LINE PROTECTION SWITCHING SYSTEM

摘要

LINE PROTECTION SWITCHING SYSTEM Protection for service lines linking offices in a communications sytem is realized by linking the offices in a sequence with a serial connection of protection lines. Protection for service lines which bypass one or more of the offices in the serial sequence is achieved by automatically controllably cascading appropriate ones of the protection lines. The cascading of protection lines is realized on a nonhierarchical basis by assigning each service line in the system a unique address and by supplying a protection switch request message including the address of the requesting service line sequentially to each office in the serial sequence until the transmit-end of the requesting line is located. A switch-is automatically effected by equipment located at the offices only if all the protection lines to be cascaded are available. The availability of the protection lines is indicated at each office and an indication thereof is included in the protection switch request message being propagated sequentially to the offices in the system.