The transmission media


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This presentation is about transmission media which include guided and unguided medium.

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The transmission media

  2. 2.  On any network, the various entities must communicate through some form of media.  Just as humans can communicate through telephone wires or sound waves in the air, computers can communicate through cables, light, and radio waves. • Transmission media enables computers to send and receive messages but do not guarantee that the messages will be understood. 2
  3. 3.  Communication is possible only if information is encoded in a signal, and the signal is carried on a transmission ,the characteristics of the signal and of the medium both determine the quality of the communication medium.  There are two main groups of transmission media, namely the guided medium and the unguided medium (wireless medium). 3
  4. 4.  For the guided medium, there is a physical path (such as a cable) for electromagnetic wave propagation.  For the unguided medium, however, the electromagnetic wave is transmitted through air, water, or vacuum. 4
  5. 5. CHARACTERISTICS  A good transmission medium should provide communication with good quality at long distance.  For voice communication, quality of communication is determined by the voice quality.  For data communication, however, the quality of communication is mainly determined by the effective data rate of communication. 5
  6. 6.  Communication bandwidth of the medium  Interference  The transmission impairments 6
  7. 7.  The bandwidth of a medium determines the signal frequencies that can be carried in the medium.  A wide bandwidth, or broadband, usually allows communication at a higher data rate. 7
  8. 8.  Attenuation  Distortion during signal propagation  Noises. 8
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  10. 10. Transmission Media Guided Media Twisted Pair Cable Coaxial Cable Unguided Media FiberOptic Cable Radio Microwave Satellite 10
  11. 11. Guided media includes everything that ‘guides’ the transmission. That usually takes the form of some sort of a wire. Usually copper, but can also be optical fibre. 11
  12. 12. • A transmission medium consisting of pairs of twisted copper wires. • We can transmit 1 Mbps over short distances (less than 100m). • They are mainly used to transmit analog signals, but they can be used for digital signals. 12
  13. 13. The twisted pair cable can be broadly categorized into the following two types • Shielded Twisted Pair (STP) Cable the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference • Unshielded Twisted Pair (UTP) Cable each wire is insulated with plastic wrap, but the pair is encased in an outer covering 13
  14. 14. STP (shielded twisted pair) UTP (unshielded twisted pair) 14
  15. 15. • In its simplest form, coaxial consists of a core made of solid copper surrounded by insulation, a braided metal shielding, and an outer cover. • A transmission medium consisting of thickly insulated copper wire, which can transmit a large volume of data than twisted wire. 15
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  17. 17. • Optical fiber consists of a glass core, surrounded by a glass cladding with slightly lower refractive index. • In most networks fiber-optic cable is used as the high-speed backbone, and twisted wire and coaxial cable are used to connect the backbone to individual devices. 17
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  19. 19. Unguided media is still ‘media’ (stuff that signal travels though). The trick is that the media is usually not directional, like air, space, etc. Because the effect is usually much wider than with guided media, there have been a lot of regulation, licensing, and standardization of transmissions via unguided media. 19
  20. 20. • Wireless transmission that sends signals through air or space without any physical wire. • Common uses of wireless data transmission include pagers, cellular telephones, microwave transmissions, communication satellites, mobile data networks, personal digital assistants, television remote controls. 20
  21. 21. Wireless Transmission Radio Wave Microwave Infrared 21
  22. 22. Radio waves are used for multicast communications, such as radio and television, and paging systems. They can penetrate through walls. Highly regulated. Use Omni directional antennas Omni directional antenna 22
  23. 23. Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Higher frequency ranges cannot penetrate walls. Use directional antennas - point to point line of sight communications Infrared signals can be used for shortrange communication in a closed area using line-of-sight propagation. 23
  24. 24. Key is the antenna Role of antenna – conversion between electrical signals and airborne signals Transmission – antenna gets electrical signals, and radiates airborne energy into the medium; i.e., air Reception – antenna receives airborne waves from the surrounding medium and converts them to electrical signals Every wireless system MUST have antennas. Antenna design is related to three major considerations: •Frequency to be transmitted •Direction of transmission •Power needed for transmission 24
  25. 25.  It is inexpensive and already is in use.  Twisted wires are slow, high-speed transmission causes interference (crosstalk).  Limiting factors: skin effect & radiation effect. 26
  26. 26.  It is often used in place of twisted wire for important links in a network because it is a faster.  More interference-free transmission medium (speed: 200 megabits per second).  Coaxial cable is thick, is hard to wire in many buildings. It does not support analog conversations. 27
  27. 27.  Optical fibers are faster, lighter, and suitable for transferring large amount of data.  Fiber-optic cable is more difficult to work with, more expensive.  Its difficult to install them. 28
  28. 28. • Optical fiber cable differs from both these transmission media in that it carries the transmitted information in the form of a fluctuating beam of light in a glass fiber. • Light transmission has much wider bandwidth, thus enabling the transmission rate of hundreds of megabits per second. 29
  29. 29. • Optical transmission is immune to electromagnetic interference and crosstalk. While others are immune to interference. • Optical fibers have less loss of signal strength than copper, after every 30 miles we need to use a repeater, whereas in copper, we should insert repeaters at an interval of 2.8 miles . • Optical fiber is more secure, no easy tapping on the cable, like in copper. • But optical fibers are more expensive than other two cables. 30
  30. 30. Bandwidth: The difference between the lowest and highest frequency signals that can be transmitted across a transmission line or communication system. Interference: The distortion on the signal in transmission due to unwanted signals from outside sources. 31
  31. 31. Transmission Impairments: Attenuation, distortion, or noises that will degrade the signal quality during transmission. Attenuation: The loss of a signal’s energy when the signal is transmitted across a medium. Signal Distortion: Any change in a signal during signal transmission. 32
  32. 32. Noises: Random signals that can be picked up during signal transmission and result in degradation or distortion of data. Trunk Circuits: The communication circuits between two switching offices. 33
  33. 33.  In summary, transmission media are essential for communication systems. Signals that carry information can be transmitted on a transmission medium for communication purposes. The transmission characteristics of the medium in use are important because they directly affect the communication quality. Since different types of transmission media have different transmission characteristics and costs, they are used in different (and the most suited) applications. 34
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