The LAN Lower Layers

In the LAN model, the lowest two ISO layers are replaced by three layers:
  1. The Logical Link Control (LLC) Layer
  2. This allows several 'logical' links to exist on the shared medium and indeed several to exist between a pair of attached systems. Three classes of LLC are provided:
    1. Unacknowledged connectionless service.
    2. Connection Oriented service.
    3. Acknowledged connectionless service.
    The service provided by a CO logical links is the same as that provided by the OSI Datalink layer which assures compatibility between the LAN and WAN worlds at the Datalink service interface.
  3. The Medium Access Control (MAC) Layer This defines the procedure to be used for sharing the medium, for example CSMA-CD as used in the Ethernet.
  4. The Physical Layer