Clock recovery system capable of automatically switching a direction of a clock pulse sequence from one to another

A clock pulse recovery system for use in a ring-shaped synchronization network in which a master transmission device and a plurality of slave transmission devices are connected in a ring shape to one another and are communicable with one another in clockwise and counterclockwise directions through a selected one of clockwise and counterclockwise transmission paths, and in which a master clock pulse sequence is transmitted in a normal state from said master transmission device in a selected one of the clockwise and the counterclockwise directions, wherein each of said slave transmission devices operates in accordance with said master clock pulse sequence in said normal state, at least one of said slave transmission devices comprising:

• detecting means for detecting interruption of said master clock pulse sequence sent from said master transmission device in said selected one of the clockwise and the counterclockwise directions, to detect an extraordinary state different from said normal state;
• switching means for switching operation from said master clock pulse sequence to an internal clock pulse sequence on detecting said interruption of said master clock pulse sequence;
• and
• informing means for informing said master transmission device of the interruption of said master clock pulse sequence via interruption information sent in accordance with said internal clock pulse sequence in the selected one of the clockwise and the counterclockwise directions;
• said master transmission device comprising:
• receiving means for receiving said internal clock pulse sequence together with said interruption information;
• and
• transferring means for transferring said master clock pulse sequence after reception of said interruption information to said at least one of said slave transmission devices which detected said interruption, and any intervening slave transmission devices, in a remaining one of the clockwise and the counterclockwise directions that is reverse to said selected one of the clockwise and the counterclockwise directions, to deliver said master clock pulse sequence to said slave transmission devices in the remaining one of the clockwise and the counterclockwise directions through a remaining one of the clockwise and the counterclockwise transmission paths opposite to the selected one of the clockwise and the counterclockwise transmission paths by successively switching the selected one of the clockwise and the counterclockwise transmission paths of said slave transmission devices to the remaining one of the clockwise and the counterclockwise transmission paths beginning with a nearest one of said slave transmission devices nearest to said master transmission device, to said at least one of said slave transmission devices.