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SIP carriers

A SIP carrier is the connection between your PBX and the public telephone network. Also called a SIP trunk in telephony jargon. Without at least one configured carrier, the PBX cannot reach the outside world.

Overview

A SIP carrier holds the credentials and server address your PBX uses to place outbound calls and receive inbound ones. Most tenants run two carriers, a primary and a fallback that takes over automatically if the primary loses connectivity.

What it does

To receive inbound calls, the PBX registers with the carrier (a SIP REGISTER packet carrying the credentials), so the carrier knows where to deliver them.

State What it means
Registered Inbound and outbound calls work normally.
Not registered Inbound calls fail. Outbound may still work if the carrier uses IP-based authentication.

A carrier is invisible to callers when healthy. When it is misconfigured, the symptoms point to the field at fault:

Symptom Likely cause Fix
All inbound calls fail Carrier is not registered Turn on the Register toggle. Verify credentials with the provider.
All outbound calls fail Wrong registrar address or credentials Check SIP user / password / registrar against the provider's onboarding docs.
Outbound calls fail with "destination not found" Wrong destination header Switch SIP header for outgoing calls between Default / P-Called-Party-Id / To.

Set a fallback carrier on every phone number so a single-carrier blip does not break inbound service.

See also

Form fields

Fields available in the create and edit forms.

General

Name

A descriptive name for this SIP carrier (for example, "Primary Provider" or "Backup Line"). No functional effect.

SIP user

The SIP username used for authentication with the carrier. Supplied by the provider.

SIP password

The SIP password used for authentication. Leave empty when editing to keep the current password unchanged. The reveal is audit-logged.

SIP registrar

The hostname or IP address of the provider's SIP server (for example, sip.provider.com). Where the PBX sends REGISTER and outbound INVITE packets.

SIP header for outgoing calls

Which SIP header carries the called number on outbound calls. Options: Default (works for most providers), P-Called-Party-Id (required by some Belgian carriers), To. Wrong setting produces "destination not found" errors on outbound.

SIP header for incoming calls

Which SIP header the PBX reads to determine the dialed number on inbound calls. Options: Request-URI (default, works for most providers), To, Contact. Change only when the carrier delivers the number in a non-standard header.

DTMF mode

How DTMF tones (keypad presses) are sent during a call. Auto lets the PBX negotiate with the carrier. Use RFC4733 or SIP Info when the carrier requires a specific mode, and Inband only as a last resort.

Register

When on, the PBX periodically registers with this carrier's registrar to receive incoming calls. Turn off only when the carrier authenticates via IP allow-list.

Updated