PDF user manual for CopperEdge 150

Node ANode B Node C Node DRDIRDIAISRDIATM ConnectionEnd PointA Fault on the Upstream ConnectionATM ConnectionEnd PointIn the diagram above, the device at Node C senses the fault onthe upstream between Node B and Node C. It sends an AIS messageto the device on the endpoint at Node D. The device at NodeD responds and sends a RDI message to the device on the otherend of the WAN connection. The message goes through becauseno fault is present on the downstream part of the connection.At this time, devices at both ends of the connection know theupstream path on the connection has a fault is broken, andtwo-traffic has stopped. Loopback testing can begin from thedevices at either end to determine the exact location of the fault.7UDQVPLWWLQJDQG5HFHLYLQJ/RRSEDFN0HVVDJHVTo determine the exact location of the fault, system administratorsmust use the OAM fault management function on one orboth of the devices at the endpoints of the connection. Administratorscan set a device to automatically send Requests forLoopback cells to a device at the other end of the connection ona regular basis; or they can set a device to send Requests forLoopback cells on a manual basis. Then administrators canread the counters for Requests for Loopback cells and thecounters for Responses to Loopback Requests.But to locate the fault, if the connection has multiple segments,someone must look at the counters for Requests and Responseson devices located on intervening segments. The fault on theconnection will be between the last device to receive Requestsfor Loopback cells and the first device to not receive those sameRequests for Loopback cells.Node ANode B Node C Node DLoopbackRequestNo LoopbackResponse*End PointNo LoopbackResponse** After a specified interval, a Loopback Failure occurs.Lookback Request/No ResponseLoopbackRequestEnd Point&KDSWHU$GYDQFHG&RQILJXUDWLRQ