A functional unit that organizes user data into packets according to the X.25 packet layer protocol (PLP) and encapsulates each in an LAPB frame before presenting it to the network.A PAD also may be responsible for password protection and performance reporting. In contemporary X.25 networks, a PAD generally is in the form of software installed on a terminal or a communications server. ITU-T Recommendation X.3 is the specification for a PAD. See also frame, LAPB, packet, PAD, password, PDN, PLP, server, software, terminal, X.3, and X.25.