In the LAN model, the lowest two ISO layers are replaced by three layers:
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The Logical Link Control (LLC) Layer
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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:
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Unacknowledged connectionless service.
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Connection Oriented service.
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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.
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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.
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The Physical Layer