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FILES, DATA, AND SIGNALS

FILES, DATA, AND SIGNALS. FILE HAMLET. TXT USER DATA INTERNAL y e a , b REPRESENTATION 01011001 01100101 01100001 00101100 00100000

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FILES, DATA, AND SIGNALS

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  1. FILES, DATA, AND SIGNALS • FILE HAMLET. TXT • USER DATA • INTERNAL y e a , b • REPRESENTATION 01011001 01100101 01100001 00101100 00100000 • OF USER DATA f r o m b • 01100110 01110010 01101111 01101101 00100000 • Internal representation of information stored in n-bit entities corresponding to a particular character code (e.g., ASCII is shown here). Yea, from the table of my memory I’ll wipe away all trivial fond records

  2. FILES, DATA, AND SIGNALS (cont.) SIGNAL 1 0 0 1 1 0 1 0 1 0 1 0 0 1 1 0 1 0 0 0 1 10 0 0 1 10 1 0 0 LSB LSB LSB LSB • SIGNAL – External representation of user data -- Mapping of bits to a signal depends only on choice of implementer. NonReturn to Zero-Level (NRZ-L) shown, but other signaling types are possible.

  3. PARALLEL TRANSMISSION , y e a b f r o m Receiver Transmitter MSB LSB CLOCK DTE DTE t0 t1 t2 t3 t4 t5 t6 t7 T8

  4. t0 t1 0 1 1 0 1 1 1 1 SKEW SKEW: The arrival of bits from the same character at different times may lead to erroneous reception.

  5. SERIAL VS. PARALLEL TRANSMISSION PARALLEL SERIAL CPU-peripheral, internal to computer. Relative short distance DTE – DTE. Longer distances. APPLICATIONS Long distances possible. Easier to implement. Device-independent. Very high throughput. Matches internal architecture. ADVANTAGES Extra cable, connectors, Amplifiers, and Clock add expense. Skew limits distance. Relatively low speeds. Parallel-to-Serial Conversion required. DISADVANTAGE

  6. ASYNCHRONOUS TRANSMISSION STOP BIT y e START BIT 1 0 0 1 1 0 1 0 1 0 1 0 0 1 1 0 FRAMING LSB MSB FRAMING • Asynchronous transmission: • Timing of each bit is specified within a character • Inter-character time is non-uniform • Each character must be framed

  7. y e a 1 0 0 1 1 0 1 0 1 0 1 0 0 1 1 0 1 0 0 0 0 1 1 0 t LSB MSB SYNCHRONOUS TRANSMISSION • Characters, within a block, are sent contiguously • Each block is framed

  8. DATA BITS STOP INTERVAL START BIT MARK SPACE TIME LEAST SIGNIFICANT BIT ASYNCHRONOUS CHARACTER FORMAT LINE IDLE • Transmitter and receiver must agree on: • Number of data bits per character • Length of a bit time • Length of the stop interval • Signal level • Order of bit transmission • Character code

  9. SYNCHRONOUS MESSAGE FORMAT SYNC CHAR (s) MESSAGE TRAILER MESSAGE HEADER DATA BLOCK OR FRAME • All data characters sent as part of a continuous transmission block (frame) • Transmitter and receiver must agree on: -- Transmission format -- Length of a bit time -- Signal levels -- SYNC characters -- Size and content of header and trailer

  10. ASYNCHRONOUS VS. SYNCHRONOUS TRANSMISSION ASYNCHRONOUS SYNCHRONOUS Between a terminal and computer or between low-cost computer – and - computer High-speed Device interconnection. APPLICATIONS Simple to implement. Low cost. Clock resynchronizes with each character. High throughput. High line efficiency ADVANTAGES Error detection protocol required. Self-clocking signaling Technique required. High cost. Low line efficiency Low speed (<20,000 bps) DISADVANTAGES

  11. HAMLET.TXT CREATED BY USER AT HOST A CHARACTER CODE INTERNAL REPRESENTATION OF FILE CHOICE OF SIGNAL EXTERNAL REPRESENTATION OF DATA PARALLEL TRANS. SERIAL TRANS. SYNCHRONOUS ASYNCHRONOUS  ADDITIONAL AGREEMENTS STILL REQUIRED A FILE TRANSFER HAMLET.TXT Host B Host A TRANSMISSION LINK  FILE TRANSFER: THE STEPS IDENTIFIED IN THIS UNIT

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