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What are the functions of logical link control in data link layer?

Published in Data Link Control 2 mins read

The Logical Link Control (LLC) sublayer within the data link layer is primarily responsible for managing the logic of data transmission. Specifically, it handles synchronization, flow control, and error checking.

Functions of Logical Link Control (LLC)

The LLC sublayer is a crucial part of the data link layer, which bridges the gap between the network layer above and the media access control (MAC) sublayer below. Its main functions can be broken down as follows:

  • Synchronization:

    • Ensures that both sender and receiver are properly aligned and agree on the timing of data transmission.
    • This process helps prevent data loss or corruption due to mismatched transmission rates.
    • For example, LLC manages start and end bits of a frame to signal start and end of transmission.
  • Flow Control:

    • Manages the rate at which data is transmitted to prevent overwhelming the receiver.
    • It adjusts the transmission speed based on the receiver's ability to process incoming data.
    • This avoids packet loss due to buffer overflow at the receiving end.
    • Examples of flow control mechanisms include using acknowledgments, such as send and receive window sizes.
  • Error Checking:

    • Detects errors that may have occurred during data transmission.
    • It uses mechanisms to ensure that data is received correctly without alterations.
    • Error detection mechanisms are included in the LLC header. These mechanisms could be using checksum or cyclic redundancy check (CRC) methods.
    • If errors are detected, the LLC may initiate procedures like retransmission of lost or corrupted data.

LLC in Practice

In essence, the LLC ensures a reliable and orderly flow of data between two nodes on a network, making sure that no data is lost or corrupted during the exchange. It sits on top of the MAC layer, which handles the physical aspects of transmission like medium access and physical addressing. Think of the LLC as the traffic controller of the data link layer.

Function Description
Synchronization Aligns sender and receiver timing; manages frame start/end.
Flow Control Adjusts data transmission rates to avoid overwhelming the receiver.
Error Checking Detects errors during transmission; initiates retransmission if needed.