When a radio user wishes to make a Talkgroup call on the GRN, they simply select the required talkgroup on their radio and then press the "Press To Talk" (PTT) button.

As soon as this happens, the radio automatically communicates through the nearest GRN site via data links to the Zone Controller at the GRN NOCC. The Zone Controller assesses which radio users are members of that particular talkgroup and transmits the message to all the relevant sites to be broadcast to the necessary users. At each of the relevant sites, a voice channel is dynamically allocated for the call to be established, and individual radios on that talkgroup move to that channel.

When the talkgroup call is finished, radios move back to the control channel, and the voice channel is released ready to be allocated to the next user.

Only the sites with users of that particular talkgroup call are connected (i.e. if no one in that talkgroup is affiliated to a site, then that site would not transmit that call).  This adds to the efficiency of the network.

It typically takes less than half a second for this process to be completed.