TETRA supports two call modes -- a Trunked Mode, where radio towers and base stations are involved, and a Direct Mode, where radios talk among each other on a simplex frequency. Trunked mode allows for all of the TETRA features to work smoothly within the coverage area. Most radio operations will operate within this mode. Direct Mode, on the other hand, is designed for areas outside of the trunking coverage, or for cases where the radio group wishes to be isolated from other conversations.
TETRA networks support a variety of call types. Traditional half-duplex group calls are available, where one person talks, and a group of people listen. TETRA also offers individual calls, in either full or half duplex, allow for personal / private communications using the same radio. Yes, you may make a radio to radio call with TETRA, and use the radios like telephones! Speaking of telephones, TETRA easily interconnects into VoIP telephone solutions using the standard SIP protocol, allowing a user to operate the radio like a telephone, including the natural full-duplex nature of talking and listening in real time, just like a telephone. TETRA has an internal priority system, and an emergency call has the ability to manage a busy system, displacing a normal call to allow the emergency call resources. If there is an emergency, the system will make room for that call to be heard!
TETRA supports two special modes that help extend communications to the last mile. Gateway Mode is when a mobile radio acts as a "bridge" between a trunk radio system, and a direct mode radio group. For example, a gateway may be located inside of a service vehicle. Portable radios may switch to direct mode, and talk through the radio in the service vehicle back to the main trunking network. This particularly helps inbuilding coverage, or where workers may need to be connected near electrically noisy equipment, where the trunk system might not provide sufficient signal strength. Repeater mode is used outside of a trunk environment to allow several radios to participate in a conversation. A centrally located radio may be used to ensure all of the operaters hear each other. Please see the graphics along the right side of the page for visual descriptions of these two modes.
|Gateway Operation||Repeater Operation|
|Priority Calls||TETRA systems have levels of priority, so that a busy system will make room for a supervisor call, and/or emergency calls.|
|SDS Messages||Short Data Service -- these are small text messages sent to either individuals, or groups. There are forms of SDS messages that may be sent to machines, such as a radio wired to a door, commanding it to open.|
|Status Messages||Pre-defined SDS messages that are common to users, such as "arrived on scene", or "going to lunch", or "off duty".|
TETRA supports a very efficient GPS algorithm for Automated Vehicle Location tracking. Often transmitting on the control channel, GPS information may be sent to mapping programs without getting in the way of voice communications.
|Some radios may detect if they are moving, implying that the worker is moving around on duty. If motion stops, the radio may alarm the group, on the assumption that the worker has fallen down, or in trouble.|
|Late Entry||If a conversation is ongoing, and a worker turns their radio on, the radio will detect that it needs to join the conversation.|
|Encryption||TETRA supports Air Interface Encryption (AIE) at 30 bits of strength, or complete End to End (E2E) 128 bit AES encryption.|
|Security||TETRA's infrastructure may be configured to prevent a radio from joining the network. Other radios are available that they may be disabled with an over the air command.|
|Many TETRA radios have a display on them that may be interactively used by the operator. Small applications may be written, such as a job ticket system, that a dispatcher may send written instructions to the radio, and the operator reads them. Once the task is complete, the operator may use the radio to transmit a competion back to the dispatcher, complete with a GPS tag and datestamp.|
|Dual Head Radios||Some work vehicles, such as a fire truck, have two sensible places for radio operations. Some radio manufacturers offer dual heads, allowing one radio body to be controlled from two different locations.|
TETRA radios are aware of how much power is required to communicate with the trunked radio system. If lower TX power levels will work, the radios will back off the transmitter power, allowing for longer battery life.
|Dynamic Groups||The TETRA Dispatcher is a special console-driven user with advanced authority to create talkgroups on the fly. Using software on the TETRA network, the dispatch user may select a group of people, and instantly create a talkgroup for them. The radios are programmed in real-time, and the users may start talking immediately afterwards. Upon completion of the activity, the dispatcher may easily disband the talkgroup, returning the affected radios back to normal operation.|