Data Link Layer

The ISDN (Integrated Services Digital Network) data link layer ensures reliable data transfer across the ISDN network. It operates at Layer 2 of the OSI model and is responsible for framing, flow control, and error management.

Key protocols used at this layer include:

• LAPD (Link Access Protocol for D-channel): This protocol facilitates signaling across the ISDN's D-channel, managing multiple logical connections and ensuring data integrity and orderly delivery.

• HDLC (High-Level Data Link Control): ISDN utilizes HDLC-like framing for B-channels to handle data encapsulation and error detection through checksums.

These protocols collectively ensure efficient and error-free communication between network devices over ISDN links.