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. Choose one Layer-1 mode:

• Answer locally (default) — VMGateClient shows Answer / Reject on the phone when a GSM call arrives. Portal inbound IVR / Forward dialpeers are not used.
• Forward to server — the phone answers under server control. Portal Layer-2 (IVR / Forward / Reject on the SIM slot) applies. Configure that in the VMGateServer manual chapter 15 and slot policy (portal chapter 05).
• Reject all incoming GSM — every incoming GSM call is declined automatically on the handset.

Optional on the same screen when answering locally:

• 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. This is local handset audio — separate from portal IVR profiles under Inbound GSM.

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.

SMS path

Outbound SMS follows a parallel path to voice: the Customer’s switch connects to your tenant’s SMS ingress, VMGateServer routes the message, and the selected VMGateClient sends it on the GSM SIM. Delivery reports (when the network provides them) are shown in portal SMS History.

During an outbound GSM call: SMS is still accepted. The slot that is on the call can send immediately. The other enabled slot queues until the call ends or the SMS send timeout is reached — whichever comes first. (Same rule as chapter 05.)

The USB audio board is for voice bridging. SMS uses the phone’s modem; you do not need the dongle solely to send SMS, but production sites usually keep the board connected for calls.