# SIP trunk

> Connect a third-party PBX, provider, voice AI platform or Microsoft Teams to your call flow.

- URL: https://kb.voipcloud.online/pbx/accept-make-divert/sip-trunk/
- Section: PBX › Accept, make and divert calls
- Type: reference
- Applies to: All countries
- PBX object: sip_trunk
- Last reviewed: 2026-11-09

**SIP trunk** connects your PBX to another phone system: your own on-premises or hosted PBX, another provider, a voice AI platform, or Microsoft Teams. Calls can flow both ways.

## Before you start

You need an unassigned **trunk licence** and enough **channels**, ordered in **Services** › **SIP trunking**. Each channel carries one call at a time in either direction, so 5 channels allow 5 simultaneous calls. If all your trunk licences are already used by other SIP trunk objects, order another one first.

**On a free trial?** Free trial accounts can have up to 5 SIP trunk channels, trial calls end after 1 minute, and only your own hosted numbers can be used as caller ID. See [Your free trial](https://kb.voipcloud.online/getting-started/free-trial/).

## Add it to your call flow

1. Drag **SIP trunk** from the **Accept, make and divert calls** group onto the canvas and click the gear icon.
2. Enter a **Name**, set the **Number of channels** and choose the **Mode**.
3. Fill in the **Mode configuration** for the mode you chose (see below).
4. Click **Save**.
5. To send calls to the trunk, connect an [Inbound number](https://kb.voipcloud.online/pbx/receive-calls/inbound-number/) or another object to it.
6. Click **Apply configuration**.

## Common settings

| Setting | What it does |
| --- | --- |
| Name | Label on the canvas. |
| Number of channels | How many calls can use the trunk at the same time. |
| Notification email (optional) | Get an email when the channel limit is reached. |
| Mode | **SIP registration**, **IP authentication** or **Microsoft Teams gateway**. |

## SIP registration

Use this when your other PBX signs in to this PBX with a username and password. Your PBX can then call users here and dial out, and users here can call extensions on your PBX.

![SIP trunk in SIP registration mode, with the credentials blurred](https://kb.voipcloud.online/images/pbx/accept-make-divert/sip-trunk-sip-registration.webp)

| Setting | What it does |
| --- | --- |
| SIP credentials | The **Domain**, **Username** and **Password** to enter in your other PBX. Use **Generate a new password** to change the password; you'll need to update your PBX afterwards. |
| Transport protocol | The protocol your PBX must use to connect: TCP, or TLS if TLS encryption is turned on in **Settings** › **General**. With TLS, **Media encryption** shows SRTP. |
| Supported audio codecs | Opus, G.722, G.711 A-law and G.711 u-law. |
| Status | Whether your PBX is connected (**Online** or **Offline**). |
| Check IP address for blocking | A device that tries to register with wrong credentials is blocked, and the block lifts after 5 minutes. Enter an IP address to check whether it's blocked. |
| SIP trunk call plan | Rates for outgoing calls through the trunk. Without a call plan, outgoing calls won't work. |
| Caller ID | The number shown for outgoing calls. **Keep originator's caller ID** passes through the number your PBX sends; if there's none, the call is anonymous. |
| Ring time, seconds | How long to try the trunk before the call takes the **No answer** path. |
| Allow connection from one IP address only | Locks the trunk to your PBX's public IP address, for extra security. |
| Inbound rules | Under **Advanced parameters**. For phone numbers hosted on the other PBX that pass through this PBX: turn on **Route all remote PBX phone numbers via this SIP trunk**, or click **Add phone numbers** to add them one by one. |
| Outbound rules | Under **Advanced parameters**. Click **Add internal numbers** to add internal numbers hosted on the other PBX, so users here can call them. |

## IP authentication

Use this to send calls to a remote server that recognises this PBX by its IP address. When a call reaches the object, it's forwarded to the **SIP URI address** you enter.

![SIP trunk in IP authentication mode](https://kb.voipcloud.online/images/pbx/accept-make-divert/sip-trunk-ip-authentication.webp)

| Setting | What it does |
| --- | --- |
| Domain | This PBX's address, to allow on the remote server. It resolves to several IP addresses that can change, so the remote server must accept calls from all of them. |
| SIP URI address | Where calls are sent. Format: `<remote_number>@<remote_server>:<port>` or `<remote_server>:<port>`, for example `61399997999@sipserver.com:5060` or `111.22.33.44:5060`. |
| Ring time, seconds | How long to wait for an answer before the call takes the **No answer** path. |

## Microsoft Teams gateway

Use this to connect Microsoft Teams with direct routing. Set up the integration in **Services** › **Microsoft Teams** first.

![SIP trunk in Microsoft Teams gateway mode](https://kb.voipcloud.online/images/pbx/accept-make-divert/sip-trunk-teams-gateway.webp)

| Setting | What it does |
| --- | --- |
| SIP trunk call plan | Rates for outgoing calls from Teams. |
| Caller ID | The number shown for outgoing calls, or **Anonymous**. |
| Ring time, seconds | How long to ring Teams before giving up. |
| Add Microsoft Teams account | The Teams accounts this trunk connects to. |

## Call paths

| Path | When it's used |
| --- | --- |
| **Failed** | The call couldn't be delivered to the remote server. |
| **No answer** | The ring time ran out. |
| **Remote PBX phone numbers routing** | Only when **Route all remote PBX phone numbers via this SIP trunk** is on. |

In **Microsoft Teams gateway** mode the object has no outgoing paths: Teams handles the call. In the other modes, if **Failed** or **No answer** isn't connected, the call ends.

## Related

- [How the PBX works](https://kb.voipcloud.online/pbx/basics/pbx-overview/)
- [Inbound number](https://kb.voipcloud.online/pbx/receive-calls/inbound-number/)