How VICIdial handles bridging, transfers, and SIP calls
Understand VICIdial's bridging approach to SIP calls, why it rejects PSTN bridges, and how to configure your integration for IP-authenticated SIP URIs.
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When integrating with VICIdial, it's important to understand how its SIP call flow works. VICIdial uses a bridging approach for connecting calls rather than true SIP transfers.
Key behaviors
Bridging instead of transfers
VICIdial creates a conference bridge (a 3-way call) to connect parties. It does not perform a true SIP call transfer.
Result: The VICIdial server remains in the media path as a B2BUA (Back-to-Back User Agent) between all parties on the call.
Note: If you're troubleshooting, you won't see your server's number directly when interacting with the agent—all signaling and media go through VICIdial.
Rejects PSTN bridges
VICIdial will reject attempts to bridge calls out to external phone numbers (PSTN).
- It typically returns a SIP 603 Decline response.
- This is usually due to a policy restriction, not a technical limitation—many setups block external bridging for security or billing reasons.
Requires SIP URI destinations
VICIdial only accepts calls to SIP URIs within its trusted network.
- Authentication: Your server's IP address must be whitelisted on their side.
- It will only allow calls to SIP endpoints that are reachable using IP authentication, not username/password credentials.
What this means for you
When designing an integration with VICIdial:
- Expect VICIdial to keep all calls anchored through its servers. The B2BUA architecture means you won't have direct end-to-end connectivity.
- Do not plan to bridge directly out to PSTN or external phone numbers via VICIdial. Route those calls externally through your own trunk if needed.
- Make sure your SIP server is reachable using IP-based auth and is allowed on VICIdial's trusted IP list. Contact your VICIdial administrator to whitelist your LiveKit SIP server IPs.
Summary
| Feature | How VICIdial handles it |
|---|---|
| Call transfers | Uses bridging instead of SIP transfers |
| External PSTN calls | Declines bridging to PSTN (SIP 603) |
| Destinations allowed | SIP URIs only, with IP authentication |
| Media path | VICIdial stays in the media path as B2BUA |
Troubleshooting tips
If calls to external numbers fail with 603 Decline
- Confirm your VICIdial deployment's policy allows external bridging (most don't by default).
- Consider routing PSTN calls through a separate trunk that bypasses VICIdial.
If calls aren't connecting at all
- Verify your server's IP is whitelisted in VICIdial's trusted IP list.
- Check that you're using SIP URI destinations, not PSTN numbers.
- Ensure no firewall is blocking SIP signaling or RTP media between your server and VICIdial.
If you need caller ID or call context
- Since VICIdial acts as a B2BUA, inspect the SIP headers it forwards—some may be rewritten or stripped.
- Work with your VICIdial administrator to configure header pass-through if needed.