Communication device and communication method with improved handover

1. A communication device comprising: a memory; and

a control circuit coupled to the memory and configured to

perform a communication with a first base station based on a first communication protocol for a call,

when the call is disconnected, store, in the memory, state information indicating a state of the call before the disconnection and destination information indicating a destination of the call in association with the state information for the call,

after the disconnection, perform a first search for a second base station which is configured to communicate based on the first communication protocol,

when the first search failed, perform a second search for and identify a third base station which is configured to communicate based on a second communication protocol different from the first communication protocol,

perform waiting at the third base station and restore the state of the call before the disconnection based on the state information stored in the memory, and

when the waiting is started and the state information in the memory indicates that the state of the call is an on-hold state, execute a connection process to the destination identified by the destination information, and set the call in the on-hold state after restoring the call based on the state information stored in the memory.

2. The communication device according to claim 1 , wherein

the communication is a speech communication, and

the state information includes at least one of first information which indicates the speech communication is in a first period from an establishment of the speech communication to an end of the speech communication, second information which indicates the speech communication is in a second period from the transmission of the call to the establishment of the speech communication, and third information which indicates the speech communication is in a third period other than the first period and the second period.

3. The communication device according to claim 2 , wherein the state information includes fourth information which indicates whether the call is a voice call or a video call in which an image and sound are communicated.

4. The communication device according to claim 3 , wherein the state information includes fifth information which indicates whether the call is transmitted from the communication device or the call is received from the communication device.

5. The communication device according to claim 4 , wherein the control circuit is further configured to store destination information indicating a destination of the call in association with the state information for the call.

6. The communication device according to claim 1 , wherein the second base station is different from the first base station.

7. The communication device according to claim 1 , wherein the first communication protocol is LTE and the second communication protocol is 3G.

8. The communication device according to claim 1 , wherein the control circuit is further configured to

store in the memory destination information indicating a destination of the call in association with the state information,

when the state information indicates that the call is in a process of speech communication or the state information indicates that the call is in a process of being established is stored in the memory, put the call in the on-hold state after restoring the call, and transmit the call to the destination when the waiting is started, and

when the state information indicates that the call is in the on-hold state is stored in the memory, and when the waiting is started, transmit the call to the destination.

9. The communication device according to claim 1 , wherein the control circuit is further configured to, after restoring the call, put the call in the on-hold state after notifying a user that the call is to be put on hold.

10. The communication device according to claim 1 , wherein the control circuit is further configured to

receive an instruction as to whether to put the call in the on-hold state or put the call into speech communication after restoring of the call, and

after restoring the call, put the call in the on-hold state or put the call into speech communication based on the instruction.

11. The communication device according to claim 1 , wherein the memory is further configured to store setting information specifying whether to put the call in the on-hold state or to put the call into speech communication after restoring of the call, and

wherein the control circuit is further configured to, after restoring of the call, put the call on-hold or put the call into speech communication based on the setting information held in the memory.

12. The communication device according to claim 1 , wherein the control circuit is further configured to

receive an instruction as to whether to restore the state of the call when the disconnection of the call occurs, and

where the instruction to restore the state of the call is received, restore the state of the call after the disconnection.

13. The communication device according to claim 1 , wherein the memory is further configured to store setting information specifying whether to restore the state of the call, and

wherein the control circuit is further configured to, when the setting information held in the memory specifies restoration of the state of the call, restore the state of the call after the disconnection.

14. The communication device according to claim 1 , wherein the memory is further configured to store the destination information identifying another communication device as a communication partner of the communication device, and

wherein the control circuit is further configured to restore the state of the call where a caller device of the call coincides with the another communication device identified by the destination information after the disconnection.

15. The communication device according to claim 1 , wherein the second base station is identical to the first base station.

16. A communication method using a communication device including a memory, the method comprising:

performing a communication with a first base station based on a first communication protocol for a call;

when the call is disconnected, storing, in the memory, state information indicating a state of the call before the disconnection and destination information indicating a destination of the call in association with the state information for the call;

after the disconnection, performing a first search for a second base station which is configured to communicate based on the first communication protocol;

when the first search failed, performing a second search for and identifying a third base station which is configured to communicate based on a second communication protocol different from the first communication protocol,

performing waiting at the third base station and restore the state of the call before the disconnection based on the state information stored in the memory; and

when the waiting is started and the state information stored in the memory indicates that the state of the call is an on-hold state, execute a connection process to the destination identified by the destination information, and set the call in the on-hold state after restoring the call based on the state information stored in the memory.