Nortel Networks 8672ATMM - Manual (Page 26)

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1. Remote defect indications (RDI) indicates that a failure has occurred at
the far end of the network. In ATM, when the physical layer detects loss
of signal or cell synchronization, RDI cells are used to report a VPC/
VCC failure. RDI cells are sent upstream by a VPC/VCC endpoint to
notify the source VPC/VCC endpoint of the downstream failure.