The SDLC entity provides support for communication links.
   There is only one instance per node. For each physical line, SDLC
   creates a Link subentity, which manages all stations on the line.
   For each logical station, SDLC creates a Station subentity that is
   subordinate to the Link entity, which manages the station. For each
   enabled Station that establishes a connection, SDLC creates a Port
   entity.