Layer 2 of the seven-layer Open Systems Interconnection (OSI) Reference Model. Software at the Data Link Layer is responsible for addressing, signal formatting (i.e., line encoding and decoding), framing, frame synchronization and sequencing, flow control, error control, and otherwise managing traffic between devices across a link. HDLC, LAP-B, and LAP-D are Data Link Layer protocols, as is frame relay. Local area networks (LANs) operate at the Data Link and Physical Layers. See also error control, flow control, frame relay, HDLC, LAP-B, LAP-D, layer, link, network architecture, OSI Reference Model, protocol, software, and synchronization.