Apparatus and method for controlling PTT service by multiplexing call originator and floor arbitrator

1. A method of Mission Critical Push to Talk (MCPTT) service performed by a mobile terminal, the method comprising:

generating, at the mobile terminal, a group call announcement for off-network Mission Critical Push to Talk (MCPTT) service, the group call announcement for off-network MCPTT service comprising a field indicating a period of the group call announcement for off-network MCPTT service;

controlling a transceiver to periodically transmit, to one or more mobile terminals and based on the period, the group call announcement for off-network MCPTT service comprising the field indicating the period;

in response to the transmitted group call announcement for off-network MCPTT service, receiving a response from the one or more mobile terminals; and

establishing, based on the response from the one or more mobile terminals, a group call with the one or more mobile terminals by setting a direct wireless communication with the one or more mobile terminals.

2. The method of claim 1 , further comprising controlling the transceiver to continue the periodic transmission of the group call announcement for off-network MCPTT service after establishing the group call with the one or more mobile terminals.

3. The method of claim 1 , further comprising determining the period of the group call announcement for off-network MCPTT service,

wherein the period of the group call announcement for off-network MCPTT service is determined per group.

4. The method of claim 1 , further comprising:

determining that the mobile terminal is off-network; and

determining the periodic transmission of the group call announcement for off-network MCPTT service without using a radio access network.

5. The method of claim 1 , further comprising:

while the mobile terminal is on-network, establishing a connection with a floor control server and performing a group call of on-network MCPTT service through a mobile communication with a radio access network.

6. The method of claim 1 , further comprising:

receiving, by the mobile terminal and from a call originating mobile terminal, another group call announcement for off-network MCPTT service comprising a field indicating a different period of the another group call announcement for off-network MCPTT service; and

establishing, based on the received another group call announcement for off-network MCPTT service, another group call with the call originating mobile terminal.

7. A mobile terminal comprising:

a transceiver to transmit and receive a wireless signal; and

a processor operationally coupled to the transceiver and configured to:

generate a group call announcement for off-network Mission Critical Push to Talk (MCPTT) service, the group call announcement for off-network MCPTT service comprising a field indicating a period of the group call announcement for off-network MCPTT service;

control the transceiver to periodically transmit, to one or more mobile terminals and based on the period, the group call announcement for off-network MCPTT service comprising the field indicating the period; and

establish a group call with the one or more mobile terminals by setting a direct wireless communication with the one or more mobile terminals.

8. The mobile terminal of claim 7 , wherein the processor is further configured to control the transceiver to periodically transmit the group call announcement for off-network MCPTT service after establishing the group call with the one or more mobile terminals.

9. The mobile terminal of claim 7 , wherein the processor is further configured to determine the period of the group call announcement for off-network MCPTT service, and

wherein the period of the group call announcement for off-network MCPTT service is determined per group.

10. The mobile terminal of claim 7 , wherein the processor is further configured to determine that the mobile terminal is off-network and to determine the periodic transmission of the group call announcement for off-network MCPTT service without using a radio access network.

11. The mobile terminal of claim 7 , wherein, while the mobile terminal is on-network, the processor is further configured to establish a connection with a floor control server and to perform a group call of on-network MCPTT service through a mobile communication with a radio access network, and

wherein the processor is further configured to establish a media plane for controlling at least one of a media transmission path for the group call of on-network MCPTT service, a voice transmission right, and a codec conversion.

12. The mobile terminal of claim 7 , wherein the group call announcement for off-network MCPTT service comprises information about a group call.

13. The mobile terminal of claim 7 , wherein the transceiver receives, from a call originating mobile terminal, another group call announcement for off-network MCPTT service comprising a field indicating a different period of the another group call announcement for off-network MCPTT service, and

wherein the processor is configured to establish, based on the received another group call announcement for off-network MCPTT service, another group call with the call originating mobile terminal.

14. A mobile terminal comprising:

a transceiver to receive, from a call originating mobile terminal, a group call announcement for off-network Mission Critical Push to Talk (MCPTT) service, the group call announcement for off-network MCPTT service comprising a field indicating a period of the group call announcement for off-network MCPTT service; and

a processor operationally coupled to the transceiver and configured to:

identify the field indicating the period of the group call announcement for off-network MCPTT service from the received group call announcement; and

establish a group call with a group of mobile terminals including the call originating mobile terminal by setting a direct wireless communication with the group of mobile terminals,

wherein the processor is configured to generate another group call announcement for off-network MCPTT service comprising a field indicating a different period of the another group call announcement for off-network MCPTT service,

wherein the transceiver periodically sends, based on the different period, the another group call announcement for off-network MCPTT service comprising the field indicating the different period, and

wherein the mobile terminal is a call originating mobile device for the another group call announcement for off-network MCPTT service.

15. The mobile terminal of claim 14 , wherein the processor is further configured to continuously monitor, based on the period, a periodic reception of the group call announcement for off-network MCPTT service after establishing the group call with the group of mobile terminals.

16. The mobile terminal of claim 14 , wherein, while the mobile terminal is on-network, the processor is further configured to establish a connection with a floor control server and to perform a group call of on-network MCPTT service through a mobile communication with a radio access network.

17. The mobile terminal of claim 14 , wherein the processor is further configured to determine a change of the call originating mobile terminal when the mobile terminal fails to detect a periodic reception of the group call announcement for off-network MCPTT service.

18. The mobile terminal of claim 14 , wherein the processor is further configured to determine a change of the call originating mobile terminal based on a threshold associated with the period.

19. The mobile terminal of claim 14 , wherein the processor is further configured to determine a change of the call originating mobile terminal based on a reception state of media data.

20. The mobile terminal of claim 14 , wherein the processor is further configured to determine a change of the call originating mobile terminal based on ranking information of call originator candidates;

wherein the ranking information of call originator candidates is pre-configured based on a topology of mobile terminals; and

wherein the processor is further configured to reset a timer based on the period.