Tiedonvälityskerroksen

Tiedonvälityskerroksen, known in English as the Data Link Layer, is the second layer of the OSI (Open Systems Interconnection) model, situated between the Physical Layer below and the Network Layer above. Its primary function is to provide reliable and efficient data transfer across a physical link. This layer is responsible for error detection and correction, ensuring that data is transmitted without corruption. It achieves this by using techniques such as parity checks, checksums, and cyclic redundancy checks (CRCs).

Another crucial role of the Data Link Layer is media access control (MAC). In shared network environments, multiple devices might attempt to transmit data simultaneously, leading to collisions. The MAC sublayer manages how devices access the transmission medium and arbitrates these potential conflicts, preventing data loss. This is commonly seen in technologies like Ethernet, where MAC addresses are used to uniquely identify devices on a local network.

Furthermore, the Data Link Layer frames data received from the Network Layer into manageable units called frames. These frames contain not only the data payload but also header and trailer information, which includes source and destination MAC addresses, error-checking codes, and control bits for managing the flow of data. The layer handles the transmission and reception of these frames, ensuring that they are delivered to the correct destination on the local network segment. Protocols like PPP (Point-to-Point Protocol) and HDLC (High-Level Data Link Control) operate at this layer.