The IWU (Inter Working Unit) performs the interface towards the PBX. Up to 8 IWU cards can be plugged into the WMS. The number of IWU cards actually installed depends on the number of cordless handsets to be subscribed to the system, i.e. one analogue line corresponds to one handset. Each card performs 8 analogue line interfaces to the PBX, i.e. a possibility of subscribing up to 8 handsets.
Consequently the maximum number of handsets subscribed to one Control Unit will be 64, but in case of linking two WMS together the maximum capacity of the system will be increased to128 handsets.

The analogue PBX interface contains the following possible settings:

• Signalling: DTMF or Pulse
• Recall function: Loop break / Earth Pulse
• Ringing frequency: 25 Hz - 50 Hz
• Public network: Dial tone detect pause
• Transmission: Parallel operation down to 8 mA