Communication Systems and Computer Networks (1404703) PDF

Communication Systems and Computer Networks (1404703) Prepared by: Prof. Shawkat K. Guirguis Professor of Computer Science & Informatics Part 8 2024-11-2...

Communication Systems and Computer Networks (1404703) Prepared by: Prof. Shawkat K. Guirguis Professor of Computer Science & Informatics Part 8 2024-11-25 (c) Prof.Shawkat K. Guirguis 1  THE PHYSICAL LAYER Study of the mechanical, physical, electrical and timing properties Theoretical analysis of data transmission Cover three kinds of transmission media: 1. Guided, 2. Wireless 3. Satellite 2024-11-25 (c) Prof. Shawkat K. Guirguis 2  THE THEORETICAL BASIS FOR DATA COMMUNICATION f(t) is the voltage or current function being transmitted Being a function it can be mathematically manipulated Fourier Analysis is one of the most important analysis techniques A periodic function can be represented by an infinite number of sines and cosines (see next figure) A function can be reconstructed from its harmonics knowing T. Signals can be analyzed and dominant harmonics only can be considered. Analysis is very important in determining proper sampling of a signal 2024-11-25 (c) Prof. Shawkat K. Guirguis 3  Fourier Series A Fourier series is a representation of a function in terms of a summation of an infinite number of harmonically-related sinusoids with different amplitudes and phases. The amplitude and phase of a sinusoid can be combined into a single complex number, called a Fourier coefficient. The Fourier series is a periodic function. So it cannot represent any arbitrary function. It can represent either: (a) a periodic function, or (b) a function that is defined only over a finite-length interval; the values produced by the Fourier series outside the finite interval are irrelevant. Fourier Series  Bandwidth-Limited Signals Key words: rms amplitude and relation to power Bandwidth (depend on construction, thickness and length of medium) Cutoff frequency (fc) See next figure (effect of low bandwidth) 2024-11-25 (c) Prof. Shawkat K. Guirguis 8  Bandwidth-Limited Signals A binary signal and its root-mean-square Fourier amplitudes. (b) – (c) Successive approximations to the original signal. 2024-11-25 (c) Prof. Shawkat K. Guirguis 9  Bandwidth-Limited Signals (2) (d)– (e) Successive approximations to the original signal. 2024-11-25 (c) Prof. Shawkat K. Guirguis 10  Bandwidth-Limited Signals (3) Relation between data rate and harmonics. 2024-11-25 (c) Prof. Shawkat K. Guirguis 11  The Maximum Data Rate of a Channel (Read) Shanon states that the maximum data rate of a noisy channel whose bandwidth is H Hz, and signal to noise ratio S/N: Max # of bits/sec= H log2 ( 1 + S/N) 2024-11-25 (c) Prof. Shawkat K. Guirguis 12  1. GUIDED TRANSMISSION MEDIA Each media is selected according to bandwidth, delay, cost and ease of installation Magnetic Media (Skip for irrelevance) Twisted Pair Coaxial Cable Fiber Optics 2024-11-25 (c) Prof. Shawkat K. Guirguis 13  Twisted Pair Consists of two insulated copper wires, 1mm thick. Twisting is done to eliminate antenna effect of parallel lines Most common use in telephones Can run several Kms without amplification For longer distances, repeaters are needed 2024-11-25 (c) Prof. Shawkat K. Guirguis 14  Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP. 2024-11-25 (c) Prof. Shawkat K. Guirguis 15  Twisted Pair (cont.) Several twisted pairs are bundled in protective shields Used to transmit both analog and digital signals Bandwidth depends on thickness and length Several Mb/s can be achieved Used extensively because of low cost Category 3,5,6,7 etc. defines how many twists/cm More twists reduce crosstalk & better quality signals over long distances Speeds up to 600 MHz Typically called UTP (Unshielded Twisted Pair) 2024-11-25 (c) Prof. Shawkat K. Guirguis 16  Coaxial Cable It has better shielding than UTP Span longer distances with higher speeds Can have 1GHz bandwidth 2024-11-25 (c) Prof. Shawkat K. Guirguis 17  Coaxial Cable A coaxial cable. 2024-11-25 (c) Prof. Shawkat K. Guirguis 18  Fiber Optics It is an ultra-thin fiber of glass Light is converted to electrical signals Theoretically 50,000 Gbps with almost zero error rate Ability may be only 10Gbps!! Why? Some leaking might happen 2024-11-25 (c) Prof. Shawkat K. Guirguis 19  Fiber Optics (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection. 2024-11-25 (c) Prof. Shawkat K. Guirguis 20  Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers. 2024-11-25 (c) Prof. Shawkat K. Guirguis 21  Fiber Cables (2) A comparison of semiconductor diodes and LEDs as light sources. 2024-11-25 (c) Prof. Shawkat K. Guirguis 22