Patent ID: 7792540

Claim:
A mobile terminal for synchronizing with a server in a shadow area of service in a push-to-talk (PTT) service system, the mobile terminal comprising: means for establishing a session with the server; means for transmitting to and receiving from the server a real time transport control protocol (RTCP) packet or a real time transport protocol (RTP) packet; and means for ending the session established with the server if the RTCP packet is not received by the server for a specific time period, the RTCP packet being an alive report packet transmitted from a different mobile terminal that does not have permission to transmit a talk burst, wherein the mobile terminal is synchronized with the server when in an area having no radio coverage, wherein the synchronization between the server and the mobile terminal in the area having no radio coverage is maintained by periodic verification using the alive report packet, wherein a period of the alive report packet is flexibly set according to a communication network to have no influence on the quality of the RTP packet, and wherein the mobile terminal has permission to transmit the talk burst and transmits only the RTP packet to the server to maintain the quality of the RTP packet.