Network; Network Operation; Data Network; Audio Network - ASL INTERCOM VAR8 Product Description

3

Network

3.1

Network Operation

The Intellevac Network enables a number of physically distributed Slave Units to be controlled by a master
Audio Control Unit (ACU).
The units in the Intellevac Network are interconnected by a loop cable, which carries a data ring for control
and a triple audio ring. Both rings are tolerant to open and short circuit faults, and operate over MICC and
other fire rated cables.
Any network fault causes the Audio Control Unit to operate in All Call mode.
A Slave Unit operating in All Call mode due to a processor fault results in a network fault,
thus causing the Audio Control Unit to operate in All Call mode.
3.1.1

Data Network

At each unit, bi-directional RS485 interfaces connect to each side of the ring. This uses one twisted wire pair
in the network cable.
The data ring operates in one preferred direction. In a fault free condition all data originated from the Audio
Control Unit is transmitted from the UPSTREAM port to the DOWNSTREAM port of the first Slave Unit. The
data is then copied through each Slave Unit until it is received back at the Audio Control Unit. Each Slave
Unit replies in the direction from which it receives data.
If an open or short circuit failure occurs, such that the Audio Control Unit fails to see its own transmissions
coming back, it starts to transmit in both directions, UPSTREAM and DOWNSTREAM. This prevents an
interruption in the ring from interfering with the network data communication.
3.1.2

Audio Network

The audio ring network is for the distribution of microphone and DVA audio initiated from the Audio Control
Unit.
The audio is distributed as base-band audio with one twisted wire pair in the network cable being required for
each audio channel.
Three audio channels are normally supported in order to enable concurrent ALERT, EVACUATE and Fire
Microphone audio to be broadcast. Should this level of concurrency not be required, then a fewer number of
network channels can be implemented. An equivalent number of audio channels at each Slave Unit would
then be available for connection of microphones or other audio source. In non-emergency conditions the
audio channels may be used for music and paging functions.
The Network Interface Card in all Slave Units, or the VAR-NIA Network Interface Adapter connected to
VAR12/20 Slave Units, takes the Router inputs as follows:
•
Network Channel 1 – Router Input 1
•
Network Channel 2 – Router Input 3 (if used)
•
Network Channel 3 – Router Input 4(if used)
Tolerance of the audio rings to short circuit is achieved by relay isolation, to isolate any short circuits.
In a fault free condition the audio from the Audio Control Unit is transmitted from the UPSTREAM port. The
audio passes though each Slave Unit, un-buffered. Each Slave Unit merely tapping off the audio.
Because the audio bus is un-buffered at each Slave Unit, a short circuit will cause complete failure of the
ring, and cause all Slave Units to report failures. An open circuit will cause only Slaves downstream of the
fault to report faults.
VAR8 and Variants - Product Description
Issue: 02 complete, approved
Page 27 of 54