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How to use same PRI line for both incoming and outbound IVR application

What is a PRI Line ?

A PRI line can be defined as a service level telecommunication standard used for multiple voice channels between two exchanges. It is based on T-carrier ( T1) in US and Canada, while it is based on E-Carrier ( E1) lines in Europe and many other countries. In E1, it has voice channels which means 30 simultensous voice calls while T1 has 24 voice calls.

This is digital communication and normal Telephone Instrument can not be used to make or receive voice calls. A PRI Interface card ( Or digital CTI boards) is required to terminate a PRI line in the PBX.

It has advantage as a single pair of cables carry 30 voice channels which is equivalent of having 30 phone connections. From IVR point of view, since it is a digital technology, it offers many advantages like fast connect/disconnect of voice calls, accurate Caller ID detection, call patching and many others.

But normally, it requires high end CTI boards which are costlier and also PRI lines are not available at many smaller cities.

So, for a IVR hosting company, utilizing a PRI line for both incoming and outbound IVR application is a requirement.

In hosted IVR service, same PRI line can used both for incoming and outgoing IVR applications. Apart from some hosted IVR Service like Bulk Voice Messaging, High Volume Missed Call, one PRI channel could be utilised for multiple IVR application which increase utilization of resources.

While, it is easy to schedule or control the channel allocation in the PRI line, it may not be possible for incoming calls. It is completely dependent on the switch or exchange on which channel out of the 30 channels, would land for the next incoming call. Most switches send incoming voice calls in Round Robin Format, while some exchanges send the voice call to next free channel.

So, some problem may occur when a channel designated channel for outbound dialing gets an incoming call if proper care is not taken. While there are many ways to tackle such problem, one easy way is to inform switch that a particular channel is not available for incoming calls!

While using Global Call Protocol for Dialogic Boards, easy way to inform the switch of exchange about non availability of channel for incoming call is to issue a command gc_SetChanState() with Out Of Service channel state!

So, using this, one can avoid receiving incoming calls on selected voice channels in a PRI line. With this, it becomes much easier for managing both incoming and outgoing IVR application in a single PRI line.

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