Vidicode designed a special Pass Through mode for ISDN lines. Our Call Recorders and Fax Servers for ISDN are connected between the incoming network and the local telephone system, usually a PBX. These devices add new functionality to the line and at the same time leave the existing functionality untouched.

ISDN; Some basic knowledge.

Modern ISDN has 4 wires; 2 wires for receiving data and 2 wires for transmitting data. There are two types of ISDN lines. Basic Rate (BRI) and Primary Rate (PRI). Basic Rate is made to carry only 2 calls with call control. So, 2 channels for voice data and 1 channel for call control. Primary Rate is made to carry up to 30 calls with call control. (24 in the USA). Primary rate is always point-to-point while Basic rate can be point-to-point or point-to-multipoint.

Pass Through mode

Our ISDN devices can be connected to an ISDN line in Pass Through mode. They are connected between the network and the PBX. This means that all these devices must have an IN and an OUT connection. On one side, towards the public network, they must emulate a PBX and on the other side, towards the PBX, they must emulate the public network.

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Call Recorder

The Call Recorder in Pass Through mode has some more freatures besides storing recordings. It can insert a notification message into the conversation. Secondly it can do record on demand, by using DTMF codes from the PBX side. The third trick is the number filter; the numbers send out by the PBX can be hidden to the rest of the world. In the case of the Call Recorder, the line is almost left untouched. Some small modifications are made in the data stream, only when this is needed.

Fax Server & Voice Server

As said before the Fax Server and Voice Server are always operating in Pass Through mode. They both have more influence on the line. They take control over the line at any time. Default, just out of the box, both servers will just pass all the data. After programming an internal number list, they start monitoring the line. If an incoming call arrives with a number that matches the list, the Fax Server takes that call and starts receiving a fax.

The Voice Server takes the call and some other programmed action is initiated, such as entering a voice selection menu, entering a call queue or playing a message and recording a voice mail. The PBX has no knowledge of these actions, because te call is handled by the Fax- or Voice server alone and not passed through.

The Fax Server can initiate outgoing calls by itself when sending faxes. A free line or channel is chosen and the fax is sent. The Voice Server can also initiate calls. This is done when transferring calls to the PBX. Moreover, the Voice Server can also receive commands from the PBX side that initiate action.

Both the Fax Server and Voice Server are capable of handling the ISDN line in Stand Alone mode. This means that a PBX behind the server is not necessary. The line is completely handled by the Fax or Voice Server. A PRI Voice Server can handle up to 30 answering machines with voice mail in a single box.