Link Access Procedures, D channel

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In Integrated Services Digital Network (ISDN) telecommunications, Link Access Protocol, D channel is part of the network's communications protocol which ensures that messages are error free and executed in the right sequence.

LAPD is the second layer protocol on the ISDN protocol stack in the D channel (the ISDN channel in which the control and signalling information is carried).

LAPD standards are specified in ITU-T Q.920 and Q.921. Its development was heavily based on High-Level Data Link Control.

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