Communications (Fibre-Optic)

The Highway 401 COMPASS System in Toronto relies exclusively on fibre-optic cable for its communications between the central computer system and all local field controllers. Fibre optics has an inherent immunity to interference. It also has a much larger bandwidth compared to co-axial, which leaves more room for system expansion.

Data communication is typically full duplex, operating asynchronously at 9600 bits per second. Communication between controllers and the FTMS Computer uses a poll/response protocol over multiple access communication circuits. The camera control transmitter and the FTMS Computer provide the access protocol to the communication circuits.

The data communication system is a two-tier system with a high speed backbone Data Ring Network supporting low speed (9600 bits per second) distribution from drop and insert nodes.

The high speed system consists of nodes interconnected by optical fibres. The optical fibres originate at the TOC and loop across the highway at the geographical ends of the FTMS, thereby creating Data Ring Networks. The communications subsystem is a high speed data ring interfacing to fibres installed in previous contracts. The nodes operate in a dual ring configuration so that each data ring network can maintain full connectivity between nodes and the TOC in the event of a cable, fibre or node failure.

The nodes drop and insert data from preselected time slots in a high speed time division multiplexed data aggregate channel and provide physical access to these time-slots from data channel ports connected to the node. Distribution from the data channel ports to field controllers is either local or through a combination of port sharing devices, fibre optic modems, fibre optic splitter and fibre optic taps. Port sharing devices allow multi-drop low speed circuits to share a data channel port. Fibre optic modems allow the creation of a multi-drop fibre optic low speed circuit or point to point fibre optic low speed communication.

The advent of the Advanced Traffic Controllers (ATC) to replace the current Type 170F controllers will remove the requirements to communicate at low speed (9600 bits per second). A study is under way to look at a new high speed communications system.

See also:

• Traffic Operations Centre (TOC)
• Central Computer System
• Closed Circuit Television (CCTV)
• Vehicle Detector Stations (VDS)
• Changeable Message Signs (CMS)
• Ramp Metering Stations (RMS)
• Field Provisions (ducts, cabinets, footings, power, etc.)
• Communications Subsystems:
  • Fibre-Optic
  • Coaxial