Specifications

2-26

Reference Guide

Model No.

Running Head

ISDN Primary Rate Interface (PRI) Server Applications

By grooming the PBX and CODEC PRI circuits onto a single, outbound PRI facility, the IAD

utilizes Dynamic Bandwidth Allocation (DBA). The PBX would seize B-channels on a

call-by-call basis, utilizing one B-channel for every call. The Video Codec would request a

pre-determined number of B-channels. For example, if a 384K call was required, the Video

CODEC requests a single 384K circuit, which would consume six of the B-channels. If the

ISDN service supports 384K calls, or Multi-Rate services, and the bandwidth is available, the

ISDN server card will connect the Video CODEC to proper time slots. If the bandwidth is not

available, the IAD rejects the call. If 384K service is not supported by the ISDN service, the

IAD must be equipped with an Inverse Multiplexer (IMUX) server card. The IMUX server

card is capable of bonding or aggregating multiple 64K circuits into a single larger capacity

circuit.

Inbound calls would be handled in a similar manner. All inbound calls would be screened by

the IADs PRI Server card. Calls destined for the PBX would be routed to the PBX, and calls

destined for the Video Conference Unit would be routed there. If the video Codec was in use,

the IAD will inform the ISDN service that the unit was in a busy condition.

A unique feature of the PRI Server card is its ability to combine multiple ISDN circuits to form

a Video Broadcast. This feature is very useful for distance learning applications where a

central site broadcasts video to multiple remote locations. In this application, an IAD equipped

with a PRI server card takes a video source and makes a two-way connection with the first

remote IAD video conference site as shown in Figure 2-15. Once that connection is

established, the host IAD calls up to a total of 32 additional remote video conferences sites

and distributes the same outbound video feed to all of those sites. These additional sites are in

a view-only mode and do not distribute video back to the central site. The loss of one or more

of the remote sites will not affect the broadcast to the other sites. This application can be

upgraded to allow two-way audio to each of the sites though the use of analog voice cards.

Figure 2-15. IAD in Video Broadcast Applications

T1/E1

Backbone

network

Video

T1/E1

IAD