# Create a SIP Account Trunk

A SIP (Session Initiation Protocol) account trunk lets a third-party device or application register directly to Cloud Voice, much like an extension does. SIP is the signaling protocol that sets up and tears down voice calls. Once the far end registers, the two systems are joined and can pass calls between each other. You would set this up when you need to link another phone system, a SIP-capable server, or a third-party application to Cloud Voice. This page walks you through adding a SIP account trunk from the PBX (Private Branch Exchange, your phone system) web portal.

## Before you begin

- Confirm that no extension number is used on both systems at once. Duplicate numbers on either side of the connection will stop the trunk from routing calls correctly.
- Make sure your account has permission to add trunks.

:::note
If the **Add** button under **Extension and Trunk > Trunk** is greyed out, your account does not have permission to create trunks. Ask your service provider to grant it.
:::

## Create the trunk

1. Sign in to the PBX web portal and go to **Extension and Trunk > Trunk**, then click **Add**.

2. Under **Basic**, fill in these fields:
   - **Name**: A label that helps you recognize the trunk later.
   - **Trunk Status**: Set to **Enabled**.
   - **Select ITSP Template**: Choose **General**. (ITSP stands for Internet Telephony Service Provider. The **General** template applies neutral defaults that suit a direct device-to-device connection.)

3. Under **Detailed Configuration**, set the values below.

   :::note
   The default SIP values are fine to keep. Change them only if your setup requires it.
   :::

   | Setting | What to enter |
   | --- | --- |
   | Trunk Type | Select **Account Trunk**. |
   | Transport | Pick the protocol that carries the SIP signaling: **UDP** (User Datagram Protocol, the common default), **TCP** (Transmission Control Protocol), or **TLS** (Transport Layer Security, which encrypts the signaling). |
   | Username | A username for the SIP account. |
   | Password | A password for the SIP account. |
   | Authentication Name | Keep the generated name or type your own. |

   :::tip
   Give the account a long, random password. This trunk can carry outbound calls, so weak credentials are a common route for toll fraud (unauthorized calls billed to you).
   :::

   :::caution
   The SIP TCP port is turned off by default. If you choose **TCP**, go to **PBX Settings > SIP Settings > General > Basic**, turn on **SIP TCP Port**, then reboot the PBX. The setting only takes effect after the reboot, and a reboot drops every call in progress, so schedule it during a maintenance window.
   :::

   :::note
   If the device you are connecting does not have an **Authentication Name** field, enable **Use User Name as Account Trunk's Authentication Name** instead.
   :::

4. Optional: Open **Advanced**, **Inbound Caller ID Reformatting**, **Outbound Caller ID**, or **SIP Headers** to adjust additional options.

5. Click **Save**, then **Apply**.

## After you finish

- Register the trunk on the third-party software or device. You will need:
  - The SIP account trunk details (username, password, and authentication name).
  - The domain name of your PBX.
  - The SIP registration port. Cloud Voice uses **5060** by default.
- To take inbound calls over the trunk, assign it to at least one inbound route. See [Set up an Inbound Route](/pbx/administrator-guide/set-up-an-inbound-route/).
- To place outbound calls over the trunk, assign it to at least one outbound route. See [Set up an Outbound Route](/pbx/administrator-guide/set-up-an-outbound-route/).

:::caution
The username, password, authentication name, and transport you enter on the third-party device must match the trunk exactly. If any value differs, the device will fail to register and the trunk will stay offline.
:::

## Check the result

Return to **Extension and Trunk > Trunk** and look at the trunk list.

When the trunk has successfully registered from the third-party software or device, its status shows ![Registered trunk status indicator](/images/pbx/trunk-ok.png), confirming that the two systems are connected.

For an explanation of the other trunk states, see [SIP Trunk status](/pbx/administrator-guide/sip-trunk-overview/#concept_kzd_png_tdb__section_b1z_1ft_wpb).