This field records the local physical port number that this SAN uplink port maps to on its fabric interconnect or fabric extender. For one physical FC or FCoE uplink port that is a member of the fabric interconnect's SAN cloud, this port number is the piece of information an on-site technician actually needs to find the right physical port on the chassis, since the DN alone is not something you can read off a faceplate. For instance this instance might report port 20, meaning it corresponds to the physical port labeled 20 on that switch's faceplate.