Speech Direction Control (Zenitel Connect Pro)
From Zenitel Wiki
By default, two‑way calls in Zenitel Connect Pro operate in open duplex mode, allowing natural, hands‑free communication for both parties.
In some applications, calls must be established in simplex mode, where audio is restricted to one direction at a time. This mode is often required in control room environments — for example, in prisons, where communication between cells and a guard station must remain operator‑controlled.
When Speech Direction Control is enabled on a device, the initial audio direction is set from the device toward the operator. To speak back, the operator must press the M‑key (Push‑to‑Talk). On ITSV phones, the “*” key performs the same function.
When the operator releases the M‑key (or presses “#” on an ITSV phone), the audio direction returns to being locked from the device.
The operator can switch the call to open duplex mode at any time by pressing “0”.
Configuration
Navigate to Devices and Connections > Configuration. Select the Device and click 
Under "Speech Direction Control" enable Simplex - Remote Press to Talk.
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| Initial speech direction will be from number 102 "Cell B4" |
Optional Setting: Start in Duplex
- Disabled (default):
- The conversation starts in Push‑to‑Talk (simplex) mode.
- Enabled:
- The conversation starts in open duplex mode.
- If the operator presses the M‑key, the conversation switches to Push‑to‑Talk mode and remains in that mode.
"Remote Push‑to‑Talk" between two devices
When two devices configured with Simplex - Remote Press‑to‑Talk (PTT) call each other, both devices start in listen mode, meaning no audio is transmitted in either direction.
Either party may press the PTT key to speak to the other device.
However, if both users press their PTT keys at the same time, both devices enter talk mode simultaneously, and no audio will be exchanged.