Abstract: A push-to-talk data transmission device that creates and manages groups of participating terminals dynamically. A PoC data transmission device is deployed to support push-to-talk sessions in a prescribed area. This device has a data transmitter that broadcasts a group profile repetitively in the prescribed area. The group profile is a set of parameters that prompt terminals in the prescribed area to send back their respective unique identifiers to join a push-to-talk session. A counter in the PoC data transmission device counts the number of responses returned from the terminals, and the data transmitter broadcasts a new group profile if the number of responses has reached a predetermined threshold.

Abstract: A method for duplicating a home agent including an address correspondence maintaining unit for maintaining a destination address of a mobile terminal in correspondence with a home address of the mobile terminal, and a transferring unit for encapsulating an IP packet addressed to the home address of the mobile terminal and transferring the encapsulated IP packet to the destination address of the mobile terminal is disclosed. The method includes the steps of setting a home agent address, which is the same as a home agent address of an operation system home agent, to a standby system home agent, and receiving a location registration request, which is sent from the mobile terminal and addressed to the operation system home agent, with the standby system home agent.