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Voice communication

T.Flex supports the following types voice communication:

  • One-to-many:
    • Group call (from anywhere in the app)
    • Priority call
    • Dynamic group call
    • Group call to PMR over T.Bridge
  • One-to-one:
    • Individual simplex call
    • Direct call
    • Offline call
    • Remote microphone control (ambiance listening mode)
    • E2E encrypted call

For details about emergency calls with GPS location notification, see Emergency calls.

One-to-many communication

Group call

Push-To-Talk (PTT) is the main feature of any radio, from simple walkie-talkie handhelds to professional mobile radios such as MPT, DMR, P25 or TETRA. PTT allows a single person to reach hundreds of users in multiple channels by pushing a button. This time-honored and efficient approach is also implemented in the TASSTA solution to improve communication.

Group/channel setup in T.Flex is similar to PMR terminals. During PTT use, the screen shows appropriate color behavior: light green – red – green, meaning released – requested – granted, respectively.

PTT hold timeout specifics:

Administrative configuration may define a PTT hold timeout for your user account, where you are allowed to hold the floor for no longer than a specified time and PTT is automatically released for you when the time limit is hit. This feature works in some situations but not in others – it is applicable where there is a PTT queue (floor control).
In particular, the timeout works in the following types of call:

  • Group call (except in conference channels)

The timeout does not work in the following situations:

  • Conference channel
  • Individual call

PTT screen

The PTT screen is filled with a single PTT button. This button changes color from light green to green when someone is speaking in your group.

At the bottom, the PTT button may display information about the user that is currently talking in the channel. If the channel is free, it may show the name of the channel and the user that last spoke. That behavior is configured by the administrator in T.Commander.

In addition, the screen shows the names of available audio devices and lets you switch them.

Broadcast call

A broadcast call is similar in purpose to a group call but it is initiated by the broadcast call action instead of the PTT button. Broadcast call permissions are also administered separately from PTT permissions. Broadcast calls are normally intended for announcements and organizational information. In this type of call, the initiator subscribes specific users; these users can only listen and cannot opt out or answer.

To make a broadcast call

  1. Go to the user list by selecting it in the navigation drawer.
  2. Tap the Select users for broadcast call icon Select users for broadcast call icon.
  3. In the view that opens, select the users you need, and tap the same icon again.

PTT is available throughout T.Flex

Channel talk is the central functionality of the TASSTA system. By default, you can start a channel talk from any operational interface using the PTT button. Even if you are focused on the map interface, the PTT button is always at hand. This feature has the advantage of providing easy and fast communication anytime in any context.

Priority call

The priority call is one of the major features of modern professional communication. It allows users with a higher priority to interrupt individual or group call communication at any time and get through with important information. The levels of priority are unlimited in the TASSTA system and can be individually set up for each user in T.Commander.

Dynamic group call

A dynamic group is formed on the spot from selected T.Flex users. A dispatcher assigns a dynamic group to selected users in T.Rodon to create an ad-hoc channel for immediate communication needs. This feature is designed for command and control centers to provide a flexible operational tool for team organization and quick response.

A dynamic group exists until the last T.Flex user leaves the dynamic group call channel.

Multilistening

You can listen to multiple channels at the same time if this functionality is enabled for you by the administrator in T.Commander. If this is the case, enable multilistening for each group you need. Do the following:

  1. In the group list, long-tap the icon to the left of the group. This enables listening for the group, and the icon changes accordingly.
  2. If you long-tap the icon again, this either mutes the group or disables listening for it, depending on administrative configuration.

Groups for which listening is enabled have a green circle icon on the left.

Accidental PTT use can be prevented for specific channels

The administrator can configure a channel so that only deliberate group talk occurs in it. Before you can use PTT in such a channel, you have to select that channel. This starts a timer, and you have to press PTT before the timer runs out; otherwise, you'll need to select the channel again.

Group call to PMR over T.Bridge

Any PMR Network such as TETRA or MOTOTRBO can be extended with the TASSTA solution or become integrated as its complement. Voice communication between PMR and TASSTA is possible through T.Bridge. If T.Bridge is configured in your environment, voice communication involving both networks (TASSTA and PMR) is done through special allocated groups using regular group calls. The T.Bridge configuration is transparent to you as a T.Flex user – use the PTT button and talk, whether your audience is in the TASSTA network or in the PMR network.

One-to-one communication

Individual call

This is the equivalent of a one-to-one simplex call, providing secure point-to-point communication. The two users can be anywhere in the network or in different channels.

To make an individual call

  1. Go to the user list by selecting it in the main menu.
  2. Tap the user you need and then tap the individual call icon. The available action icons are above the user list interface when a user is selected.
  3. Wait for the other user to accept your call, and then use the PTT button to start talking.
What happens during an individual call:

The calling party sees the Outgoing Call window and hears outgoing call ringtones.
The party being called can hear incoming call ringtones and see the incoming call notification.
The calling party has to wait until the call is accepted or drop the call using the red phone button.
The party being called can accept the incoming individual call or drop it using the red phone button.

If the user could not answer the call, they get a notification message about the missed call.

Direct individual call

This is a call to another user without prior notice. The user who receives the call immediately sees the icon of the established connection on the device screen. This type of call does not require confirmation from the receiving party.

To make a direct call

  1. Go to the user list by selecting it in the main menu.
  2. Tap the user you need and then tap the direct call icon. The available action icons are above the user list interface when a user is selected.

If the corresponding parameter is configured by the administrator in T.Commander, a progress bar appears and will run out unless one of the parties involved in the call presses the PTT button. The call is interrupted if the progress bar runs out.

Offline user call

You can initiate an individual call to an offline user. In this case the system automatically accepts the call and records your message. Use the PTT button to record the message. Your records appear in the history and will be available when user is online.

If you get such a call while you are offline, you can listen to the recorded message in the History view, on the Missed calls tab. Tap the play button for that message to play back the recording.

Muting users

You can mute specific users in a similar way to how you disable listening for groups. This doesn't change the muted users' configuration or permissions in any way; it only makes sure you don't hear them in T.Flex.

To mute or unmute a user, long-tap the icon to the left of that user.

E2E encrypted call

T.Flex offers an additional security mechanism called end-to-end encryption (E2EE), implemented on top of built-in TLS. E2EE prevents potential eavesdroppers from being able to access the encrypted conversation even if they manage to intercept the communication channel. E2EE in TASSTA provides a way of communication where only the communicating users with matching key pairs (encryption and decryption keys) can hear the voice messages. It is an additional level of protection to ensure that no third parties without the keys can capture the voice data being transmitted or store it.

When you make an E2EE call, you need both an encryption key and a decryption key. Agree on the keys with the other user in advance. You can also share the keys with other users from the user list or from the map.

Establishing a secure connection

Important:
  • The E2EE feature must be enabled for both participating users by the administrator in T.Commander.
  • For security reasons, all recorded E2EE calls can be played back from the history only if the appropriate keys are provided.
  • Emergency calls and remote listening audio are never E2E encrypted.

Encrypt both devices and share the keys with the user you need. For that, take the following steps:

  1. Make sure Enable PTT Encryption is enabled in T.Flex on both devices.
  2. Come up with a key. Any string can be used as the key. Save it as your encryption key in the settings.
  3. Select the user you need and share the encryption key with them. Instruct the user that they should save it as their decryption key.
  4. Confirm that the other user has accepted and saved the key.
  5. Obtain the other user's key and save it as your decryption key in the settings.

The padlock icon on the PTT button indicates the state of E2EE configuration:

  • Green, closed – encryption is turned on, and at least one of the two keys is set
  • Green, open – encryption is turned off, but at least one of the two keys is set
  • Gray, open – neither of the two keys is set (no matter if encryption is turned on)

To go to the encryption configuration screen, long-tap the padlock icon.

If you clear the Encryption Key and Decryption Key fields and tap Save, this has the effect of turning off encryption on the device.