06-DigitalDataCommunications

06-DigitalDataCommunications - William Stallings Data and...

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1 William Stallings Data and Computer Communications 7th Edition Chapter 6 Digital Data Communications Techniques
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2 Asynchronous and Synchronous Transmission Timing problems require a mechanism to  synchronize the transmitter and receiver Two solutions Asynchronous – each character is treated  independent Synchronous – data sent in formatted blocks with  some form of synchronization
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3 Asynchronous Data transmitted on character at a time 5 to 8 bits Timing only needs maintaining within each  character (e.g. the bits) Resynchronize with each character
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4 Asynchronous (diagram)
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5 Asynchronous - Behavior In a steady stream, interval between characters  is uniform (length of stop element) In idle state, receiver looks for transition 1 to 0 Then samples next seven intervals (char length) Then looks for next 1 to 0 for next char Simple Cheap Overhead of 2 or 3 bits per char (~20%) Good for data with large gaps (keyboard)
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6 Synchronous - Bit Level Block of data transmitted without start or stop  bits Clocks must be synchronized Can use separate clock line
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06-DigitalDataCommunications - William Stallings Data and...

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