Lenkelaget

Lenkelaget, or the data link layer, is the second layer of the OSI model. It provides node-to-node data transfer over a single physical link by encapsulating network-layer packets into frames, performing addressing, and ensuring frame integrity through error detection. The layer also handles flow control to manage data rate between adjacent devices.

The data link layer is commonly divided into two sublayers: the MAC (media access control) sublayer and the LLC (logical link control) sublayer. The MAC sublayer manages access to the shared physical medium and uses hardware addresses (MAC addresses) to identify devices on the same network segment. The LLC sublayer presents a link-layer interface to the network layer, and can offer multiplexing and basic error-management features, helping to separate network-layer protocols from link-layer specifics.

Technologies that implement lenkelaget include Ethernet, Wi-Fi (IEEE 802.11), PPP, and HDLC. In Ethernet, frames contain destination and source MAC addresses and a frame check sequence for error detection. Switches and bridges primarily operate at this layer, forwarding frames based on MAC addresses and, in many networks, supporting VLAN tagging (802.1Q) to partition broadcast domains.

Limitations: the data link layer provides reliable delivery only over a single link or local segment; end-to-end reliability is not guaranteed and is typically handled by higher layers such as the transport layer. The layer interacts with the physical layer below it to transmit bits and with the network layer above it to deliver data to the appropriate upper-layer protocols.