Abstract

In a control system for switching between a first system and a second system of a duplicated selecting structure in an ATM exchange, one of the first and second systems operates as an active system, and the other operates as a standby system. A generator unit writes specific bits into ATM cells received via an input transmission line. The specific bits respectively written into ATM cells to be transferred via the active system indicate a first state, and those respectively written into the ATM cells to be transferred via the standby system indicate a second state. A first table stores the specific bits respectively assigned to VPI/VCI pairs related to the ATM cells transferred via the first system. A second table stores the specific bits respectively assigned to VPI/VCI pairs related to the ATM cells transferred via the second system. A selecting unit compares the specific bits written into the ATM cells with the specific bits stored in the first and second tables by using the VPI/VCI pairs of the ATM cells, and outputs only ATM cells respectively having specific bits respectively indicating the first state to an output transmission line.