OSI Model's Logical Link Control (LLC)
The Role of LLC in the OSI Model
In the seven-layer OSI model, the data-link layer is divided into two sublayers: the Media Access Control (MAC) layer and the Logical Link Control (LLC) layer.
LLC's Functions
LLC provides a uniform interface to the user of the data link service. It handles:
*Framing: Encapsulating data into frames that include control information.
*Error detection: Using checksums to detect errors in frames.
*Flow control: Managing the rate at which data is sent and received.
LLC in the IEEE 802 Reference Model
In the IEEE 802 reference model, LLC is responsible for:
*Data communication: Establishing and maintaining connections for data transfer.
*Logical Link Control (LLC) Protocol Data Unit (PDU): LLC PDUs are encapsulated in MAC PDUs for transmission.
Types of LLC
There are two types of LLC:
*LLC Type 1 (LLC1): Connectionless data transfer, suitable for unreliable networks.
*LLC Type 2 (LLC2): Connection-oriented data transfer, ensuring reliable delivery of data.
LLC in WANs
In Wide Area Networks (WANs), LLC is used in:
*DLSw (Data Link Switching): Carries LAN traffic over a WAN.
*SNA (Systems Network Architecture): Uses LLC2 for data transfer.
LLC2 Acknowledgments
In LLC2 connections, receiving stations must send acknowledgments after receiving a specified number of frames. This ensures reliable data delivery.
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