Line protection switch controller

A line protection switch used to bridge as impaired one of a plurality of regular digital channels with a digital protection channel so both channels are carrying the same digital signal;

• switching means for substituting the digital signal of the protection channel for the impaired regular channel;
• monitoring means for indicating when each digital channel is impaired and when a digital channel is in extreme error condition by signaling an out-of-frame condition;
• delaying means for adjusting the relative relay of the signals from the protection channel and the impaired channel;
• said delaying means capable of adjustment in fine steps fractionally related to a bit period and in steps equal to a bit period;
• means for deriving a clocking signal from the digital signal of each digital channel;
• detecting means for indicating alignment of the adjusted relative delay of the two channel signals to produce a data alignment output and receiving clocking signals, one derived from each channel, to produce a clock alignment output;
• controlling means including a microprocessor programmed to follow a process, said controlling means bypassing the process when an out-of-frame condition is indicated by forcing said switching means to switch directly without obtaining channel alignment, said controlling means producing clock alignment by varying the adjusted relative delay in fine steps in a first direction and reversing the direction of the adjusted relative delay in small increments until the detecting means indicates clock alignment, said controlling means provided data alignment by producing relative bit steps in the data signal in a first direction and then in an opposite direction until the detecting means indicates data alignment;
• and
• switching means for substituting the signal of the protection channel for the regular channel after both clock alignment and data alignment are achieved.

In a transmission system having a plurality of regular channels and a spare channel substituted for one of the regular channels so that both channels are carrying the same digital signal with the spare channel being in service, apparatus for restoring the service back to the one regular channel comprising:

• shifting means for adjusting the relative timing of the digital signals between both channels in increments fractionally related to the duration of a bit in the digital signals and in steps equal to a bit period;
• detecting means, coupled to receive the digital signal of the one regular channel and the spare channel, for indicating alignment of the digital signals of both channels, said detecting means including clocking means associated with each channel for deriving a clocking signal from their digital signals, said detecting means coupled to receive the clocking signals and indicating bit alignment;
• and
• controlling means for serving to produce an alignment indication by said detecting means, said controlling means checking for bit alignment indication from the detecting means before adjusting the shifting means in a first direction in increments to a first extreme value, said controlling means checking for bit alignment indication before adjusting the shifting means in increments in an opposite direction, said controlling means checking for signal alignment while adjusting the shifting means in steps in a first direction to predetermined extreme value and then in the opposite direction until signal alignment is indicated, and said controlling means directing the restoration of the regular channel for service to free the spare channel when signal alignment is first indicated by said detecting means.