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Chapter 2

Transmission Basics. Chapter 2. The transfer of any kind of information from one location to another. Communication means sending a stream of bits or bytes from one location to another via transmission medium such as copper wire, fiber optics, laser, radio,infra red light, Bluetooth.

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Chapter 2

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  1. Transmission Basics Chapter 2

  2. The transfer of any kind of information from one location to another. Communication means sending a stream of bits or bytes from one location to another via transmission medium such as copper wire, fiber optics, laser, radio,infra red light, Bluetooth. Data transmission

  3. Bit – most basic information unit used in computing & information theory. Single bit is ‘1’/’0’, ‘true/false’,’on/off’. Byte – a series of 8 bits, also called a character. Computer reads & writes information in bits and bytes. Data transmission

  4. Binary table

  5. Signals – electric or electromagnetic representation of data. • Can be coded for security purposes. • Transmitter – converts a message into a signal, which is carried to a receiver by the communication channel. • 2 types of signals ; • Analog Signal • Digital Signal Types of signals

  6. Def : are continuous electrical signals that vary with time & represented by a waveform. • All natural signal around us is of this type. • Waveform is characterized by 4 properties; • Amplitude – measure of wavelength at any given point of time. (Measured in Volt [V]) • Frequency – number of times waveform repeats itself in a second. (Measured in Hertz[Hz] • Wavelength – distance between two corresponding points on a waveform. (Measured in Meter [m]) • Phase – progress of a wave over time in relationship to a fixed point or other wave with same frequency / amplitude. (Measured in degree [degree] in relation to starting point. Analog signal

  7. Analog signal Voltage 5 4 3 2 1 Amplitude 1s 2s 3s -5V

  8. Def : non-continuous & they change in individual steps. • Consists of pulse & digits with discrete levels or values. • Value of pulse constant, but there is an abrupt change from one digit to another. • Have 2 amplitude levels which represents two voltage pulses. (1/0, true/false, high/low etc) • Positive voltage pulse = 1, no pulse = 0 • Computer is a digital device & they work on digital signals. Digital signal 1 1 1 1 amplitude 0 0 0 time

  9. Comparison of digital & analog signals

  10. Def : signal which is transmitted at input & signal received at output does not always match due to transmission flaws over the transmission channel. • Cause of transmission flaws : • Noise • Attenuation • Latency Transmission flaws

  11. Def : unwanted signal which can disturb or harm the communication system. • Common source of noise is electromagnetic interference (EMI) or wave that is emitted from electric carrying cable or electric devices. • Source of EMI – electric motor, power lines, copier, television, lights & machines. • There are 4 types of noises : • Thermal Noise • Induced Noise • Impulse Noise • Crosstalk noise

  12. Thermal Noise – created by the movement / colliasion of the electrons due to heat in a conductor (wire). • Induced Noise – caused by varying magnetic field originated from external circuit or equipment. (engines may also cause this). • Impulse Noise – pulse(s) appearing at the output point of a data line, which is not transmitted at the input point. (Ex; lightning). • Crosstalk – refers to signal affecting another nearby signal Noise

  13. How to eliminate noise ? Use repeater & amplifier Repeater – device that regenerates digital signal. Amplifier – device with amplify or regenerate analog signal. NOISE

  14. Def : a loss of power. • A signal sent via a transmission media, will lose a portion of its power in form of heat or other form of energy. • How to eliminate attenuation?? • Use amplifier attenuation

  15. Also known as delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. Together latency & bandwidth defines speed & capacity of network. latency

  16. Def : is the addition of information/signal to an electronic or optical signal carrier. A device that performs modulation is a modulator. A device that performs the inverse operation which is demodulation is a demodulator. A device that can do both modulation & demodulation is a modem. modulation

  17. Modulation methods: • Amplitude modulation (AM) – the amplitude of voltage applied to the carrier is varied over time. • Frequency modulation (FM) – the frequency of the career waveform in varied in small but meaningful amounts. • Phase modulation (PM) – the natural flow of the alternating current waveform is delayed temporarily. modulation

  18. Def : transmitting multiple signals over a single communication line or computer channel. • 2 common multiplexing techniques: • Frequency Division Multiplexing (FDM) – separates signals by modulating the data onto different carrier frequencies. • Time Division Multiplexing (TDM) – separates signals by interleaving bits one after the other. multiplexing

  19. Serial transmission – transmission of several bits one after another through a single wire. Parallel transmission – multiple wires are used for transmitting bits simultaneously. Types of data transmission

  20. Comparison between serial & parallel transmission

  21. 3 modes of communication; • Simplex • Half-Duplex • Full-Duplex • Simplex • one way communication • Receiver can only receive but can’t reply / resend. • Flow of information is unidirectional, hence rarely used for data communication. • Ex : television, radio Communication modes

  22. Half-duplex • Two way communication but not at the same time. • Ex : walkie-talkies • Full-duplex • Simultaneous two way communication. • Improves the efficiency of communication • Ex : telephone line Communication modes

  23. 2 types of transmission modes: • Asynchronous transmission • Synchronous transmission • Asynchronous transmission • A technique widely used in personal computers to provide connectivity to printers, modems, fax machines etc. • Codes are sent in untimely manner with uneven intervals between characters. • Sending & receiving data is controlled by start & stop bit. Transmission modes

  24. Synchronous transmission • Technique of transmission in which the transmitter & receiver are synchronized. • Codes are sent from transmitting station to receiving station to establish the synchronization. • Data is transmitted in continuous stream. Transmission modes

  25. Comparison between asynchronous & synchronous transmission.

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