---
title: "Rhino TAS app: User-Defined Routing"
description: "This application provides operators with a service to allow their subscribers to select their preferred long-distance or international carrier for their out-bound calls. In some countries providing this capability is mandatory, regulatory requirement. Sometimes called: Carrier Pre-selection."
image: https://www.metaswitch.com/hubfs/Charts-Diagrams/rhino-tas-app-user-defined-routing.png
---

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# Rhino TAS app: User-Defined Routing

### Topics

- [Mobile](https://www.metaswitch.com/knowledge-center/reference/topic/mobile),
- [Rhino TAS](https://www.metaswitch.com/knowledge-center/reference/topic/rhino-tas),
- [Rhino TAS apps](https://www.metaswitch.com/knowledge-center/reference/topic/rhino-tas-apps)

### Developed by a Rhino TAS customer.

This application provides operators with a service to allow their subscribers to select their preferred long-distance or international carrier for their out-bound calls. In some countries providing this capability is mandatory, regulatory requirement. Sometimes called: Carrier Pre-selection.

![rhino-tas-app-user-defined-routing](https://www.metaswitch.com/hs-fs/hubfs/Charts-Diagrams/rhino-tas-app-user-defined-routing.png?width=1629&name=rhino-tas-app-user-defined-routing.png)

There are two options in using this service.

- The user pre-defines their preferred long-distance/international carrier and this is saved into a database for their originating number, Then, when calls are made, their pre-selected carrier is used. 
- The subscriber selects the desired carrier on a call by call basis. In which case, they do this adding a prefix to the dialled number for their outbound call. If the prefix is not added then a default carrier is selected – however, where selection is mandatory IVR interaction may be employed to enable subscribers to re-dial the number with the prefix, simply enter the prefix they want or to select the carrier from a list.

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