Calls & audio

How voice travels between Customer SIP and GSM on the phone.

Outbound call flow

For a typical termination call:

1. A Customer switch sends SIP to your tenant’s VMGateServer ingress.
2. VMGateServer applies routing and selects an online VMGateClient and SIM slot.
3. VMGateServer sends a dial instruction to the phone over the VMGate network link.
4. VMGateClient places a normal mobile outbound call on GSM.
5. When the GSM leg connects, audio is bridged in both directions through the USB audio board and VMGateServer.
6. When either side hangs up, VMGateServer tears down the SIP session and the app ends the GSM call.

VMGateClient does not originate production routing on its own — VMGateServer decides which client and number to use.

Audio path

Voice path on the phone:

Customer SIP → VMGateServer → VMGateClient → USB audio board → phone GSM radio → mobile network

Return audio follows the reverse path.

VMGate Audio must be installed and on the same release as VMGateClient (chapters 03 and 07).

The phone’s mobile data or Wi‑Fi carries the link to VMGateServer. The USB board is for call audio only.

GSM behavior

Each assignment is a standard mobile outbound call on the assigned SIM. Multi-SIM phones may receive traffic on SIM 1, SIM 2, or both depending on portal routing and slot enablement.

Incoming GSM handling is under menu → Settings → Incoming GSM calls. The default is Answer locally — VMGateClient shows an Answer / Reject screen on the phone when a GSM call arrives.

Optional settings on the same screen:

• Reject all incoming GSM — every incoming GSM call is declined automatically.
• Prepared audio folder — pick a folder, run Prepare IVR files, then incoming calls can play one of the prepared clips after a short ring. Set a maximum call length if needed.

While an outbound termination call is in progress, new incoming GSM calls are rejected automatically.

Rollout quality checks

Before production traffic, place test calls from your lab Customer trunk to known mobile and landline numbers. Confirm audio both ways and acceptable delay.

If audio fails but GSM connects, check in order:

• USB board seated on the left port and USB permission granted for the device from Startel International
• VMGate Audio installed (chapter 03)
• Menu → Audio diagnostics — board detected, helper running
• Portal status ready, not no_dongle

Persistent one-way audio after the above usually indicates hardware seating or helper/board state — not a routing rule misconfiguration alone.