Method and terminal and system for a poc group session setup in poc system

A method, a terminal and a system for establishing a PoC(Push-to-talk over Cellular) group session in a PoC system are provided to dynamically manage related XML(eXtensible Markup Language) data by generating, correcting and deleting IRS(Invitation Reservation Service) parameters in the same manner as target URI(Uniform Resource Identifier) list information. A PoC terminal(400) sets an IRS-related information defining session initiation conditions in a PoC XDMS(XML Document Management Server)(420) and requests an IRS for initiating a session from a PoC server(430) by using an IRS ID. The PoC XDMS(420) transmits IRS ID for identifying the IRS-related information to the PoC terminal(400). When the IRS request message is received, the PoC server(430) performs session initiation by using the IRS ID.