100A Protection Switching System

The high reliability demanded of microwave radio relay systems requires t h a t protection be provided against system outages t h a t occur as a result of fading or equipment failures. This protection is obtained by frequency diversity through the use of standby protection channels and an automatic protection switching system. E a c h radio relay route is divided into a number of switching sections, each of which m a y contain up to ten radio repeaters. One or two of the total number of radio channels in the switching section are designated as protection channels. The automatic protection switching system uses the protection channels to replace failed regular channels by operat2295 2310 T H E BELL SYSTEM TECHNICAL JOURNAL, DECEMBER 10(15 ing IF switches at the transmitting and receiving ends of the switching section. By manual operation of the IF switches, the protection channels m a y also serve as alternate facilities during an emergency or while maintenance is being performed on a regular channel. T h e original protection switching system developed for use with the long haul T D - 2 system has a capability of protecting any one of the five regular working channels with one protection channel. 1 It was first placed in service in 1953 and since t h a t time has given consistently good performance. About 1960 the T D - 2 system was expanded to 12 channels through the use of channels placed interstitially with the original 6, and m a n y routes are now equipped with both the regular and the interstitial channels.