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OSI Data Link Layer

The second layer in OSI model is the Data Link, a very important layer in ensuring Network connectivity and data delivery. Main functions of Data Link Layer are:

  1. Define Network Protocol (Ex. Ethernet, Token Ring etc)
  2. Ensure Data is delivered to the correct device across Network

Data Link Layer has two sub layers in them

Logical Link Control:

  1. Provides interface for MAC sublayer by utilizing Source Service Access Points and Destination Service Access Points
  2. Manages the Control, Sequence and Acknowledgement of frames
  3. Manages Flow Control

Media Access Control:

  1. Frames the data packets
  2. Manages Error Control
  3. Identifies the MAC access (Media Access Control Address), a unique 48 bit address that identifies the Network device (mostly embedded into the Network Interface Card).
  4. Handles accessing the Media (Token Ring, CSMA/CD used in Ethernet, Polling used in Mainframe, etc)

The MAC address of your windows PC, for example, can be obtained by using ipconfig /all command. See an example output below:

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