LAPD (Link Access Procedure, D channel)

Pronounced lap dee. A bit-oriented protocol that is part

of the ISDN protocol suite, LAPD runs at Layer 2, the Data Link Layer, of the OSI Reference Model.

LAPD defines the ISDN data (D) channels, which are designated for out-of-band signaling and control purposes in all ISDN implementations. LAPD evolved from the LAPB protocol used in X.25 networks.

As the Signaling System 7 (SS7) signaling and control network specified for ISDN employs the X.25

packet format, consistency is maintained in the packet format, end-to-end. LAPD is a balanced protocol that operates in asynchronous balanced mode (ABM), referring to the fact that the devices have a balanced (i.e., peer-to-peer) relationship, rather than a master/slave relationship. Figure L-2 illustrates the LAPD

frame and its component fields.

Field Length

in octets

1

2

1 or 2

< 260

2

1

Flag

Address Control

Frame Check

Information

Flag

Sequence

Frame Header

Frame Trailer

• 1/3 FEC
• 14
• 15
• 1.5-way paging
• 16
• 16-QAM
• 16-QPSK
• 18
• 1:8 Splitter
• 1A
• 1A1
• 1A2
• 1Base5 (1 Mbps; Baseband; 500 meters)
• 1B+D
• 1. Domain Name System. The naming convention that divides the Internet into logical domains identified in Internet Protocol version 4 (IPv4) as a 32-bit portion of the total address.The standard convention is user@organization.domain, where user is the name of the end user, organization is the name of the enterprise or other organization owning or sponsoring the address, and domain is the type of entity owning or sponsoring the address.The administration of the DNS is the responsibility of Internet Corporation for Assigned Names and Numbers (ICANN). See also domain, ICANN, Internet, and IPv4. 2.
• 1. In storage, irrelevant material, usually zero (0) bits, added to a data block in order to fill it to a minimum size, to force certain fields of control data or user data into certain positions or sizes, or to prevent the user data from duplicating a bit pattern that has a specific control meaning. See also block. 2.
• 1 cps, 1 Hz
• 1+ Dialing
• 1G (1st Generation)
• 1G (1st Generation)
• 1-persistent carrier sense multiple access (1-Persistent CSMA)
• 1-Persistent CSMA (1-Persistent Carrier Sense Multiple Access)
• 1+ WATS
• 1xEV-DO (one carrier EVolution-Data Optimized)
• 1xRTT (one times Radio Transmission Technology)