Abstract: Disclosed is an optical transmission system for transmitting data via an optical transmission line in accordance with a frame format having overhead which includes a K1 byte used for a switching request and a K2 byte used to respond to the K1 byte.

Abstract: A system for processing a plurality of signals in parallel by a plurality of working-system processing units. A protection-system processing unit is provided as a substitute for one of the working-system processing units, and switch units are provided for switching the routes of the signals so that the signals are processed by the protection-system processing unit instead of the substituted working-system processing unit. The characteristic of the protection-system processing unit can be varied automatically under control of a characteristic control unit so that the characteristic of the protection-system processing unit becomes the same as the characteristic of the substituted working-system processing unit.

Abstract: A switching system includes a protection switch that operates to switch a working transmission line to a protection transmission line or switch an optional transmission line to the protection transmission line. The protection switch consists of a first speed converting unit, a second speed converting unit and an add-drop unit that handles a lower order signal and is sandwiched therebetween. The optional transmission line for carrying a lower order signal is connected, via the add-drop unit and the second converting unit, to the protection transmission line carrying a higher order signal during an add-drop operation. Alternatively, the working transmission line carrying a higher order signal is connected, via the add-drop unit and the first and second converting units, to the protection transmission line under a through operation mode. The protection switch is preferably realized by using an add-drop multiplexer (ADM).

Abstract: A pointer processing circuit which is incorporated in a SONET transmission apparatus having a cross connect equipment, is installed in the reception part of the cross connect equipment. The pointer processing circuit detects a phase difference between a multiplexed input frame signal for each input side transmission line, and receives a frame synchronous signal by which output frame signals are commonly synchronized. The frame synchronous signal is produced by a frame counter connected to the pointer processing circuit. The pointer processing circuit has a unit for adjusting a pointer value of the multiplexed input frame signal, based on the thus detected phase difference, before the cross connection of the input frame signals.

Abstract: A system for optical communication between first and second optical terminal stations, containing a plurality of working optical transmission lines each for connecting between the first and second optical terminal stations, a protection optical transmission line. Each of the first and second optical terminal stations contains a plurality of working pieces of optical terminal equipment, connected to the respective working optical transmission lines, a protection piece of optical terminal equipment connected to the protection optical transmission line, and a plurality of bidirectional optical signal paths, provided corresponding to the respective working pieces of optical terminal equipment, and each operative to connect the corresponding working piece of optical terminal equipment to the protection piece of optical terminal equipment.

Abstract: A maintenance signal transmission system incorporates a transmitting station, a receiving station, a main line which connects the transmitting station and the receiving station, and a backup line which connects the transmitting station and the receiving station. The transmitting station at least includes a switch for selectively connecting to one of the main line and the backup line to transmit a main signal and a maintenance signal to the receiving station using the selected line. The receiving station at least includes an adder for adding maintenance signals which are received from both the main line and the backup line. The main and backup lines may or may not take mutually different routes.