# SIP Trunk Overview

A SIP trunk is a virtual phone line delivered by an Internet Telephony Service Provider (ITSP). Once a trunk is connected to Cloud Voice, your users place and answer calls over the internet rather than over traditional analog or digital lines.

## Key terms

**SIP**: Session Initiation Protocol, a signaling protocol defined by the IETF. It operates at the application layer to set up, change, and tear down real-time sessions between one or more parties.

**ITSP**: Internet Telephony Service Provider, a company that sells VoIP (Voice over Internet Protocol) calling service. You may also see these providers called VoIP service providers.

## Trunk types

Cloud Voice works with three kinds of SIP trunk.

### SIP Register Trunk

A registration-based trunk that authenticates to the provider with a username and password.

:::note
A register trunk needs at least one DID (Direct Inward Dialing) number, which is a phone number the provider routes straight to your system.
:::

### SIP Peer Trunk

An IP-based trunk that authenticates using the IP address and port of your PBX (Private Branch Exchange, your phone system) rather than a login. Cloud Voice offers three variants:

- **Peer Trunk (DID Based)**: the provider routes incoming calls by DID number.
- **Peer Trunk (Port Based)**: the provider routes incoming calls by the SIP registration port.
- **Peer Trunk (Private Network)**: for setups where the provider and the PBX sit on the same private network.

:::note
- DID-based peer trunks require at least one DID number.
- You can configure up to five port-based peer trunks.
:::

### SIP Account Trunk

Use this type to link Cloud Voice with another device. Here Cloud Voice takes the role of the VoIP account provider: it supplies an account that the other device registers against to establish the connection.

## Ways to create a trunk

**From a template.** Cloud Voice includes ready-made configuration templates for many established ITSPs, letting you stand up a trunk with minimal setup. See [Create a SIP Trunk from a Template](/pbx/administrator-guide/create-a-sip-trunk-from-a-template/).

:::tip
If your provider has a template, use it. The template fills in most of the technical settings for you, so there is less to configure by hand and less chance of entering a value incorrectly.
:::

**As a general trunk.** If your provider has not been validated against a template, build the trunk manually:

- [Create a SIP Register Trunk](/pbx/administrator-guide/create-a-sip-register-trunk/)
- [Create a SIP Peer Trunk](/pbx/administrator-guide/create-a-sip-peer-trunk/)
- [Create a SIP Account Trunk](/pbx/administrator-guide/create-a-sip-account-trunk/)

## Trunk status icons

Each trunk in Cloud Voice shows a status icon that reflects its current connection state.

| Icon | Meaning |
| --- | --- |
| ![Disabled trunk indicator](/images/pbx/trunk-disabled.png) | Disabled. |
| ![Unregistered trunk indicator](/images/pbx/trunk-unregistered.png) | Unreachable, or registration failed. A failed registration can be caused by an authentication error, a mismatched transport type, or the request being rejected. |
| ![Authentication error indicator](/images/pbx/trunk-authentication-error.png) | Authentication failed. |
| ![Registering trunk indicator](/images/pbx/trunk-registering.png) | Registering. |
| ![Registered trunk indicator](/images/pbx/trunk-ok.png) | Registered. |
| ![Unmonitored trunk indicator](/images/pbx/trunk-unmonitored.png) | Unmonitored. |
| ![Busy trunk indicator](/images/pbx/trunk-busy.png) | Busy, every available channel is in use. |