At 100G speeds OTN uses a multilane implementation to achieve the OTU4 client interface. Using these multilane interfaces can present a number of challenges and new defect conditions have been defined to support these.
LOFLANE is a loss of frame defect on a logical lane. In some ways it is similar to Loss Of Block Lock (LOBL) on 100G Ethernet however within 100G Ethernet every 64b/66b block includes a sync header so all blocks can be searched for block lock, however in OTN only the OA1&2 bytes have frame alignment functions and so these must be searched for within a lane.
During the receive process for OTU4 the incoming signal from each physical lane of the receiving interface is de-interleaved across the 20 logical lanes. Due to the logical lane rotation process the is utilised in OTN each logical lane will contain the OA1 & OA2 framing bytes every 16320 bytes.
A frame alignment search process is carried out on each of the 20 logical lanes and searches for an OA1 OA2 OA2 pattern.
If the the frame alignment signal cannot be found after 5 of the 16320 byte cycles then an Out Of Frame (OOF) is declared for the specific logical lane.
If the OOF state is maintained on the logical lane for a period of 3ms then a LOFLANE is declared for that lane.