Patent ID: 6865158

Claim:
A system comprising: an ATM (asynchronous transfer mode) switch having a plurality of pairs of input and output ports each having different port numbers assigned thereto, wherein an ATM cell arriving at an input port is transferred to an output port depending on internal header information added to the ATM cell; an incoming line circuit connected to each of a plurality of input ports of the ATM switch; and an outgoing line circuit connected to each of a plurality of output ports of the ATM switch wherein the incoming line circuit comprises: a cell discriminator for discriminating a first OAM (operation, administration, and maintenance) cell requiring a response among ATM cells received from a corresponding incoming line; a cell data converter for converting the first OAM cell to a second OAM cell with internal header information indicating an output port of the ATM switch corresponding to the corresponding incoming line so that the second OAM cell is transferred to the output port corresponding to the corresponding incoming line to be sent through a corresponding outgoing line circuit; a header conversion table including an output port number and connection information for each of possible connections identified by header information of incoming ATM cells and further containing endpoint information indicating whether the system is an endpoint of an OAM flow for each level in ATM layer for each of the possible connections; and a header converter for converting an incoming ATM cell by searching the header conversion table for an output port number and connection information according to header information of the incoming ATM cell to add the output port number and connection information to the header information of the incoming ATM cell, wherein the cell discriminator discriminates an AIS (Alarm Indication Signal) cell having a connection relative to endpoint information indicating that the system is an endpoint of an OAM flow for each level in ATM layer and further discriminates a loopback cell when the system is set to a loopback point, and the cell data converter converts the AIS cell to an RDI (Remote Defect Indication) cell and further converts the loopback cell to a return loopback cell.