Handoff for Cellular and Internet Protocol Telephony

Abstract

A telephone system supports communication with user devices over both a cellular radio network as well as over an Internet Protocol (IP) network, and enables roaming and active call handoff between cellular and IP domains. Components of the system interact with conventional cellular telephone systems, for example, by emulating behavior of control components, providing proxy services for conventional components, transporting cellular telephone control communications over IP connections, or by simulating cellular operating characteristics of user devices operating in an IP domain.

1 . A method for handoff of telephone sessions comprising:
 maintaining an active telephone session between a mobile unit and a telephone system over the data communication system;   while maintaining the session over the data communication system, determining information associated with a radio system associated with the telephone system; and   handing off the active telephone session from the data communication system to the radio system according to the determined information.   
   
   
       2 . The method of  claim 1  wherein the information associated with the radio system includes signal characteristics on the radio system. 
   
   
       3 . The method of  claim 1  wherein the information associated with the radio system includes radio channel information for the radio system. 
   
   
       4 . The method of  claim 1  wherein the telephone system comprises a cellular telephone system. 
   
   
       5 . The method of  claim 1  wherein the data communication system comprises a data network. 
   
   
       6 . The method of  claim 5  wherein the data network comprises an Internet Protocol (IP) network. 
   
   
       7 . The method of  claim 5  wherein the data network comprises a wireless local area network. 
   
   
       8 . The method of  claim 1  further comprising, prior to maintaining the session over the data communication network:
 maintaining the active telephone session between the mobile unit over a radio system of the telephone system, including receiving radio channel information at the mobile unit over the radio system;   establishing communication between the mobile unit and the telephone system over a data communication system; and   handing off the active telephone session from the radio system of the telephone system to the data communication system.   
   
   
       9 . The method of  claim 8  wherein receiving radio channel information at the mobile unit includes receiving a candidate channel list for a cellular telephone system. 
   
   
       10 . The method of  claim 9  wherein measuring the signal characteristics includes measuring signal strength characteristics for each of the channels of the candidate channel list. 
   
   
       11 . The method of  claim 10  further comprising providing the candidate channel list to the telephone system after establishing communication between the mobile unit and the telephone system, and receiving the candidate list from the telephone system prior to handing off the session from the data network to the radio system. 
   
   
       12 . A method comprising:
 communicating telephone system control information between a dual-mode device and the telephone system, including passing the telephone control information over a data network encapsulated in a data network communication protocol; and   performing a handoff of the dual mode device between the telephone system and the data network using the encapsulated telephone control information.   
   
   
       13 . The method of  claim 12  wherein the data network communication protocol includes a session control protocol. 
   
   
       14 . The method of  claim 13  wherein the session control protocol includes Session Initiation Protocol (SIP). 
   
   
       15 . The method of  claim 12  wherein the telephone system control information includes telephone system signal characteristic information. 
   
   
       16 . The method of  claim 12  wherein the telephone system control information includes telephone system radio channel information. 
   
   
       17 . A dual mode device for communicating over a telephone system and a data network comprising:
 a data network client, including components for establishing communication sessions over the data network;   a telephone system client, including components for establishing communication sessions over the telephone system; and   a service controller coupled to the data network client and to the telephone system client that enables a handoff of an active communication session between the data network client and the telephone system client.   
   
   
       18 . The device of  claim 17  wherein the data network client is configured to send and/or receive encapsulated telephone system control information, and pass the telephone control information to the service controller. 
   
   
       19 . The device of  claim 18  wherein the network client is configured to send and/or receive the telephone system control information in session control protocol messages.