Layers of OSI Model

The Open System Interconnection (OSI) model is a conceptual model developed by the International Standards Organization (ISO) in 1984. The OSI model provides a standard for communication between different/diverse computer systems.

The OSI model has seven layers in which each layer has a specific set of functions and communicates with the layer above and below itself.

Layers of OSI mode:

  1. Physical Layer: The physical layer is the lowest layer of the OSI model. It is responsible for transmitting message bits over a medium and it also takes care of mechanical, electrical, procedural, and functional specifications for communication.

    Functions:
    • Transmission mode: It defines a transmission mode from Simplex, half-duplex, and full-duplex.
    • Network Topology: It specifies the arrangement of devices in a network.
    • Physical characteristics of  the transmission medium
    • Line Configuration: It selects from either point-to-point or multipoint line configuration.
    • Data Rate: The physical layer defines the number of bits transmitted per unit of time.
  1. Data Link Layer(DLL): The data link layer breaks data packets received from the network layer into smaller pieces called frames and is responsible for the error-free transmission of these frames from one node to another using its MAC address.

    The DLL is divided into two sublayers:
    • LLC(Logical Link Control): It deals with functions like flow control and error control.
    • MAC(Media Access Control): It controls the physical addressing and framing functions of the data link layer.

Functions:

  • Flow Control: It makes sure that the transmitting speed and the amount of data sent match with the capacity and speed of the receiver so that no data gets corrupted.
  • Framing: DLL adds certain bits at the beginning(called header which contains the source and destination addresses) and at the end(called trailer which contains error correction and detection bits) to the message frame. 
  • Error Control: DLL uses CRC(cyclic redundancy check) to check if any error occurred during transmission.
  • Physical Addressing: DLL adds physical address(MAC address) of destination and source in the header of each frame.
  • Access Control: Determines which device has control over the link if the same communication channel is shared by multiple devices.

Special thanks to Ami Jangid for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article