Normally, the lowest numbered channel at a site on a DMR network is the control channel. See in the diagram below, the channel number indicates the position of the physical channel at the site. For example, here we have Site 1. Site 1 consists of a cabinet with physical channels located inside the cabinet.

Channel 1 will be the first designated channel, consisting of a transmitter and a receiver. Channel 2 will duplicate this hardware. Channel 3, the same, up to potentially 20 channels at the site. These are physical channels. Each of the channels can operate in TDMA mode, which means two logical channels for each of the physical channels indicated. The control channel will be the first logical channel on physical channel number one. If Channel 1 fails, the next channel, Channel 2, will take over as the control channel.

It is the first time slot that will be the control channel. This will continue if we have successive failures. When the channel is brought back into service, it reverts to being the control channel once more.

The major functions of a control channel include:

• The management and control of registration requests from mobiles, portables and allow access to channels.
• Processing of call requests to and from subscriber units in the field and to any line connected dispatcher or other devices.
• Allocation of a logical channel for each call.
• Broadcasting system information to the subscriber units, such as call time length.
• Provides location management information by registration.
• And lastly, it provides short data messaging services.