LAPB (Link Access Procedure, Balanced)

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

of the X.25 protocol suite, LAPB runs at Layer 2, the Data Link Layer, of the OSI Reference Model.The LAPB frame comprises a header and trailer that encapsulate the packet formed by the X.25 packet layer protocol (PLP) at the Network Layer. The LAPB frame provides a mechanism for transporting packets across a link, ensuring that frames of data are ordered correctly and are free from error. LAPB is a balanced protocol that operates in asynchronous balanced mode (ABM), referring to the fact that the devices have a balanced, rather than a master/slave, relationship. LAPB is a derivative of the High-level Data Link Control (HDLC) protocol, which, in turn, is based on the IBM Synchronous Data Link Control (SDLC) frame. Figure L-1 illustrates the LAPB frame and its component fields.

1

1

1

Variable

2

1

Flag

Address Control

Frame Check

Packet

Flag

Sequence

Header

Trailer

• IS-856 (Interim Standard 856)
• iSCSI (internet Small Computer System Interface)
• iSCSI (internet Small Computer System Interface)
• ISDN Digital Subscriber Line (IDSL)
• ISDN (Integrated Services Digital Network)
• ISDN (Integrated Services Digital Network)
• ISDN modem
• I series
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• ISI (InterSymbol Interference)
• IS (Information Services)
• ISLAN (Integrated Services Local Area Network)
• ISLAN (Integrated Services Local Area Network)
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• IsoEthernet (Isochronous Ethernet)
• ISO/IEC 11801
• ISO (International Organization for Standardization)
• isotropic
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• ITA #2 (International Telegraph Alphabet #2)