An ATM switch system provided at each node in an ATM network, which switches over a working channel to a protection channel, within a protection domain of a duplicated channel segment constituting the working and protection channels, the ATM switch system comprising:
- an ATM switch circuit performing a cell switching function;
- external line interface portions each inserting cells, located at an external line side;
- internal line interface portions each extracting cells, located at an internal line side;
- a multiplexer multiplexing cells input from the internal line interface portions and interfacing with the ATM switch circuit;
- a demultiplexer interfacing with the ATM switch circuit and demultiplexing multiplexed ATM cells;
- and
- a controller,
- wherein demultiplexer of an ATM switch system of a source node located at a starting point of the protection domain identifies a connection for APS processing, and duplicates cells on a working channel to a protection channel,
- an ATM switch system at an intermediate node located downstream from the starting point of the protection domain detects a failure on the working channel and transmits an AIS cell in a down stream direction toward an ATM switch system of a destination node located ax a terminal point of the protection domain,
- the ATM switch system of the destination node located at the terminal point of the protection domain detects the AIS cell, and transfers it to the controller,
- the controller orders the ATM switch system to switch over from an internal line interface portion at which the working channel is terminated to another internal line interface portion at which the protection eel is terminated, and
- the multiplexer allows only ATM cells identified as the connection for APS processing, and
- wherein the in the interface in the ATM switch at the intermediate node includes a VPI/VCI converting table a header modification portion and an alarm cell insertion circuit,
- refers to the VPI/VCI converting, table using as a reference key an internal channel and a channel identifier for an input ATM cell to obtain a external channel to be output in the external line interface portions and a virtual channel identifier,
- sets the obtained virtual channel identifier on the ATM cell at the header modification portion, and
- when detecting a failure between the upward staring point and the intermediate node, inserts an alarm cell at the alarm cell insertion circuit according to a control command from the controller.