> 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/telecom-references/sip-and-voip/voip-redundancy.md).

# Voip Redundancy

Redundancy of both RTP and SIP can be achieved by configuring one [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) (Network Access Point) per VoIP interface for a specific remote proxy.

![VoIP Redundancy Topology](https://docs.telcobridges.com/w/images/c/ce/VoIP_Redundancy_0.png)

### Signaling Redundancy

In the above example, we have configured two [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) Network Access Point that reaches the same SIP destination.  In the event the ethernet interface VOIP0 went down, the ***NAP A*** would become unavailable, and thus routing would take place using ***NAP A***'.

### Media Redundancy

The [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) is also associated to the media by assigning an UDP port range for the RTP.  When [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) is unavailable at the signaling level, the assigned RTP ports aren't being used either.  In the above example, if the ***NAP A*** signaling is down, then all new outgoing calls would then be using VOIP1 ethernet interface for RTP.

### Routing

To enable redundancy, we have to instruct the routing engine about the alternate route. This accomplish by creating a route for a specific destination using ***NAP A***, and another route, for the exact same destination using ***NAP A***'.

All routes using unavailable [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md)s are ignored when routing takes place. So if ***NAP A*** is not available, then the route using ***NAP A***' will be used to route the call to the specific destination.

[NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) availability is a feature of [Scriptable Routing Engine](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/concepts/scriptable-routing-engine/README.md).

### NAP

On the VoIP side, we normally have one [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md) per remote sip proxy. On a configuration where VoIP redundancy is used, we have two [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md)s, one for each VoIP ethernet interface.

### Routes

Since the number of [NAP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/protocols/nap/README.md)s is double for a peer SIP proxy, then the number of routes mays also be doubled.


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