No.1 ESS Switching Network Framers and Circuits

The switching network is a major functional unit in a telephone central office, representing in many cases 50 per cent or more of the equipment in the office. The choice of apparatus and general circuit design is highly influenced by the search for the optimum balance between cost, reliability, and maintainability. The switching network serves the function of interconnecting the many lines and trunks served by the telephone office. In addition, the network interconnects the lines and trunks with the many service circuits and tone sources, such as signal transmitters, signal receivers, party test circuits, coin supervisory circuit, ringing circuit, etc. A second function of the network is to match the traffic between a large number of lightly used lines and a much smaller number of heavily used trunks, maintaining a satisfactorily low probability of blocking. These basic functions arc performed in an operating environment that slowly changes over the life of the office. Not only can the number 2221