Priority Levels for the Busy Queue

Radio traffic on the BRICS/MARCS-IP trunked radio system, in the busy queue, is prioritized in two ways:

  • by the type of talkgroup, when all frequencies are in use
  • by the type of call on the same talkgroup, when users try to talk at the same time

This priority system only applies when the system is so congested that there are more requests to transmit on talkgroups at a particular tower site than there are channels available, at that site, at the time. The priority levels sort the queue of people waiting to talk, allowing higher priority users on higher priority talkgroups to be first in line. This busy period is often as short as a few seconds, or even less than a second.

There are ten priority levels available. Level 1 is reserved for emergency alarms and calls. The same ten-level priority system applies to both talkgroups and radios. When a radio enters the busy queue and is waiting for a channel to be granted, the system evaluates the priority of both the talkgroup and the radio user. For the purpose of sorting by talkgroup first, priority levels 2 through 6 are assigned to talkgroups. Radios are assigned to priority levels 8 through 10.

Priority Type Description Butler County Examples
1 Emergency Emergency alarms and calls
2 Talkgroups Primary Dispatch Talkgroups L MAIN; F MAIN
3 Talkgroups Incident / Interoperability Talkgroups LAW; FIRE; TAC; EVNT; MA
4 Talkgroups Hailing / Coordination 09 CALL; 09 HELP; IPSAP; HOSP
5 Talkgroups Public Safety Secondary Talkgroups L OPS; F OPS; P OPS
6 Talkgroups Low Priority Talkgroups
7 Open
8 Radio Users Dispatch Centers / System
9 Radio Users Public Safety Users
10 Radio Users Non-Public Safety Users

Emergency and Dispatcher Priority

Within the same talkgroup, different types of calls have different priorities.  In general, they are:

  1. Emergency calls
  2. Dispatcher consoles
  3. All other voice traffic (field users)

Normally, a dispatch console has priority on a talkgroup.  Field users (portables and mobiles) can not “talk over” a dispatcher, meaning that while a dispatcher is speaking to all the users on the talkgroup, field users can’t interrupt and take over the talkgroup to speak to all users.

Field users can not talk over each other. If one field user is transmitting, and another user attempts to transmit on the same talkgroup, that attempt will be rejected. The system refers to this as a can’t interrupt reject – and the user attempting to interrupt will be rejected with a prohibit tone.

If you key up, and the system grants you access to the channel, you’ll hear (on most Motorola radios):

Click to hear the ‘Talk Permit’ tone

If you key up while another field user is talking, you’ll hear (on most Motorola radios):

Click to hear the ‘Prohibit’ tone

The “can’t interrupt” reject does not apply to dispatchers. The dispatcher has the ability to interrupt a field user’s call to address all other users on the same talkgroup. While a field user is transmitting, the dispatcher may transmit “over” that user and reach everyone (except the originally transmitting field user, because the radio cannot transmit and receive simultaneously).


  • Radio 1 is transmitting. Radio 2, Radio 3, and the dispatcher are receiving Radio 1.
  • Dispatcher keys on the same talkgroup, overriding Radio 1.
  • Radio 2 and Radio 3 receive the dispatcher even though Radio 1 is transmitting.

Dispatch consoles have the capability of full duplex. This is why a field user can transmit during a dispatcher’s transmission, without being rejected.

From: Wikipedia

A half-duplex system provides for communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.

A full-duplex, or sometimes double-duplex system, allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex, since they allow both callers to speak and be heard at the same time.

If a field user calls while the dispatcher is transmitting, the dispatch center will receive it. Everyone else in the field will still hear the dispatcher, because the dispatcher has priority. If your dispatch center receives radio audio through the headset, the transmitting dispatcher will hear the calling person at their console. At centers with radio audio from desktop speakers only, the calling person will be heard at all other console positions.


  • A dispatcher is making a lengthy BOLO (be on the lookout) announcement.
  • Radio 1, Radio 2, and Radio 3 are listening to the BOLO.
  • Radio 1 has important traffic and keys the mic during the dispatcher’s BOLO.
  • The dispatch center receives traffic from Radio 1 during the BOLO
  • All other users (Radio 2 and Radio 3) continue to hear the BOLO.
  • The dispatcher can choose to stop broadcasting the BOLO to address Radio 1 if needed.

The dispatch console is only overridden by a field user when they are making an emergency call.  After pressing an emergency alarm, subsequent voice traffic from the radio is sent as an emergency call and has the highest priority on the radio system. A user making an emergency call can “talk over top of” a dispatcher and all units on the same talkgroup will hear the emergency call.