> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/tmedia-documentation/configuration/setting-cas-back-digits-variable.md).

# Setting CAS BACK DIGITS Variable

> **Applies to:** Tmedia 3.0, 3.2, 3.3

Once the CAS stack and script are created, you must set the backward digits string to instruct the stack about the sequence of tone requests that has to be sent when acting as the backward end. Refer to [CAS R2 BACK DIGITS](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/cas-r2-back-digits/README.md) for more details. There are two methods to configure the backward digits string.

### Method 1: Setting script BACK DIGITS variable

The backward digits string can be configured directly inside a CAS R2 script. This means that all CAS stacks using the script will benefit from the same configuration.

1- Click \*\*CAS \*\* in the navigation panel

![CASR2 0 A](https://docs.telcobridges.com/w/images/b/b8/CASR2_0_A.png)

2- Click the **Scripts** tab

![CASR2 1 A](https://docs.telcobridges.com/w/images/c/ce/CASR2_1_A.png)

3- Select the desired configuration

![CAS Back 0](https://docs.telcobridges.com/w/images/b/ba/CAS_Back_0.png%E2%80%8E)

4- Edit the "**BACK\_DIGITS**" variable value to the desired value. Refer to [CAS R2 BACK DIGITS](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/cas-r2-back-digits/README.md) for a description of valid digits.

![CAS Back 1](https://docs.telcobridges.com/w/images/4/47/CAS_Back_1.png%E2%80%8E)

### Method 2: Setting stack BACK DIGITS variable

The backward digits string can also be overwritten on a per E1/CAS R2 stack base.

1- Click **CAS** in the navigation panel

![CASR2 0 A](https://docs.telcobridges.com/w/images/b/b8/CASR2_0_A.png)

2- Select the desired CAS stack

![CAS Back 0](https://docs.telcobridges.com/w/images/5/57/CAS_Back_0.png%E2%80%8E%E2%80%8E)

3- Click **Variant Script Variables** to expand area

![CAS Back 2](https://docs.telcobridges.com/w/images/c/c2/CAS_Back_2.png%E2%80%8E)

4- Select the **BACK\_DIGITS** variable and enter the desired value

![CAS Back 3](https://docs.telcobridges.com/w/images/7/72/CAS_Back_3.png%E2%80%8E)

**Path**

```
/configurations/@[configuration_name]/cas_scripts/@[script_name]
```

**Parameters (text)**

```
/configurations/@[configuration_name]/cas_scripts/@[script_name]
name        = "@[script_name]"
revision    = 128082
source      = ""
```

**Parameters (json)**

```
  "name" : "@[script_name]",
  "revision" : 128082,
  "source" : "",
  "unique_name" : "@[script_name]"
}
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://prosbcdocs.telcobridges.com/tmedia-documentation/configuration/setting-cas-back-digits-variable.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.