In a simple conventional system, everything is dictated by the frequency being used, and every site with that frequency transmits the call whether there is someone there to listen to it or not.

On a trunked system, only radios that are allowed to hear the conversation are allocated a frequency.  Sites with no radios in the call are not included, adding to the network's efficiency.

However, in order to achieve this level of efficiency, a different method for identification is required, and the GRN uses two main forms of identification.

Firstly, there is the radio ID.  This allows the system to determine if the radio is a valid user or not, as well as system information about the user’s profile (such as whether the radio can make telephone interconnect calls).

Secondly, there is a talkgroup ID.  Each time a user changes their talkgroup, the new talkgroup ID is transmitted to the network.  The talkgroup ID is stored with the radio ID, so that the system knows who to connect together when a call request is received for that particular talkgroup.