Trunk line format for telephone communication - has control signalling system for free channel detection in pulse code modulated system

摘要

The line format is a 24 channel multiplexed system which carries pulse code modulated voice signals at 32 or 64 kilobits per second. The multiplex system is the conventional CCITT T1 type which is suitable for short distance, heavy traffic use in metropolitan areas. The format allows a maximum of 15 consecutive '0' bits in any bit-stream. 32 kilobit per second signalling channels are used to identify free lines in the frame i.e those in which more than 15 consecutive '0' bits are transmitted. The operation of the transmission channels is controlled, at the exchanges at each end, by firmware implemented by digital signal processors and the necessary coding logic.