A Carrier Sense Multiple Access with Collision Detection CSMA/CD Local Area
   Network LAN provides high-speed communications channels for connecting
   computers and other digital devices located within a moderate-sized
   geographic area.  Like other LANs, the CSMA/CD LAN falls between
   long-distance, low-speed networks that carry data for hundreds or thousands
   of kilometers, and specialized, high-speed intercommunications that are
   generally limited to tens of meters.  The CSMA/CD LAN is intended primarily
   for use in such areas as office automation, distributed data processing,
   terminal access, distributed systems, and other situations that require
   economical connection to a local communication medium with sporadic traffic
   at high-peak data rates.

   The entities that constitute the CSMA-CD module are listed below. The
   indentation indicates the hierarchical relationships between the entities.

                                CSMA-CD
                                   Port
                                   Station

   The CSMA/CD module incorporates the functions and operations defined in
   the Ethernet Specification V2.0 and the ISO 8802-3 IEEE 802.3 CSMA/CD
   Access Method and Physical Layer specification as well as parts of the ISO
   8802-1 IEEE 802.1 Addressing, Internetworking, and Network Management and
   the ISO 8802-2 IEEE 802.2 Logical Link Control specifications.  To this,
   the CSMA-CD module adds features often needed by users of the Data Link.
   A typical such Data Link user is the Network Layer.

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