What is Logical Link Control (LLC) All About?
Logical Link Control (LLC) is a sublayer of the Data Link Layer in the Open Systems Interconnection (OSI) model. It provides a service interface between the Media Access Control (MAC) sublayer and the Network Layer.
LLC Functions:
The LLC sublayer is responsible for several functions, including:
- Multiplexing and demultiplexing – Multiplexing is the process of combining multiple data streams into a single transmission channel. On the other hand, demultiplexing involves separating a single transmission channel into multiple data streams at the receiving end
- Flow control – Process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. It should be distinguished from congestion control, which is used for controlling the flow of data when congestion has actually occurred
- Error detection and correction – Process of detecting errors caused by noise or other impairments during transmission from the transmitter to the receiver. Error correction, on the other hand, involves detecting errors and reconstructing the original, error-free data
- Link establishment and termination – Link establishment refers to the process of setting up a connection between two nodes in a network. This often involves a multi-step handshake process that establishes a connection before entering the data transfer phase. After the data transfer is completed, link termination closes the connection and releases all allocated resources
The LLC sublayer does not define any specific protocols but rather provides a framework for protocols to operate within. This allows different protocols to coexist on the same network medium and to be transported over the same network.
LLC Types Of Services
The Logical Link Control sublayer offers two types of services:
- Connectionless service: This service provides best-effort delivery of data. There is no guarantee that data will be delivered in the correct order or that it will not be lost.
- Connection-oriented service: This service provides guaranteed delivery of data. Data is delivered in the correct order and is not lost.
The LLC sublayer is used by a variety of networking protocols, including IP, IPX, DECnet, and NetBIOS.
Conclusion
In summary, the LLC sublayer is an important part of the OSI model and plays a vital role in the reliable delivery of data over a network. It provides a framework for different protocols to operate within and offers both connectionless and connection-oriented services to ensure the efficient delivery of data.
