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Data Link Control Protocols

HDLC. Accepts user data from higher level software and delivers across link to another deviceOn other side HDLC accepts user data and send it to applicationBoth HDLC modules exchange control information to provide:Flow controlError control. HDLC. FlagUsed for synchronizationBeg and end of fra

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Data Link Control Protocols

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    1. Data Link Control Protocols Interface standards provide means for which a strem of data can be transmitted but do not include function of error control and flow control A data link control protocol handles error control and flow control Examples of data link protocols HDLC – High Level Data Link Control LAPB Connect devices to packet switched networks LAPF Frame relay

    2. HDLC Accepts user data from higher level software and delivers across link to another device On other side HDLC accepts user data and send it to application Both HDLC modules exchange control information to provide: Flow control Error control

    3. HDLC Flag Used for synchronization Beg and end of frame Address Address of secondary stations Point to point or multidrop Control Identifies purpose and function of frame Information User Data Frame Check Sequence 16 or 32 bit CRC

    4. HDLC Information Frames I frame Carries user data Can also carry flow control and error control Supervisory Frames S Frames Flow control and error control Unnumbered frames Link set – up and disconnection No acknowledgement information

    5. HDLC in Action Initialization Specifies which of 3 modes to operate in Specifies 3 or 7 bit sequence If B accepts B sends unnumbered acknowledgement If rejected B sends disconnected mode (DM) A can send a disconnect (DISC) and B acknowledges with unnumbered acknowledgement Because of fault or instruction from application software

    6. HDLC in Action

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