How Vicidial Handles Bridging, Transfers, and SIP Calls

Overview

When integrating with Vicidial, it’s important to understand how its SIP call flow works. Vicidial uses a bridgingapproach 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:

• Expect Vicidial to keep all calls anchored through its servers.

• Do not plan to bridge directly out to PSTN or external phone numbers via Vicidial — route those externally if needed.

• Make sure your SIP server is reachable using IP-based auth and is allowed on Vicidial’s trusted IP list.

Summary