TDM demultiplexer with dedicated maintenance channels to indicate high-speed line faults to low speed circuits

A TDM demultiplexer for a channel bank at one of several TDM hierarchical levels, comprising:

• a plurality of high-speed interfaces connected respectively to high-speed digital transmission lines, each of said high-speed interfaces receiving TDM digital signals from the transmission line, detecting a line fault in said transmission line and appending an alarm signal having a time-slot duration indicating the line fault to time slots of said digital signals;
• time division multiplexer means for multiplexing output signals from said high-speed interfaces into time slots of a first TDM frame sequence;
• time slot interchanging means for interchanging the time slots of said first TDM frame sequence to produce a second TDM frame sequence according to prescribed relationships between the time slots of said high-speed transmission lines and those of low-speed transmission lines;
• time division demultiplexer means for demultiplexing said second TDM frame sequence into a plurality of TDM signals which are greater in number than the number of said high-speed interfaces;
• and
• a plurality of low-speed interfaces for respectively receiving the demultiplexed TDM signals from said time division demultiplexer means, each of said low-speed interfaces detecting the time slot in which said alarm signal is contained and transmitting a line fault signal to a respective one of said low-speed transmission lines.