---
title: "Rhino TAS app: Reverse IM-SSF"
description: Reverse IM-SSF enables the existing legacy subscriber base to access the new IMS application-server hosted services.
image: https://www.metaswitch.com/hubfs/Charts-Diagrams/rhino-tas-app-reverse-im-ssf.png
---

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# Rhino TAS app: Reverse IM-SSF

### 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 Metaswitch.

Reverse IM-SSF enables the existing legacy subscriber base to access the new IMS application-server hosted services.

![rhino-tas-app-reverse-im-ssf](https://www.metaswitch.com/hs-fs/hubfs/Charts-Diagrams/rhino-tas-app-reverse-im-ssf.png?width=1326&name=rhino-tas-app-reverse-im-ssf.png)

The roll-out of IMS introduces a new service layer specific to that technology which promises to enable a wealth of new applications. The primary function of Reverse IM-SSF is to do protocol conversion between IN and IMS — so that IN users can use services which are implemented on the IMS.

Although Reverse IM-SSF is not specified in the IMS architecture (whereas IM-SSF is specified), Reverse IM-SSF is equally attractive, as it means that the existing legacy subscriber base — hugely in the majority and likely to remain so for a considerable time — can access the new IMS application server-hosted services. In this way, the operator can maximise the return on the IMS investment.

Network Operator Benefit:

- Reverse IM-SSF enables operators to leverage their investment in IMS applications to stimulate revenue from their legacy (non-IMS) subscriber base.
- Offering legacy customers a rich variety of IMS services can also help with the retention of existing subscribers and the acquisition of new customers.

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