LAPB
Link Access Procedure, Balanced (LAPB) implements the data link layer as defined in the X.25 protocol suite. LAPB is a bit-oriented protocol derived from HDLC that ensures that frames are error free and in the right sequence. LAPB is specified in ITU-T Recommendation X.25 and ISO/IEC 7776. It can be used as a Data Link Layer protocol implementing the connection-mode data link service in the OSI Reference Model as defined by ITU-T Recommendation X.222.