![[Data]
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Data is a collection of facts, such as numbers, words, measurements,
observations or even just descriptions of things.
• Analog
• Digital](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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- 1. NETWORK PHYSICAL LAYER 1 3 Prepared by: Mir Omranudin Abhar Email : MirOmran@Gmail.com Fall ,2019
- 2. [Data] 2 Data is a collection of facts, such as numbers, words, measurements, observations or even just descriptions of things. • Analog • Digital
- 3. Data[ Analog ] 3 Analog Data (Information that is continuous, Analog data take on continuous values). Analog data, such as the sounds made by a human voice, take on continuous value.
- 4. Data[Digital] 4 Digital Data (Information that will have discrete states,They can take on discrete values). For example, data are stored in computer memory in the form of 0s and 1s.
- 5. [Signal] 5 A signal is an electrical or electromagnetic current that is used for carrying data from one device or network to another. • Analog • Digital
- 6. Signal [Digital & Analog ] 6 Analog Signals 1. Continuous 2. Infinte range of values Digital Signals 1. Discrete 2. Finite range of values
- 7. Periodic and Nonperiodic Signals 7
- 8. Periodic and Nonperiodic Signals 8 In data communications, we commonly use periodic analog signals and nonperiodic digital signals.
- 9. Analog Periodic Signals 9 Simple Periodic Signals Composite Periodic Signals
- 10. Sine wave 10 A sine wave can be represented by three parameters: • Peak amplitude • Frequency • Phase
- 11. Sine Wave [Peak Amplitude] 11 The peak amplitude of a signal is the absolute value of its highest intensity, proportional to the energy it carries. For electric signals, peak amplitude is normally measured in volts.
- 12. Sine Wave [Period and Frequency] 12 • Period refers to the amount of time, in seconds, a signal needs to complete 1 cycle. • Frequency refers to the number of periods in I s. • Period is the inverse of frequency, and frequency is the inverse of period.
- 13. Sine Wave [Period and Frequency] 13 𝑇 = 1 𝑓 , 𝐹 = 1 𝑇
- 14. Sine Wave [Period and Frequency] 14 Period is formally expressed in seconds. Frequency is formally expressed in Hertz (Hz), which is cycle per second.
- 15. Sine Wave [Phase] 15 The term phase describes the position of the waveform relative to time 0. A sine wave with a phase of 0° starts at time 0 with a zero amplitude. The amplitude is increasing.
- 16. Sine Wave [Phase] 16 A sine wave with a phase of 90° starts at time 0 with a peak amplitude. The amplitude is decreasing. A sine wave with a phase of 180° starts at time 0 with a zero amplitude. The amplitude is decreasing.
- 17. Sine Wave [Wave Length] 17 wavelength is the spatial period of a periodic wave the distance over which the wave's shape repeats.
- 18. [Time Domain & Frequency Domain] 18 The Time-domain plot shows changes in signal amplitude with respect to time (it is an amplitude-versus-time plot). A Frequency-domain plot is concerned with only the peak value and the frequency.
- 19. [Time Domain & Frequency Domain] 19
- 20. [Composite signal ] 20 A composite signal is a bus signal.
- 21. [Bandwidth] 21 The range of frequencies contained in a composite signal is its bandwidth. The bandwidth is normally a difference between two numbers. For example, if a composite signal contains frequencies between 1000 and 5000, its bandwidth is 5000 - 1000, or 4000.
- 22. [Bandwidth] 22
- 23. [Bandwidth] 23 If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is its bandwidth?
- 24. [Digital Signals] 24 In addition to being represented by an analog signal, information can also be represented by a digital signal. For example, a 1 can be encoded as a positive voltage and a 0 as zero voltage. A digital signal can have more than two levels. In this case, we can send more than 1 bit for each level
- 26. [Digital Signals] 26 A digital signal has eight levels. How many bits are needed per level?
- 27. [Digital Signals] 27 Assume we need to download text documents at the rate of 100 pages per minute. What is the required bit rate of the channel? Solution A page is an average of 24 lines with 80 characters in each line. If we assume that one character requires 8 bits, the bit rate is
- 28. [Digital Signals] 28 The time and frequency domains of periodic and nonperiodic digital signals
- 29. [Digital Signals]-[Baseband transmission] Baseband transmission means sending a digital signal over a channel without changing the digital signal to an analog signal. Baseband transmission requires low pass channel for transmission. A low pass channel is a channel whose bandwidth starts from zero. 29
- 31. [Digital Signals]-[Broadband transmission] Broadband transmission means sending a digital signal over a channel after changing the digital signal to analog signal. Broadband transmission can use bandpass channel. A bandpass channel is a channel whose bandwidth does not start from zero. 31
- 33. [Digital Signals]-[Broadband transmission] 1. A bandpass channel is more available than a lowpass channel. 2. If the available channel is bandpass, we cannot send the digital signal directly to the channel, it must be converted to an analog form before transmission. 33
- 34. Approximation of a digital signal 34
- 35. Approximation of a digital signal 35
- 36. [ Transmission Impairment ] 36 Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received. Three causes of impairment are attenuation, distortion, and noise.
- 37. [ Transmission Impairment ] 37
- 38. [Transmission Impairment][Attenuation] 38 • Attenuation means a loss of energy. • To compensate for this loss, amplifiers are used to amplify the signal.
- 39. [Transmission Impairment][Distortion] 39 • Distortion means that the signal changes its form or shape. Distortion can occur in a composite signal made of different frequencies. Each signal component has its own propagation speed.
- 40. [Transmission Impairment][Noise] 40 • Noise is unwanted electrical or electromagnetic energy that degrades the quality of signals and data.
- 41. [Transmission Impairment][Noise] 41 Type of Noise: • Thermal Noise is the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter. • Induced Noise comes from sources such as motors and appliances. These devices act as a sending antenna, and the transmission medium acts as the receiving antenna.
- 42. [Transmission Impairment][Noise] 42 Type of Noise: • Crosstalk is the effect of one wire on the other. One wire acts as a sending antenna and the other as the receiving antenna. • Impulse noise is a spike (a signal with high energy in a very short time) that comes from power lines, lightning, and so on.