The HDLC module implements one of the protocols in the Data Link layer.
   The HDLC High-level Data Link Control protocol is intended to cover a
   wide range of applications; for example, one-way, two-way alternate or
   two way simultaneous data communication between data stations which are
   usually buffered, including operations on different types of data
   circuits; for example multipoint/point-to-point, duplex/half-duplex, and
   switched/non-switched. This implementation uses HDLC to offer reliable
   communication at the Data Link layer for point-to-point synchronous data
   lines over a wide area network link.  The HDLC module typically runs as a
   Data Link module under the CLNS Network protocol.

   The hierarchical relationship of the entities that constitute the HDLC
   module:

               HDLC
                 Port
                 Link
                   Logical Station

   You must install the WAN device drivers before you can refer to these
   entities.

   The HDLC entity is the top-level entity in the hierarchy of entities
   belonging to the HDLC module.