BDC5eChapter17 - Chapter 17: Data Link Control and...

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Chapter 17: Data Link Control and Multiplexing Business Data Communications, 5e
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Business Data Communications, 5e 2 Flow Control Necessary when data is being sent faster than it can be processed by receiver Computer to printer is typical setting Can also be from computer to computer, when a processing program is limited in capacity
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Business Data Communications, 5e 3 Error Correction Two types of errors Lost frame Damaged frame Automatic Repeat reQuest (ARQ) Error detection Positive acknowledgment Retransmission after time-out Negative acknowledgment and retransmission
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Business Data Communications, 5e 4 Data Link Control Specified flow and error control for synchronous communication Data link module arranges data into frames, supplemented by control bits Receiver checks control bits, if data is intact, it strips them
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Business Data Communications, 5e 5 High-Level Data Link Control On transmitting side, HDLC receives data from an application, and delivers it to the receiver on the other side of the link On the receiving side, HDLC accepts the data and delivers it to the higher level application layer Both modules exchange control information, encoded into a frame
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Business Data Communications, 5e 6 HDLC Frame Structure Flag: 01111110, at start and end Address: secondary station (for multidrop configurations) Information: the data to be transmitted Frame check sequence: 16- or 32-bit CRC Control: purpose or function of frame I nformation frames: contain user data S upervisory frames: flow/error control (ACK/ARQ) U nnumbered frames: variety of control functions (see p.131)
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Business Data Communications, 5e 7 HDLC Operation Initialization: S-frames specify mode and
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BDC5eChapter17 - Chapter 17: Data Link Control and...

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