csOc3LineCurrentStatus is a read-only bitmap value, encoded as a sum such as csOc3LineNoDefect, csOc3LineAIS, and csOc3LineRDI, reporting the current defect status of the SONET/SDH Line layer on this OC3 port, capable of representing multiple simultaneous defects. A Line-layer AIS typically means an upstream failure is being relayed downstream, while RDI means the far end is reporting a problem back to this port, so decoding this bitmap tells an admin which direction of the link has the actual fault. For example, if csOc3LineCurrentStatus shows the RDI bit set while the local Section layer looks clean, an admin knows the problem is on the far end's receive path rather than on this port's own transmitter.