Terminal A terminal is any radio on the network. Some terminals are not shaped like your typical radios, however, such as Picorgros's Data Modem, which looks like a computer device. Terminals may be a hand-held radio, a radio mounted in a vehicle, or something like a barcode scanner. Terminals either communicate with other terminals in Direct Mode, or participated in a trunking infrastructure.
Infrastructure Infrastructure is the collection of components allowing terminals to talk to each other. An all-inclusive component list involving antennas, base stations, towers, and IP networking.
Base Station A base station is a radio on the infrastructure often located at a tower site for wide-area communications. Terminals connect to base stations, and if the talkgroup requires multi-site access, the base station will send the signals onto the IP network.Using US language, a base station would be called a trunking repeater.


Trunking is a process of allowing more than one user to operate on a frequency. TETRA base stations trunk all communications, as the 4 time-slots inside the carrier handle different kinds of traffic. With a networked infrastructure, this trunking may be multi-site.
Trunked Mode
TETRA supports two communications modes: TMO (Trunked Mode) and DMO (Direct Mode). Trunked mode requires a base station and infrastructure to manage the communications, and provides the complete featureset of TETRA operations.
Direct Mode
DMO (Direct Mode) is a TETRA mode where the radios are operating without a base station network, either by choice, or because no networks are in range. Most TETRA functions are available to users. DMO allows users to setup ad-hoc networks with repeaters, but trunked services are not available.
Time Slot
A TETRAtrunked carrier is 25 kHz wide, and it contains 4 slots, interchangably called a time slot, or a channel. One of those slots per site is the Master Control Channel (MCH) that handles the administration of the terminals, along with any SDS traffic. Other slots may be configured for data and vocal use. Direct Mode does not have an MCH or SCHs.
Master Control Channel A Master Control Channel (MCH) is a time slot that handles administrative traffic on a TMO network. The MCH registers terminals, roams them, manages any encryption, and regulates communication priorities. The MCH will also pass SDS data, such as short text messages, status messages, and GPS location information.
Secondary Control Channel An SCH may be configured if the MCH becomes overloaded. Some infrastructure vendors support more than one SCH, and some systems may dynamically allocate the SCH channel depending on system load.
Repeater A TETRA Repeater is a radio on a DMO network that repeats signals. A repeater is not a device at a tower location in the usual sense... those devices are called base stations.

A Gateway is a mobile TETRA terminal that bridges a TMO talkgroup with a DMO talkgroup. An example would be a firetruck that is on the TMO network, and supplying DMO communications to the firefighters who may have signal trouble inside of a building. The firefighter uses DMO to talk to a radio in the firetruck, and that radio passes the signal onto the TMO network.

Gateways may also refer to a computer device, such as an Application Gateway, that will allow a TETRA network to interact with a foreign computer system, such as an email server.