Layer 3 of the seven-layer Open Systems Interconnection (OSI) Reference Model. Software at the Network Layer is responsible for addressing and sequencing the message units and transporting them to their ultimate destinations, setting up the appropriate paths between the nodes. At this layer, message routing, error detection, and control of internodal traffic are managed. The Internetwork Protocol (IP) operates at this layer. See also IP, layer, network architecture, OSI Reference Model, protocol, routing, and software.