The Data Link Layer of the OSI (Open Systems Interconnection) model is divided into two sub-layers:
Logical Link Control (LLC) Sub-Layer: The LLC sub-layer is responsible for managing link control functions that are not dependent on the specific physical medium. It deals with issues such as flow control, error checking, and framing. LLC is primarily concerned with providing a reliable link between two directly connected nodes.
Media Access Control (MAC) Sub-Layer: The MAC sub-layer is responsible for controlling access to the physical network medium. It deals with issues such as addressing, framing, and media access control. The MAC sub-layer ensures that frames are correctly transmitted over the network medium and that different devices on the same network can uniquely identify each other.
Functions of the Data Link Layer:
Framing: The Data Link Layer encapsulates network layer packets into frames. Frames include delimiters to mark the start and end of the frame, as well as addressing information.
Addressing: The MAC sub-layer adds a hardware address (MAC address) to the frame to uniquely identify the source and destination devices on a network.
Media Access Control: The MAC sub-layer is responsible for controlling access to the network medium to avoid collisions in shared media environments. Different media access control methods, such as CSMA/CD (Carrier Sense Multiple Access with Collision Detection) for Ethernet, are implemented at this layer.
Error Detection and Correction: The Data Link Layer includes mechanisms for detecting and, in some cases, correcting errors that may occur during the transmission of frames.
Flow Control: The LLC sub-layer may implement flow control mechanisms to manage the flow of data between devices, ensuring that one device does not overwhelm another with too much data.
Logical Link Control: The LLC sub-layer manages communication between devices on the same network. It provides services such as connection establishment, maintenance, and termination, as well as error recovery and flow control.
Duplexing: The Data Link Layer can support either half-duplex or full-duplex communication, depending on the networking technology.
The Data Link Layer acts as an interface between the Network Layer (Layer 3) and the Physical Layer (Layer 1) of the OSI model. Its primary goal is to provide reliable and efficient communication between directly connected nodes on a network. The specific functions and features may vary based on the networking technology used (e.g., Ethernet, Wi-Fi, etc.).
