What is Logical Link Control(LLC)?
Logical Link Control (LLC) offers essential data link protocol functions such as error control and flow control. It shares similarities with well-known data link protocols like Synchronous Data Link Control (SDLC) or High-Level Data Link Control (HDLC). However, the distinguishing feature of LLC is its inclusion of service access points (SAP) information within frames, enabling multiple applications on one station to simultaneously communicate with applications on other stations in the network.
LLC provides three primary services for local network applications
- Unacknowledged Connectionless Service: This service operates like a datagram, requiring no connection establishment overhead. It doesn’t provide acknowledgments to guarantee frame delivery.
- Acknowledged Connectionless Service: In contrast, this service ensures acknowledgment for received frames, reducing the burden on higher layers by confirming successful frame delivery.
- Connection-Oriented Service: This service offers more advanced features, including flow control, sequencing, and error recovery between SAPs. It also facilitates the multiplexing of logical endpoints over a single physical link.
Functions of LLC (Logical Link Control) Sublayer
- Multiplexing and Demultiplexing
- Function: The primary role of LLC is to multiplex protocols over the MAC layer during transmission and demultiplex them while receiving.
- Explanation: LLC ensures efficient sharing of the communication medium by combining multiple protocols over the same MAC layer.
- Hop-to-Hop Flow and Error Control
- Function: LLC provides hop-to-hop flow control and error control.
- Explanation: It manages the flow of data between two directly connected devices, controlling the rate of data transmission and handling errors that may occur during the communication.
- Multipoint Communication
- Function: LLC facilitates multipoint communication over a computer network.
- Explanation: It supports communication between multiple devices in a network, allowing data exchange between different nodes.
- Frame Sequence Number
- Function: LLC assigns frame sequence numbers.
- Explanation: It assigns unique identifiers to frames for tracking and organizing data transmission. This aids in managing the order and integrity of transmitted frames.
- Acknowledgment Tracking
- Function: LLC tracks acknowledgments, particularly in acknowledged services.
- Explanation: In situations where acknowledgment of received data is required, LLC monitors and tracks acknowledgments to ensure the reliable delivery of data between communicating entities.
The Logical Link Control (LLC) sublayer plays a major role in multiplexing and demultiplexing protocols, ensuring reliable communication with hop-to-hop flow and error control, supporting multipoint communication, managing frame sequence numbers, and tracking acknowledgments for enhanced data reliability.