EE450_Discussion7_Fall08

EE450_Discussion7_Fall08 - Discussion#7 EE450 EE450 HDLC...

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Discussion #7 E450 10/08/2008 EE450, 10/08/2008 HDLC Framing Error Detection and Correction Shirin Ebrahimi
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Layer 2 – The Data Link Layer ± We are now going into more of a study of Layer 2 in the OSI layered architecture ± We’ve talked about different inds of Physical Layers Data Link kinds of Physical Layers ± At this point we have a hysical connection Physical physical connection ± How do we start sending ata? data?
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Framing ± Problem: Breaking sequence of bits into a frame ± Must determine first and last bit of the frame ± Typically implemented by network yp y p y adaptors daptor fetches (deposits) frames out ± Adaptor fetches (deposits) frames out of (into) host memory
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Framing (continued) Bits Minicomputer Card Frame
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Bit-Oriented Protocols ± HDLC: High-Level Data Link Control (also SDLC and PPP) it riented synchronous data link layer protocol ± bit-oriented synchronous data link layer protocol developed by the ISO. ± The original ISO standards for HDLC were: ± ISO 0009 — Frame Structure ± ISO 4335 — Elements of Procedure ± ISO 6159 — Unbalanced Classes of Procedure ± ISO 6256 — Balanced Classes of Procedure ± The current standard for HDLC is ISO 13239, which replaces all of those standards. p ± HDLC provides both connection-oriented and connectionless service.
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H igh-level D ata L ink C ontrol DLC can be used for ± HDLC can be used for ± Point to multipoint connections urrently used almost exclusively to ± Currently used almost exclusively to connect one device to another, using what is known as Asynchronous Balanced Mode (ABM). ± It’s totally balanced i.e. no master/slave lationship relationship. ± Each station may initialize, supervise, recover from errors, and send frames at any time. ± The other modes are Normal Response Mode and Asynchronous Response Mode.
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HDLC Framing DLC frames are transmitted over links with no mechanism ± HDLC frames are transmitted over links with no mechanism to mark the beginning or end of a frame.
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This note was uploaded on 10/21/2008 for the course EE 450 taught by Professor Zahid during the Fall '06 term at USC.

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EE450_Discussion7_Fall08 - Discussion#7 EE450 EE450 HDLC...

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