Data and Computer Communications by William Stallings Eighth Edition

1. Transmission Media Data and Computer Communications by William Stallings Eighth Edition Click to edit Master subtitle style Chapter 4 Networks and Communication Department

2. Overview • transmission medium: is the physical path between transmitter and receiver. • transmission media can be classified as : • 1- guided media- wire : • electromagnetic waves are guided along a solid medium, such as copper twisted pair, copper coaxial cable, and optical fiber • 2- unguided media – wireless: • wireless transmission occurs through the atmosphere, outer space, or water.

3. Overview • characteristics and quality determined by medium and signal • in unguided media - bandwidth produced by the antenna is more important • in guided media - medium is more important • key concerns are data rate and distance

4. Design Factors 1.Bandwidth higher bandwidth gives higher data rate 2.transmission impairments eg. attenuation, limit the distance. For guided media, twisted pair generally suffers more impairment than coaxial cable, which in turn suffers more than optical fiber.

5. Design Factors 3.Interference Interference from competing signals in overlapping frequency bands can distort or wipe out a signal. Interference is of particular concern for unguided media. For guided media, interference can be caused by emanations from nearby cables. For example, twisted pairs . 4.number of receivers in guided media -in guided media -each attachment introduces some attenuation and distortion on the line, limiting distance and/or data rate . -more receivers (multi-point) introduces more attenuation, limiting distance and data rate.

6. Electromagnetic Spectrum

7. Frequency Range Typical Attenuation Typical Delay Repeater Spacing Twisted pair (with loading) 0 to 3.5 kHz 0.2 dB/km @ 1 kHz 50 µs/km 2 km Twisted pairs (multi-pair cables) 0 to 1 MHz 0.7 dB/km @ 1 kHz 5 µs/km 2 km Coaxial cable 0 to 500 MHz 7 dB/km @ 10 MHz 4 µs/km 1 to 9 km Optical fiber 186 to 370 THz 0.2 to 0.5 dB/km 5 µs/km 40 km Transmission Characteristics of Guided Media

8. Twisted Pair • physical description: • Atwisted pair consists of two insulated copper wires arranged in a regular spiral pattern. • The twisting tends to decrease the crosstalk interference between adjacent pairs in a cable. • Twisted pair is much less expensive than the other • easier to work with.

9. Twisted Pair • Application: • Most common medium • • Telephone network • • Between house and local exchange • -Within buildings . • • For local area networks (LAN)

10. Twisted Pair • Transmission Characteristics: • analog • needs amplifiers every 5km to 6km • digital • can use either analog or digital signals • needs a repeater every 2-3km • limited distance • limited bandwidth (1MHz) • limited data rate (10 to 100MHz) • susceptible to interference and noise

11. Unshielded vs Shielded TP Twisted pair comes in two varieties: • unshielded Twisted Pair (UTP) • ordinary telephone wire • cheapest • easiest to install • suffers from external Electromagnetic interference (EMI) • shielded Twisted Pair (STP) • metal braid or sheathing that reduces interference • more expensive • harder to handle (thick, heavy)

12. UTP Categories Cat 3 (up to 16 MHz) — Twist length of 7.5 cm to 10 cm Cat 5 (up to 100MHz) — Twist length 0.6 cm to 0.85 cm — Tighter twist -> more expensive, But better performance Cat 5E (Enhanced), Cat 6 & Cat 7

13. Coaxial Cable • physical description: • like twisted pair, consists of two conductors. • It consists of a hollow outer cylindrical conductor that surrounds a single inner wire conductor • Coaxial cable can be used over longer distances.

14. Coaxial Cable • Application: • • Television distribution • • Long distance telephone transmission • • Short distance computer systems links • • Local area networks

15. Coaxial Cable • Transmission Characteristics: • Coaxial cable is much less susceptible to interference and crosstalk • than twisted pair • Coaxial cable is used to transmit both analog and digital signals. • -analog signals • amplifiers every few km • closer if higher frequency • up to 500MHz • -digital signals • repeater every 1km • closer for higher data rates

16. Optical Fiber physical description: An optical fiber is a thin (2 to 125 µm), flexible medium capable of guiding an optical ray. Various glasses and plastics can be used to make optical fibers

17. Optical Fiber Application: • Long-haul trunks • Rural exchange trunks • LANs

18. Optical Fiber • Benefits: • greater capacity • data rates of hundreds of Gbps • smaller size & weight • lower attenuation than for coaxial cable or twisted pair • electromagnetic isolation • greater repeater spacing

19. Optical Fiber • Transmission Characteristics: • uses total internal reflection to transmit light • can use several different light sources: • Light Emitting Diode (LED) • cheaper, lasts longer • Injection Laser Diode (ILD) • more efficient, has greater data rate

20. Optical Fiber Transmission Modes There are three fundamental types of fiber optic cable in use: step-indexmultimode Light from a source enters the cylindrical glass or plastic core. Rays at shallow angles are reflected and propagated along the fiber. variety of angles will reflect. With multimode transmission, multiple propagation paths exist, each with a different path length 2. graded-index multimode light in the core curves helically because of the graded index, reducing its travel distance. Graded-index fibers are often used in local area networks. 3. single-mode there is a single transmission path with single-mode transmission. Single-mode is typically used for long-distance applications, including telephone and cable television

21. Optical Fiber Transmission Modes

22. Difference between Guided Media

23. Wireless Transmission techniques • Microwave • Frequency :2GHz to 40GHz • Used for point to point communication • Used for satellite communication • Radiowave • omnidirectional • 30MHz to 1GHz Infrared wave • Used for local point-to-point and multipoint applications • 3x10^11Hz to 2x10^14 Hz

24. Antennas • Electrical conductor used to radiate or collect electromagnetic energy • -transmission antenna • radio frequency energy from transmitter • converted to electromagnetic energy by antenna • radiated into surrounding environment • -reception antenna • electromagnetic energy impinging on antenna • converted to radio frequency electrical energy • fed to receiver • -Same antenna is often used for both purposes

25. Types of Antenna • 1- Horn antenna • 2-Dish antenna

26. Wireless propagation methods • 1-Ground propagation • Follows contour of earth • This effect found in freq below 2MHz • Example :AM radio

27. Wireless propagation methods • 2-Sky propagation • Signal reflected from ionosphere layer of upper atmosphere • Frequency from 2 to 30 MHz • Useful for long distance communication • Example : BBC world service, Voice of America

28. Wireless propagation methods • 3-Line of sight propagation • Point to point • Frequency above 30Mhz communication • Example : satellite ,TV

29. Terrestrial Microwave • Physical description: • The most common type of microwave . • used for: • 1- long haul telecommunications • 2- short point-to-point links • line of sight transmission • use a parabolic dish to focus a narrow beam onto a receiver antenna • an alternative to coaxial cable or optical fiber • requires far fewer amplifiers or repeaters than coaxial cable over the same distance

30. Terrestrial Microwave • Transmission characteristic: • At higher frequency more attenuation • Attenuation increase with rainfall

31. Satellite Microwave • Satellite is relay station • Used to link two or more earth stations • Satellite communication configuration: • 1-Point to Point Link • 2-Broadcast Link

32. Satellite Point to Point Link

33. Satellite Broadcast Link

34. Broadcast Radio • use broadcast radio, 30MHz - 1GHz, for: • FM radio • is omnidirectional • Communication is line of sight • Can penetrate walls • Less sensitive to rainfall • suffers from multipath interference

35. Infrared • infrared light • within line of sight (or reflection) • are blocked by walls, Thus the security and interference problems encountered in microwave systems are not present. • typical uses • TV remote control

36. Refraction • velocity of electromagnetic wave is a function of density of material C= 3 x 108 m/s in vacuum, less in anything else • When an electromagnetic wave moves from a medium of one density to a medium of another density, • its speed changes. • The effect is to cause a bending of the direction of the wave. • Wavelength get smaller

37. Refraction • Index of refraction (refractive index) is: • n=sin(incidence)/sin(refraction) • also n= C/V

38. Summary • looked at data transmission issues • frequency, spectrum & bandwidth • analog vs. digital signals • transmission impairments