> 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/other-pages/other/configure-nfas.md).

# Configure NFAS

> **Applies to:** Tmedia 2.6

ISDN-PRI signaling can be configured for your system. To do so, you must create a new ISDN stack.

Integrated Systems Digital Network (ISDN) is a circuit-switched telephone system that integrated voice and data on the same lines. Tmedia and Tdev systems can be configured to provide an ISDN signaling stack on the trunks of one or more units to meet system configuration requirements.

To create a new ISDN stack:

1- Click **ISDN** in the navigation menu, under the Signaling header

![Click ISDN](https://docs.telcobridges.com/w/images/f/f7/Click_ISDN.jpg)

2- Click **Create New ISDN Stack**

![Toolpack v2.5 Create ISDN Stack](https://docs.telcobridges.com/w/images/2/24/Toolpack_v2.5_Create_ISDN_Stack.png)

3- Create the new stack:

**Note:** TelcoBridges offers several ISDN variants, four of which support NFAS. By clicking on 'Create' you confirm the line service and in the case of ISDN variants which support NFAS you are permitted to add additional line services.

* Verify that the box labeled **Enabled** is checked
* Enter a **name** for the new ISDN stack
* Select a **variant** to associate with the stack
* Determine whether the stack will operate on the **user side**, or the **network side**
* Select a **primary D-channel line service**
* Click **Create**

![Creating new stack](https://docs.telcobridges.com/w/images/6/60/Creating_new_stack.jpg)

4- Verify that the **"ISDN stack was successfully created"** message appears

![ISDN stack success](https://docs.telcobridges.com/w/images/5/54/ISDN_stack_success.jpg)

5- Create a backup line:

* Click on the **Available** line on the righthand side of the screen, and select the arrow to add it to the **Current-Line Services**. Up to 20 line services can be added in one NFAS group.
* Select the line service that will be used as a **D-channel** backup by this ISDN stack instance.
* Click **Save**

![Verify ISDN stack](https://docs.telcobridges.com/w/images/e/eb/Verify_ISDN_stack.jpg)

6- Verify that the **"ISDN stack was successfully updated"** message appears, and that the new **trunk** line is listed in the **ISDN Stack List**

![Isdn stack success updated](https://docs.telcobridges.com/w/images/d/de/Isdn_stack_success_updated.jpg)

### List of Parameters

* [Enabled](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/sip#e)
* [Name](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/m3ua#n)
* [Line Service](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/tdm#l)
* [Variant](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/isdn#i)
* [Side](https://prosbcdocs.telcobridges.com/telecom-references/parameter-reference/isdn#s)


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