LAPD - Link Access Protocol on the D Channel

Link Access Protocol on the D channel is a Layer 2 protocol used on the ISDN D channel. LAPD was derived from the LAPB (Link Access Protocol Balanced) protocol and was designed to satisfy the signalling requirements of ISDN basic access. LAPD is defined in the ITU-T (International Telecommunications Union-Telecommunication Standardization Sector) recommendations Q.920 and Q.921.


  • Fully interactive 3GPP based network map
  • Narrated call flows
  • Detailed network procedures

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