Sub Layer of Data link Layer

The Data Link Layer, which is the second layer in the OSI model, can be classified into two sublayers:

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  Logical Link Control (LLC):

This sublayer is responsible for providing a reliable data transfer service between end systems over a network. The LLC sublayer provides error control, flow control, and access control services to the network layer. The LLC protocol is independent of the underlying network technology and is responsible for encapsulating packets received from the network layer into frames for transmission over the network.       

The main functions of the LLC sublayer include:

1. 1. Error control: The LLC sublayer provides error control by using error detection and correction techniques to ensure that data is transmitted and received without errors. This helps to ensure the reliability of the data transfer service.
   2. Flow control: The LLC sublayer provides flow control to prevent data loss due to congestion or overloading of the network. The flow control mechanism regulates the flow of data between the network layer and the data link layer.
   3. Access control: The LLC sublayer provides access control to ensure that only authorized devices are allowed to transmit data over the network. The access control mechanism also ensures that the network is used efficiently by regulating the transmission of data.
   4. Multiplexing: The LLC sublayer provides multiplexing by allowing multiple logical connections to share a single physical connection. This helps to optimize the use of network resources.

• Media Access Control (MAC):

This sublayer is responsible for controlling access to the physical medium and managing the transmission of frames between devices on the same network segment. The MAC sublayer is responsible for addressing, framing, and error detection and correction at the physical layer.

The main functions of the MAC sublayer include:

1. 1. Addressing: The MAC sublayer provides a unique hardware address, called a MAC address, to each device on the network. The MAC address is used to identify devices on the network and to route data to the appropriate destination.
   2. Framing: The MAC sublayer is responsible for framing, which involves dividing the data received from the LLC sublayer into smaller units called frames. Each frame contains a header and a trailer, which include information such as the MAC addresses of the source and destination devices and error checking codes.
   3. Error detection and correction: The MAC sublayer provides error detection and correction mechanisms to ensure that data is transmitted and received without errors.
   4. Media access control: The MAC sublayer provides media access control by using a set of rules, known as a media access control protocol, to regulate access to the physical medium. The media access control protocol ensures that only one device can transmit data on the network at a time, to avoid collisions and ensure reliable data transfer.

The LLC and MAC sublayers work together to provide a complete data link layer service. The LLC sublayer provides a common interface to the network layer, while the MAC sublayer provides the means for devices to share the physical medium and transmit frames between each other. Together, the LLC and MAC sublayers provide the necessary functionality for reliable and efficient data transfer over a network.