# Outbound Dial Pattern

Every outbound route uses a dial pattern to decide which numbers it will carry and how those numbers are reshaped before they reach the carrier. This page explains the three parts of a dial pattern and how the related Prefix setting fits in.

## Parts of a dial pattern

A dial pattern is built from three fields: **Pattern**, **Strip**, and **Prepend**.

### Pattern

**Pattern** is required. It sets the rule that a dialed number must satisfy for the route to handle the call.

You can enter a complete number, or use the special characters below to match a group of numbers rather than a single one.

| Character | Matches |
|-----------|---------|
| `X` | Any single digit, 0 through 9. |
| `Z` | Any single digit, 1 through 9. |
| `N` | Any single digit, 2 through 9. |
| `[###]` | Any one of the digits listed inside the brackets. For example, `[123]` matches 1, 2, or 3. |
| `.` | One or more digits that follow the fixed part of the pattern. For example, `9011.` matches any number that begins with 9011 and has at least one more digit, so 9011 on its own does not match. |
| `!` | One or more characters. For example, `9011!` matches any number that begins with 9011, including 9011 itself. |

:::note
Inside brackets you can express a range with a dash. For example, `[136-8]` matches 1, 3, 6, 7, or 8.
:::

:::caution
A pattern that is too broad, such as a bare `.` or `!`, matches far more numbers than you probably intend, including international and premium-rate numbers. Keep each pattern as narrow as the calls the route is meant to carry. Overly permissive patterns are a common toll-fraud exposure.
:::

### Strip

**Strip** is optional. It sets how many digits are removed from the front of the dialed number once that number matches the **Pattern**.

For example, suppose you set **Pattern** to `9.` and **Strip** to `1`. To reach 1588902923, a user dials 91588902923. The system removes the leading 9 and places the call to 1588902923.

:::note
- Stripping happens before the number is handed to the carrier.
- When both **Strip** and **Prepend** are set, the system strips the leading digits first, then adds the prepended digits.
:::

### Prepend

**Prepend** is optional. It sets the digits added to the front of a dialed number once that number matches the **Pattern**.

For example, 202 is the area code for Washington, D.C. If users frequently call that city, set **Prepend** to `202`. A user who wants to reach 2025553097 then only needs to dial 5553097.

:::note
- Prepending happens before the number is handed to the carrier.
- When both **Strip** and **Prepend** are set, the system strips the leading digits first, then adds the prepended digits.
:::

## Prefix and dial patterns

A prefix is a digit that the system removes from a dialed number before passing it to the carrier. You set the prefix to line up with the dial pattern on the outbound route that will carry the call.

:::caution
If the prefix does not match the route's dial pattern, calls to that external number fail. After you change a prefix, or change the route's **Strip** or **Pattern**, place one test call to confirm the number still connects.
:::

### Where the Prefix setting appears

You are asked for a Prefix when you configure:

- A mobile number for a notification contact.

  ![Prefix field on a notification contact's mobile number](/images/pbx/prefix-notification-contacts.png)

- An external number reached when a caller presses a key in an IVR (Interactive Voice Response) menu, the automated menu that greets callers and routes them by keypress.

  ![Prefix field on an external number for an IVR key](/images/pbx/prefix-ivr-external-number.png)

### How to set the prefix

Match the prefix to how the outbound route strips digits.

1. **Leave the Prefix blank.** When the route's **Strip** value is not set, you do not add anything ahead of the number.

   In the example below, only destination numbers that begin with `1` can leave through this route. To call 125451, dial 125451 as is.

   ![Outbound route pattern that matches numbers beginning with 1 and strips nothing](/images/pbx/strip-example1.png)

2. **Add a prefix before the number.** When the route has a **Strip** value, add a prefix that satisfies the **Pattern**.

   In the example below, you add the prefix `9`, and the destination number must begin with `1`. To call 125451, dial 9125451.

   ![Outbound route pattern that requires a leading 9 and strips it before dialing](/images/pbx/strip-example2.png)