This CucsFabricTrafficDirection field records which direction of traffic — receive, transmit, or both — is being mirrored from the source port for this FC monitoring session's source port. For the physical FC port whose traffic is being mirrored/copied for an FC monitoring session, choosing the wrong direction here is a common reason a monitoring session that looks correctly configured still shows no captured frames on the analyzer, since traffic only flowing the un-mirrored direction is invisible to the capture. An admin troubleshooting a one-way FC performance problem would set this to 'both' rather than 'rx' or 'tx' alone, to be sure they don't miss the direction that's actually misbehaving.