What is the switching architecture of the system 85 PBX?

The switching architecture of the System 85 PBX is a time-space-time architecture. Each peripheral module, called Communication Switching Module (CSM), contains a time stage. The space stage is called the Time Multiplexed Switch (TMS). Up to 31 CSMs can be connected to the TMS via 32 Mb/s fiber optic links and to the Control Complex via 4 Mb/s data channels.