---
title: 'SIP carriers'
summary: 'A SIP carrier is the connection between your PBX and the public telephone network. Also called a SIP trunk - the credentials and server address your PBX uses to place outbound calls and receive inbound ones.'
section: features
tags:
  - crud
  - telephony
  - infrastructure
updated: '2026-06-17'
---

> 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](phone_numbers.md) so a single-carrier blip does not break inbound service.

## See also

- [Phone numbers](phone_numbers.md) - each number has a default and fallback carrier.
- [Route outgoing calls](route_outgoing_calls.md) - rules that dispatch outbound traffic to specific carriers.

```yaml fields
name:
  label: Name
  tab: General
  hint: 'A descriptive name for this SIP carrier (for example, "Primary Provider" or "Backup Line"). No functional effect.'
sip_user:
  label: 'SIP user'
  tab: General
  hint: 'The SIP username used for authentication with the carrier. Supplied by the provider.'
sip_pwd:
  label: 'SIP password'
  tab: General
  hint: 'The SIP password used for authentication. Leave empty when editing to keep the current password unchanged. The reveal is audit-logged.'
sip_registrar:
  label: 'SIP registrar'
  tab: General
  hint: "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."
destination_header:
  label: 'SIP header for outgoing calls'
  tab: General
  hint: '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.'
incoming_header:
  label: 'SIP header for incoming calls'
  tab: General
  hint: '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:
  label: 'DTMF mode'
  tab: General
  hint: '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:
  label: Register
  tab: General
  hint: "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."
```