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Data Transmission

Data Transmission. Data Transmission: Question: How does data (such as voice, speech etc.) travel from source to destination, Over a long distance? Answer: Data (such as voice, speech etc.) is put over, An electronic signal called, Carrier signal which can,

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Data Transmission

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  1. Data Transmission • Data Transmission: • Question: • How does data (such as voice, speech etc.) travel from source to destination, • Over a long distance? • Answer: • Data (such as voice, speech etc.) is put over, • An electronic signal called, • Carrier signal which can, • Travel and take the data over a long distance from, • Source to destination. • This process of putting/coding the data on the carrier signal is called: • Modulation/Encoding • Modulation means ‘to change/vary something’.

  2. Data Transmission • Modulation: • Types of Data: • Analog Data: • Voice, Speech etc. • Digital Data: • Computer data. • Types of Signals: • Analog Signal: • Wave like signal having properties such as: • Amplitude, Wavelength, Frequency, Oscillations etc. • Digital Signal: • Step like signal having properties such as: • Bit rate, Baud rate etc.

  3. Data Transmission • Categories of Modulation: • ‘Analog Signal’ used to transmit ‘Analog Data’. • Put Analog data on Analog signal. • Example: • Telephone conversation. • Radio broadcast stations. • ‘Analog Signal’ used to transmit ‘Digital Data’. • Put Digital data on Analog signal. • Example: • Computer communication over Telephone lines using Modems. • ‘Digital Signal’ used to transmit ‘Analog Data’. • Put Analog data on Digital signal. • Example: • Voice communication over computer network. • Voice communication through Fiber-optic cable. • ‘Digital Signal’ used to transmit ‘Digital Data’. • Put Digital data on Digital signal. • Example: • Computer network communication.

  4. Analog Signal to transmit Analog Data Amplitude Modulation (AM) Analog Data (Voice) Analog Carrier Signal Output (Modulated Signal)

  5. Analog Signal to transmit Analog Data Amplitude Modulation (AM) Analog Data (Voice) Analog Carrier Signal Output (Modulated Signal)

  6. Analog Signal to transmit Analog Data Frequency Modulation (FM) Analog Data (Voice) Analog Carrier Signal Output (Modulated Signal)

  7. Analog Signal to transmit Analog Data • Amplitude Modulation (AM): • Refers to a change in the, • Height of the carrier signal. • When data is put/encoded on the carrier signal, • The height/amplitude of the signal is changed to indicate appropriate data. • Example: • High peaks in the wave might produce louder sounds (or quieter sounds), while, • Low peaks on the wave might produce a quieter sound (or louder sound). • Used in: • Radio transmission for AM radio stations. • Disadvantage: • Highly susceptible (prone/vulnerable) to noise and interference from external source such as ‘Thunderstorm’.

  8. Amplitude Modulation (AM)

  9. Analog Signal to transmit Analog Data • Frequency Modulation (FM): • Refers to a change in the, • Number of waves of the carrier signal. • When data is put/encoded on the carrier signal, • The frequency of the signal is changed to indicate appropriate data. • Example: • More waves per unit of time might indicate a higher tone (or lower tone) and, • Fewer waves per unit of time might indicate a lower tone (or higher tone). • Used in: • FM radio stations. • Advantage: • More resistant to external interference than Amplitude Modulation (AM). • Unlike an AM radio signal, an FM radio signal would not be interrupted by a passing thunderstorm.

  10. Frequency Modulation (FM)

  11. Analog Signal to transmit Digital Data Amplitude Modulation (AM) / Amplitude Shift Keying (ASK) Digital Data 0 1 1 0 0 0 1 0 1 1 1 Analog Carrier Signal Output (Modulated Signal)

  12. Analog Signal to transmit Digital Data Frequency Modulation (FM) / Frequency Shift Keying (FSK) Digital Data 0 1 1 0 0 0 1 0 1 1 1 Analog Carrier Signal Output (Modulated Signal)

  13. Analog Signal to transmit Digital Data Phase Modulation (PM) / Phase Shift Keying (PSK) Digital Data 0 1 1 0 0 0 1 0 1 1 1 Analog Carrier Signal Output (Modulated Signal)

  14. Analog Signal to transmit Digital Data Differential Phase Shift Keying (DPSK) Digital Data 0 1 1 0 0 0 1 0 1 1 1 Analog Carrier Signal Output (Modulated Signal)

  15. Analog Signal to transmit Digital DataSummary AM / ASK FM / FSK DPSK PM / PSK

  16. Analog Signal to transmit Digital Data • Amplitude Modulation (AM) / Amplitude Shift Keying (ASK) : • Refers to a change in the, • Height/Amplitude of waves of the carrier signal. • When data is put/encoded on the carrier signal, • The height of the signal is changed to indicate appropriate data. • Example: • Highest peak might represent a ‘1’ bit and, • Lowest peak might represent a ‘0’ bit.

  17. Analog Signal to transmit Digital Data • Frequency Modulation (FM) / Frequency Shift Keying (FSK) : • Refers to a change in the, • Number of waves of the carrier signal. • When data is put/encoded on the carrier signal, • The frequency of the signal is changed to indicate appropriate data. • Example: • ‘1’ might be represented by more waves per unit time and, • ‘0’ might be represented by less waves per unit time.

  18. Analog Signal to transmit Digital Data • Phase Modulation (PM) / Phase Shift Keying (PSK) : • Refers to a change in the, • Phase/Direction of the wave of the carrier signal. • When data is put/encoded on the carrier signal, • The phase/direction of the signal is changed to indicate appropriate data. • Neither the amplitude nor the frequency are changed. • Example: • To indicate a ‘1’ bit, wave moves in a specific direction and, • To indicate a ‘0’ bit, the direction of the wave changes to the opposite direction.

  19. Analog Signal to transmit Digital Data • Differential Phase Shift Keying (DPSK) : • Similar to Phase Shift Keying (PSK) except for the fact that, • Signal changes direction only when a ‘1’ bit is detected and, • ‘0’ bit causes no change in the wave.

  20. Digital Signal to transmit Analog Data Analog Data (Speech) Digital Carrier Signal Conclusion: Difficult to directly represent Analog Data using Digital Signal. Analog data can have more values than what Digital can represent.

  21. Digital Signal to transmit Analog Data Pulse Code Modulation (PCM) 0 0 0 0 0 0 1 0 … Analog Data (Speech) Output (Modulated Digital Signal) Sampling Sampled Data Modulation/Encoding 10 Quantization 5 00000010 00000101 00001010 00000101 00000011 10000010 …… 2 Quantized Data Binary Encoding Binary Data 2 5 10 5 3 -2 …

  22. Digital Signal to transmit Analog Data • Pulse Code Modulation (PCM): • Steps: • Sampling: • Continuous analog signal is converted to, • Non-continuous (discrete) signal by, • Taking samples (values) at small time intervals. • To reproduce/rebuild the exact analog signal, number of samples taken should be: • Twice the maximum frequency. (Nyquist Theorem) • Example: • For a telephone call of 4,000 Hz frequency, sampling should occur at: • 4000 x 2 = 8000 samples per second. • Quantization: • Integer values (Digits / Quantities) are assigned to the samples depending on the amplitude of the signal at the instant that it is sampled. • Binary Encoding / Digital Encoding: • Values are converted to binary equivalents. • Modulation: • Binary digits are represented using Digital Signal.

  23. Digital Signal to transmit Analog Data Some other techniques used in the past. Analog Data Pulse Amplitude Modulation (PAM) Pulse Width Modulation (PWM) Pulse Duration Modulation (PDM) Pulse Position Modulation (PPM) Common disadvantage: Do not produce a ‘Pure Digital Signal’ (having only 2 unique states).

  24. Digital Signal to transmit Digital Data Unipolar Coding Digital Data 0 1 0 1 0 0 1 1 0 1 1 1 0 Digital Carrier Signal Output (Modulated Signal)

  25. Digital Signal to transmit Digital Data Polar Coding (NRZ Coding) Digital Data 1 0 0 1 0 1 0 0 0 Digital Carrier Signal Output (Modulated Signal)

  26. Digital Signal to transmit Digital Data Bipolar Coding Digital Data 0 0 1 1 0 1 0 Digital Carrier Signal Output (Modulated Signal)

  27. Digital Signal to transmit Digital Data • Unipolar Encoding: • Polar refers to, • The polarity of a pulse (signal) on the communications line indicating, • Whether it is positive or negative. • So unipolar encoding uses, • Only one voltage level indicating that, • A binary ‘1’ is present and, • Absence of voltage pulse indicates, • A binary ‘0’ bit.

  28. Digital Signal to transmit Digital Data • Polar Encoding: • Uses two voltage levels where, • Positive voltage might represent a ‘1’ bit and, • Negative voltage might represent a ‘0’ bit. • Because the voltage never goes to 0 value, it is also called: • NRZ Encoding. • Non-return to zero

  29. Digital Signal to transmit Digital Data • Bipolar Encoding: • Uses three voltage levels where, • Binary ‘0’ is indicated by zero voltage and, • Binary ‘1’ is indicated by alternative (changing) positive and negative voltages.

  30. Modulation Summary • ‘Analog Signal’ used to transmit ‘Analog Data’. • Amplitude Modulation (AM) • Frequency Modulation (FM) • ‘Analog Signal’ used to transmit ‘Digital Data’. • Amplitude Modulation (AM) / Amplitude-shift keying (ASK) • Frequency Modulation (FM) / Frequency-shift keying (FSK) • Phase Modulation (PM) / Phase-shift keying (PSK) • Differential Phase-shift keying (DPSK) • ‘Digital Signal’ used to transmit ‘Analog Data’. • Pulse Code Modulation (PCM) • Pulse Amplitude Modulation (PAM) • Pulse Width Modulation (PWM) / Pulse Duration Modulation (PDM) • Pulse Position Modulation (PPM) • ‘Digital Signal’ used to transmit ‘Digital Data’. • Unipolar encoding • Polar encoding (NRZ) • Bipolar encoding

  31. Data Transmission • Transmission Direction: • Path/Direction in which data travels or flows on the network. • Types of data flow: • Simplex. • Duplex. • Half-Duplex • Full-Duplex

  32. Transmission Flow/Direction Simplex Transmission Half-Duplex Transmission Full-Duplex Transmission

  33. Transmission Flow/Direction • Simplex Transmission: • Occurs in only one direction and so, • Person/Entity behaving as a source always behaves as a source and, • Person/Entity behaving as a destination always behaves as a destination and hence, • There is no role reversal. • Examples: • Flow of water from a Tap into the Bucket / Rain. • Tap always acts as sender and Bucket always acts as receiver. • Communication from Keyboard to CPU. • Keyboard always behaves as a sender and CPU as a receiver. • Communication from CPU to Monitor. • CPU acts as sender and Monitor acts as receiver. • Radio broadcast from a radio station.

  34. Simplex Transmission

  35. Transmission Flow/Direction • Half-Duplex Transmission: • Data can go in either direction, but, • Only one way at a time. • As a result, • Sender can behave as a receiver and, • Receiver can behave as a sender but, • Not at the same time. • Example: • Very narrow bridge over a river. • Walkie-Talkie / Push-To-Talk systems. • Both users can talk on the radio, but only one at a time. • Computer communication using Modems. • Delay that occurs when the transmission switches from one direction to the other is called, • Modem turnaround time. • In half-duplex transmission, the switch/changeover between the transmissions is so fast that, • It is transparent (not noticeable) to the user.

  36. Half-Duplex Transmission 800MHz 800MHz

  37. Transmission Flow/Direction • Full-Duplex Transmission: • Data can travel in both directions on the communications line, • Simultaneously / At the same time. • In order to accomplish this type of transmission, • Either communications line must have 2 separate transmission paths or, • Physical division. • The entire transmission capacity of the line must be divided between 2 signals that are traveling in opposite directions. • Logical division using the concepts of FDM, TDM etc. • Examples: • 2-lane highway. • Cell-phone transmission. • Disadvantage: • Echo can sometimes be heard in full-duplex transmission and is more common in, • Long-distance calls. • To suppress echo, Telephone companies install devices called: • Echo suppressors.

  38. Full-Duplex Transmission 800MHz 900MHz

  39. Transmission Flow/Direction • Transmission Flow/Direction: • Common example of Simplex, Half-Duplex and Full-Duplex communication is: • Lecture. • Simplex • Only from lecturer to student. • If the lecturer is very strict. • Half-Duplex • From lecturer to student and vice-versa but not at the same time. • If the lecturer wants discipline but not at the cost of liberty. • Full-Duplex • From lecturer to student and vice-versa at the same time. • If the lecturer does not believe in anything called discipline.

  40. Data Transmission • Transmission Modes: • Way/Manner in which the network sends the data. • Types: • Serial Transmission • Parallel Transmission

  41. Transmission Modes A A LSB MSB 1 0 0 0 0 0 1 0 01000001 01000001 Serial Transmission Serial Port / Interface Parallel Port / Interface Receiver Sender Parallel Transmission B B 0 MSB 1 0 01000010 01000010 0 0 0 1 0 LSB

  42. Serial Interface/Port

  43. USB Interface/Port

  44. Parallel Interface/Port

  45. Transmission Modes • Serial Transmission: • Transmits data as individual bits, • With a single bit following another on the transmission line and hence, • Uses a single communications line to transmit the entire data in the form of, • One bit at a time. • At the receiver, • Bits are reassembled to get the data back. • Port/Interface that allows Serial Transmission: • Serial Port • USB (Universal Serial Bus) • Use: • Protocols such as: • SLIP: Serial Line Internet Protocol • PPP: Point-to-Point Protocol

  46. Transmission Modes • Parallel Transmission: • Transmits an entire word/character/byte (composed of several bits) at one time and hence, • Uses multiple lines to send the number of bits required to transmit the entire word at one time. • Ports/Interfaces that allow Parallel Transmission: • Parallel Port • Use: • Different parts inside a computer normally communicate using parallel transmission. • Disadvantage: • More expensive for transmission of data over long distances.

  47. Parallel Transmission Intel 8085 Processor (8-bit) 8 pins

  48. Data Transmission • Synchronization: • Refers to, • The status of sender and receiver during transmission. • Types: • Asynchronous Transmission • Synchronous Transmission

  49. Data Transmission • Asynchronous Transmission: • Sender and Receiver are not in sync during transmission of data. • Sender sends the data without checking the status of the Receiver as to, • Whether the Receiver is online or not. • Also called: • Different-time, Different-place mode. • Examples: • Letter • Email • SMS • Discussion Boards

  50. Data Transmission • Synchronous Transmission: • Sender and Receiver are in sync during transmission of data. • Sender sends the data only after checking the status of the Receiver when, • The Receiver is online. • Also called: • Same-time, Different-place mode. • Examples: • Phone call • Online IM Chat

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