     
         28 . The method of  claim 27 , comprising establishing a bearer path between the originating terminal and the destination terminal after exchange of he SIP OK and SIP ACK messages. 
     
     
         29 . The method of  claim 24 , wherein the call control function sends a SIP OK message to the originating terminal responsive to receiving a SIP OK message from the destination terminal after sending the SIP Update message to the destination terminal. 
     
     
         30 . The method of  claim 29 , wherein the SIP OK message is a SIP Invite message. 
     
     
         31 . The method of  claim 30 , comprising establishing a bearer path between the originating terminal and the destination terminal after exchange of he SIP OK and SIP ACK messages.