TASSTA Documentation Center TASSTA Documentation Center More products
Hide table of contents Hide details Search My account

Voice communication

T.Flex supports the following types of voice communication:

  • One-to-many communication:
    • Group call (from anywhere in the app)
    • Broadcast call
    • Priority call
    • Dynamic group call
    • Group call to PMR over T.Bridge
  • One-to-one communication:
    • Individual simplex call
    • Direct call
    • Offline call
    • Remote microphone control (ambience listening mode)
    • E2E encrypted call
  • Many-to-many communication:
    • Full-duplex call
  • Emergency call (with GPS location notification)

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 on 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.

The PTT button changes color from light green to green when someone is speaking in your group.

The PTT button displays 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 can be configured by the administrator in T.Commander.

See also Live video streaming, where PTT works for users invited to video streams.

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)
  • PTV call
  • Broadcast call
  • Emergency call: only after the emergency PTT timeout ends

The timeout does not work in the following situations:

  • Conference channel
  • Full-duplex call
  • Video call
  • Individual call
  • Emergency call: before the emergency PTT timeout ends

Also note that in networks with bridged connections, the timeout never works for bridge users.

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.


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 as follows:

  1. In the group list, tap and hold the group until the context menu opens.
  2. Tap the circle icon to enable listening for the group.

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

Prevent accidental PTT use

This option is intended for blocking the PTT button and protecting users from unwanted access to the channel while performing work. Importantly, the user must hear the conversations in the channel. When the feature is active, the PTT button is locked automatically by a countdown timer.

Timer activation and timer interval settings are configured by the administrator in T.Commander. To unlock PTT, you need to tap the selected channel in the channel list. The countdown timer starts automatically 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 navigation drawer.
  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 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 navigation drawer.
  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.

Video call

Users can exchange video calls in the TASSTA system. During a video call, each of the participants can change the speaker of the output sound, turn on and off the microphone and video camera, and switch between the front and rear camera view.


Make sure that you have a stable Internet connection when placing or receiving video calls. The quality of a video call depends on the contact with the weakest connection.
Video calls are supported on Android 4.4 KitKat and later.

To make a video call

  1. Go to the user list by selecting it in the navigation drawer.
  2. Tap the user you need and then tap the video 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.
Receiving a video call:

When someone video calls you, you see an INCOMING VIDEO CALL screen, where you can accept or decline the call.

PTV call

This is a video call that does not require confirmation from the receiving party. A PTV call is declined if the receiving party is already in a call.

To make a PTV call

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

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.

When the offline user become online, they get a notification about the offline message. To listen to a recorded offline call, tap the call and then tap the down arrow in the right top corner. Finally, tap the play button in the top right corner.

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, select that user, tap the "three dots" icon and select Listening ON/OFF.

Many-to-many communication

Full-duplex call

In a full-duplex call, multiple users can listen and talk at the same time.

To make a full-duplex call

  1. Go to the user list by selecting it in the navigation drawer.
  2. Tap the Select users for full-duplex call icon Select users for full-duplex call icon.
  3. In the view that opens, select the users you need.
  4. Tap the Start full-duplex call icon Start full-duplex call icon or Start direct full-duplex call icon Start direct full-duplex call icon. If you choose the direct full-duplex call option, the recipients are not prompted to accept the call.

Inactivity timeout

Your administrator may configure an inactivity timeout for calls. If this is enabled, you get a progress bar which counts down while the PTT button remains released by all parties involved in the call. The call is interrupted if this progress bar runs out.

Emergency call

The emergency call feature is integrated into any mobile client and can be useful in emergency situations. Emergency calls do not require acceptance by the operator. They get through automatically to allow the user to talk straight away without any delay. This feature is designed for immediate interaction with the operator of a command and control centers (who are normally T.Rodon users). When an emergency call is in progress, T.Flex sounds an appropriate emergency audio signal and gets an emergency message with GPS coordinates (if GPS is enabled on the caller device).


To ensure the correct processing of emergency calls, grant T.Flex all permissions and enable location services, Bluetooth and notifications on the device where T.Flex is used.

The emergency message is highlighted red. All emergency messages contain the reason that caused the emergency, and it is logged in the emergency journal.

There are a variety of situations that qualify as emergencies: simple emergency (SOS) call, any LWP emergency (Periodic Check, Mandown, No Movement, Impact or Fall Detection, Battery Level Warning or Alarm), zone statuses (if a zone is empty, if a user goes in or out, if a user connects or disconnects, if a user stays in the zone for a certain time), and so on.

All emergency messages appear in the emergency journal, which can be enabled or disabled by the administrator in T.Commander, no matter what caused the emergencies. However, only emergency messages from regular emergency calls (made by tapping Emergency Call) are duplicated in the root channel.

When an emergency call is started, T.Rodon can toggle a distress sound on the caller device.

When an emergency call is completed, the user is transferred in the default group predetermined for the user.

There are a few emergency-related options that an administrator may configure for users in T.Commander, listed below. You cannot change these options in T.Flex.

  • Prevent stop emergency

If this is enabled, you cannot stop an emergency call once you have initiated it. To finish the emergency call in this case:

  1. Tap and hold in the screen to suspend the emergency call.
  2. Wait for the T.Rodon operator to confirm the call end. (T.Rodon shows a confirmation prompt that has to be closed.)
  • Mute outgoing emergency

Mutes the sound of the emergency popup that appears when the user sends an emergency.

  • Max emergency volume

Maximizes the volume for an outgoing emergency when the user sends it.

Making emergency calls

You can make an emergency call in the following two ways:

  • By tapping the Emergency symbol on the PTT screen
  • By opening the Emergency tab in the main menu and holding the Emergency symbol

In either case, you get a popup that says "Click to Cancel Emergency Call" and shows a countdown. This helps prevent false emergencies started by mistake. If you tap the popup before the end of the countdown, the emergency call is cancelled. If the countdown completes uninterrupted, the emergency call starts and the emergency message is sent.

If you use a smartphone with dedicated hardware buttons (for example, Sonim XP7), make an emergency call by pressing and holding the hardware emergency button (usually red).


Use emergency calls only for emergency reasons; do not abuse the feature where a direct call would suffice. Emergency calls are intended for users who are in need of urgent assistance. In addition, emergency calls affect the performance of T.Rodon and T.Flex more than other types of call do.
The TASSTA development and marketing teams accept no liability for any loss or damage by malfunction or misuse. Users need to ensure that their emergency calls sent to T.Rodon by T.Flex can be received by the monitoring administrator.
Before production use, do a coverage network test and physical test of the device, including moving it from one site to another. The monitoring administrator must ensure that their supervised users follow very strict operating instructions. The users and the monitoring administrator should be aware that they cannot rely fully and solely on this product to ensure their safety and security; they can only use this product as an auxiliary, supplemental aid to assist them in knowing the user is in need of assistance.

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 require both an encryption key and a decryption key. You will need to exchange keys with the other user.

Establishing a secure connection

  • 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. In the navigation drawer, tap E2EE to open encryption settings.
  2. Select the Enable PTT Encryption option. Instruct the other user to also enable E2EE on their device.
  3. Come up with a key. Any string can be used as the key. Save it as your encryption key in the settings. Do not manually specify the decryption key.
  4. Select the user you need and share the encryption key with them. For that, tap the "three dots" toolbar icon with this user selected, and tap Share key. The key that you share will be used as the decrytion key by the other user.
  5. Confirm that the other user has accepted the key, and instruct that user to share their own key with you.
  6. Accept the other user's key when you get the Share Key popup message. They key that you accepted will be used as your decryption key.

A dark lock icon (to the right of the user name or alias) on the PTT button indicates that encryption is on.

To turn off encryption mode on the device, clear the Enable PTT Encryption option in E2EE settings.

T.Flex mostly uses two Android audio routes: Voice and Music. In some situations, Notifications is also used.

The Voice route is recommended for situations where multiple users can talk at once. In this route, Android audio effects can be applied as long as they are supported by the hardware. These audio effects (Acoustic Echo Canceler, Noise Supressor and Automatic Gain Control) can be turned on and off in T.Flex settings.


Some devices do not have built-in acoustic echo cancelling, and some makers falsely claim that their devices have it.

The Music route does not support audio effects and provides acceptable audio quality only if one user talks at a time. T.Flex does not currently have fallback software acoustic echo cancelling and relies on the Voice route of the system for that functionality.

The Redirect voice to loud speakers option in T.Flex settings controls which route is used for voice communication. The following table lists the configurations enabled by the option's choices.

Option Which outputs are used Volume controls available Loudspeaker use
Never Voice for all voice audio
Music for event signals, unless the Event and Voice in same output is turned on
Voice and Music Loudspeaker off
Define by proximity sensor Voice for all voice audio
Music for event signals, unless the Event and Voice in same output is turned on
Voice and Music Loudspeaker on, but audio switches to the internal speaker when you put the device to your ear
Always when one user talks
(default choice)
Voice for all voice audio
Music for event signals, unless the Event and Voice in same output is turned on
Voice and Music Loudspeaker on when only one user is talking at a time; loudspeaker off otherwise
Always Music for all voice audio
Notifications for event signals, unless the Event and Voice in same output is turned on
Music and Notifications Loudspeaker on

If the phone is paired with a Bluetooth device or a headset is connected to the phone, then voice audio output switches to Voice and the loudspeaker is turned off regardless of the choice in the Redirect voice to loud speakers option. In effect, the Never choice is forced in this case.