This is the logical port number of this specific interface on its physical port, uniquely identified across the network as NodeId.lportSlotId.lportPportId.lportId, and defaults to 1 for a simple one-to-one physical-to-logical mapping except for special cases like fractional T1 bundles (ufr/nfr/trk) or pdntrk ports where it encodes a bundle number. Understanding what this number actually represents on this specific logical port requires knowing its lportProtocol, since the same numeric value means the only channel on this port for a simple V.35 circuit but this specific bundle number for a fractional T1 configuration sharing the same physical port. A logical port with lportId of 1 on a plain V.35 physical port is simply that port's only channel, whereas an lportId of 3 on a fractional T1 bundle configuration identifies the third of several bundles carved out of that same physical T1.