Expanding switching capability of a time division communication system

Abstract

A TDM (Time Division Multiplexed) telephony switching system which provides expanded switching capacity without change in the physical form factor of the system or of the design of the circuits which provide TDM multiplexed digital signals (the port and service circuits). Additional ports and service circuits are provided in the same number of time slots per frame as existed before system expansion thereby providing additional ports and/or service circuits which can be interconnected without significantly affecting the cost of the system. Expansion is achieved by multiplexing the digital signals and transmitting them at a higher rate on existing send highways of the system. The time slot interchange is expanded by providing a memory with additional locations for each group of additional circuits. The signals are demultiplexed and switched in the time slot interchange and transmitted on receive highways (additional receive highways being provided for the additional groups of circuits) at the rate at which the existing port and service circuits are designed to operate. The expanded system is, therefore, compatible since the highway signals as seen from the circuits being switched are unchanged. Also, the existing design of the shelves, and the back plane interconnecting board thereof, is compatible with the expanded system.