A talkgroup is a predefined label, or form of identification (ID) used by the network to group users together.  When a user selects a talkgroup in their radio, the talkgroup ID (as well as the radio ID) is transmitted to the central site.

When a call is made via that talkgroup, the central site knows which radios are using that talkgroup and needs to be included in the call.

For example, there may be 10 people that have the same talkgroup selected on their radio, and they may be spread across 4 different remote sites.

When one of the users initiates a call, the central site (in coordination with the remote sites) will allocate a channel at each of the four remote sites, and connect them together.  Each remote site will tell the users within its coverage to move to the allocated channel.  This setup process generally takes less than half a second.

The channel is allocated by the network, not selected by the user.  Therefore, the word 'talkgroup' is used instead rather than 'channel' when determining if you are able to talk to another person.

By simply changing the talkgroup within the radio, the user moves from one group of people to a different group.

Generally, each agency has their own talkgroups.  Other agencies can not access these talkgroups.  The exception are the 'ESO' common channels, which are for use during joint agency exercises, enabling users from different agencies to talk to each other.  The use of ESO channels should be requested from the NOCC before use.  The NOCC will allocate a specific ESO channel for the period of the exercise, thus ensuring orderly and exclusive use of these channels.