Computer Networks Lecture 10: Data Link Layer

Data Link Layer Responsibilities

• The main responsibility of the Data Link layer is to transfer data from one node to an adjacent node.

Data Transfer Process

• The Data Link layer transfers data by encapsulating packets from the Network layer into frames.
• Frames are then transmitted over a single link to the adjacent node.

Hardware Implementation

• The Data Link layer can be implemented using network interface cards (NICs) and Ethernet switches.

Framing Function

• The Data Link layer is responsible for framing, which involves breaking data into frames and adding headers and trailers.

Sublayers

• The Logical Link Control (LLC) sublayer is responsible for managing and controlling the flow of data between devices.
• The Media Access Control (MAC) sublayer is responsible for controlling access to the shared network medium.

Error Detection

• A multi-bit error involves two or more bits in the data unit changing from 0 to 1 or vice-versa, regardless of whether they occur in consecutive bits.
• Two-dimensional parity checking calculates parity check bits for each row and column to detect errors.
• Cyclic Redundancy Check (CRC) is used for error detection to ensure that the received data is accurate and error-free.
• Simple parity checking, or one-dimension parity check, adds a single bit to the data to detect errors.

Error Control and Flow Control

• Error control in the Data Link layer aims to address errors in data transmission.
• Flow control ensures that the sender does not send more data than the receiver can handle, preventing data loss.