(1) (Link Access Procedure) An ITU family of data link protocols that are subsets of HDLC, which was derived from IBM's SDLC protocol. See HDLC.

LAP-B (Link Access Procedure - Balanced)
LAP-B is used in X.25 networks. Multilink Procedure (MLP) is a LAP-B extension that supports multiple, simultaneous links for increased throughput.

LAP-D (Link Access Procedure for the D Channel)
LAP-D is used for the D channel in ISDN networks and is defined in the ITU Q.920 and Q.921 recommendations. See ISDN.

LAP-M (Link Access Procedure for Modems)
LAP-M is used in V.42 error correcting modems. Although transmission between the computer and modem is asynchronous, transmission between LAP-M modems is synchronous.

LAP-X (Link Access Procedure Half-Duplex)
Used in ship-to-shore transmission.

(2) (Link Access Protocol) The data link protocol in an AppleTalk network. Support for the various data link types are known as ELAP (Ethernet LAP), TLAP (Token Ring LAP), FLAP (FDDI LAP) and LLAP (LocalTalk LAP).