Communication terminal apparatus, communication system and seamless handover method

A communication terminal apparatus comprising a first radio interface and a second radio interface for carrying out communication using different call control protocol stacks between the first and second radio interfaces, wherein:

• while call control using the first radio interface is in progress, even if the conditions to perform handover from the first radio interface to the second radio interface are met, handover is not performed;
• and
• handover is performed from the first radio interface to the second radio interface after the call control using the first interface is finished.

A communication system comprising a plurality of different networks and a communication terminal apparatus comprising radio interfaces for carrying out communication with the plurality of networks, the communication terminal apparatus starting the radio interfaces to perform call control, the communication system comprising:

• a call state mapping table that performs mapping by associating a message in a call state protocol stack of the communication terminal apparatus with a message in a call state protocol stack used in a certain network among the plurality of networks;
• and
• a call control section that looks up the call state mapping table, finds another predetermined message mapped by the predetermined message, changes the state to the another predetermined message and executes subsequent processing.

A method of seamless handover from a first radio interface and a second radio interface for a communication terminal apparatus comprising the first radio interface and the second radio interface for carrying out communication using different call control protocol stacks between the first and second radio interfaces,

• wherein, when handover is performed from the first radio interface to the second radio interface while call control using the first radio interface is in progress, a call state in a call control protocol stack being executed using the first radio interface is maintained by a call control protocol stack to be executed using the second radio interface.

A method of seamless handover from a first radio interface and a second radio interface for a communication terminal apparatus comprising the first radio interface and the second radio interface for carrying out communication using different call control protocol stacks between the first and second radio interfaces,

• wherein, while call control using the first radio interface is in progress, even if the conditions to perform handover from the first radio interface to the second radio interface are met, handover is not performed, and handover is performed from the first radio interface to the second radio interface after the call control using the first interface is finished.