| 单词 | LAPD (Link Access Procedure, D channel) |
| 释义 | 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 |
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