The Data Link Layer (DLL) is the second layer of the seven-layer OSI model of computer networking. It is responsible for providing reliable data transfer between two nodes on a network. The data link layer does this by using error detection and correction techniques to ensure that data is not lost or corrupted during transmission.

The data link layer is divided into two sublayers: the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer. The MAC sublayer controls how devices on a network can access shared resources, such as a Wireless (LAN) Local Area Network (WLAN) or Ethernet cable. The LLC sublayer handles error correction, flow control, and frame synchronization.

Frame relay and Asynchronous Transfer Mode (ATM) are two popular protocols that operate at the data link layer. Frame relay uses virtual circuits to send data between nodes, while the ATM uses fixed-size cells to transport information across networks.