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Transmission Medium.pptx
- 1. Computer Communication and Networks(CSC7303) DEPARTMENT OF COMPUTER SCIENCE, Bayero University, Kano. 1 A. A. Datti Lecture 3: Transmission Medium
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- 3. Bayero University ,Kano CSC7307 Computer Communication & Networks Transmission Media A transmission medium can be broadly defined as Physical path between transmitter and receiver For example, the transmission medium for two people having a dinner conversation is the air , For a written message, the transmission medium might be a mail carrier, a truck, or an airplane 3
- 4. Bayero University ,Kano CSC7307 Computer Communication & Networks Transmission Media Transmission media are actually located below the physical layer and are directly controlled by the physical layer. 4
- 5. Bayero University ,Kano CSC7307 Computer Communication & Networks Transmission Media In data communications the transmission medium is usually free space, metallic cable, or fiber-optic cable. The information is usually a signal that is the result of a conversion of data from another form. In telecommunications, transmission media can be divided into two broad categories: guided and unguided. In guided (wired)transmission media waves are guided along a solid medium such as copper twisted pair, copper coaxial cable or optical fiber. Unguided (wireless ) media provides a means for transmitting electromagnetic signals through air but do not guide them 5
- 6. Bayero University ,Kano CSC7307 Computer Communication & Networks Transmission Media 6
- 7. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted-pair cable
- 8. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Cable A twisted pair cable consists of two insulated copper wires arranged in a regular spiral pattern. Typically ,a number of pairs are bundled together into a cable by wrapping them in a tough protective sheath. What is the need for twisting and why not just put two wires as it is? The need for twisting arises because of a phenomenon called crosstalk. 8
- 9. Bayero University ,Kano CSC7307 Computer Communication & Networks Why Twisting ? Twisting decreases crosstalk interference between adjacent pairs in a cable If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relative to the noise or crosstalk sources One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference. The receiver uses the difference between the two. This results in a difference at the receiver. By twisting the pairs, a balance is maintained 9
- 10. Bayero University ,Kano CSC7307 Computer Communication & Networks Why Twisting ? Tighter twisting provides much better performance , but also increases cost For example, suppose in one twist, one wire is closer to the noise source and the other is farther; in the next twist, the reverse is true This means that the receiver, which calculates the difference between the two, receives no unwanted signals. The unwanted signals are mostly canceled out. 10
- 11. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Category 11
- 12. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Category There are several categories of twisted pair of wire. Cat 1 cable has very low bandwidth and we can send data at the rate of about 100 Kbps it is commonly used for analog transmission and primarily used in telephone systems telephone networks. Cat 2 cable has a lower bandwidth less than 2 MHz and you can use data rate of up to 2 Mbps. It can be used for analog transmission as well as for low bandwidth digital signal transmission. 12
- 13. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Category Cat 3 which has a bandwidth of 16 MHz allows data rates of 10 Mbps and this can be used not only for analog data communication but it is also commonly used for digital data communication Particularly it is used in Local Area Networks Cat 4 has 20 MHz bandwidth with data rate of 20 Mbps. It is also primarily used in digital data transmission, digital signal transmission and commonly used in Local Area Networks. 13
- 14. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Category Category 5 having bandwidth of 100 MHz and has 100 Mbps. It also uses digital data transmission particularly in Local Area Networks. Category 6 and category 7 are also available nowadays. The two commonly used categories are Cat 3 (Up to 16MHz) and Cat 5 (Up to 100MHz ) Cat 3 has 3-4 twists per ft ,Cat 5 has 3-4 twists per inch 14
- 15. Bayero University ,Kano CSC7307 Computer Communication & Networks Twisted Pair Wires Two varieties STP (shielded twisted pair) the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference UTP (unshielded twisted pair) each wire is insulated with plastic wrap, but the pair is encased in an outer covering CS/IS 465 - Data Communications and Networks 15
- 16. Bayero University ,Kano CSC7307 Computer Communication & Networks UTP and STP 16
- 17. Bayero University ,Kano CSC7307 Computer Communication & Networks UTP 17
- 18. Bayero University ,Kano CSC7307 Computer Communication & Networks UTP 18
- 19. Bayero University ,Kano CSC7307 Computer Communication & Networks STP 19
- 20. Bayero University ,Kano CSC7307 Computer Communication & Networks UTP connector 20
- 21. Bayero University ,Kano CSC7307 Computer Communication & Networks Coaxial Cable Coaxial cable carries signals of higher frequency ranges than those in twisted- pair cable It has a central core conductor of solid or stranded wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of the two The outer metallic wrapping serves both as a shield against noise and as the second conductor The outer conductor is also enclosed in an insulating sheath, and the whole cable is protected by a plastic cover 21
- 22. Bayero University ,Kano CSC7307 Computer Communication & Networks Coaxial Cable 22
- 23. Bayero University ,Kano CSC7307 Computer Communication & Networks Coaxial Cable bandwidth of up to 500 MHz much less susceptible to interference than twisted pair high attenuation rate makes it expensive over long distance - more repeaters – especially for digital signaling at higher data rates 23
- 24. Bayero University ,Kano CSC7307 Computer Communication & Networks Coaxial Cable 24
- 25. Bayero University ,Kano CSC7307 Computer Communication & Networks Coaxial Cable 25
- 26. Bayero University ,Kano CSC7307 Computer Communication & Networks Common Applications Television distribution cable TV applications , the television signal that is coming to your house from cable TV uses coaxial cable. Local Area Network 26
- 27. Bayero University ,Kano CSC7307 Computer Communication & Networks 27
- 28. Bayero University ,Kano CSC7307 Computer Communication & Networks Fiber Optic Cable An optical fiber is a thin flexible medium capable of conducting an optical ray. It is made of ultra pure fused silica, glass fiber or even plastic Used by private companies in implementing local data networks require a light source with injection laser diode (ILD) or light-emitting diodes (LED) It has a cylindrical shape and consists of three concentric sections the core, the cladding and the jacket. 28
- 29. Bayero University ,Kano CSC7307 Computer Communication & Networks Fiber Optic Cable 29
- 30. Bayero University ,Kano CSC7307 Computer Communication & Networks Fiber Optic Cable 30
- 31. Bayero University ,Kano CSC7307 Computer Communication & Networks Fiber Optic Cable The core consists of very thin stance of fibers made of glass or plastic. The cladding part is also made of glass or plastic but with a different refractive index Then the jackets surround one or a bundle of cladded fibers. Usually you have 4, 6 , 8 or 16 optical fiber cables as normally it is used in pairs and for data transmission in both directions 31
- 32. Bayero University ,Kano CSC7307 Computer Communication & Networks Fiber Optic Cable 32
- 33. Bayero University ,Kano CSC7307 Computer Communication & Networks How Optical Fiber Works Light travels in a straight line as long as it is moving through a single uniform substance. If a ray of light traveling through one substance suddenly enters another substance (of a different density), the ray changes direction This concept of reflection is used by Fiber-Optic Cable to to guide light through a channel 33
- 34. Bayero University ,Kano CSC7307 Computer Communication & Networks How Optical Fiber Works 34
- 35. Bayero University ,Kano CSC7307 Computer Communication & Networks How Optical Fiber Works As the previous figure shows, if the angle of incidence is less than the critical angle, the ray refracts and moves closer to the surface If the angle of incidence is equal to the critical angle, the light bends along the interface If the angle is greater than the critical angle, the ray reflects (makes a turn) and travels again in the denser substance. The critical angle is a property of the substance, and its value differs from one substance to another. 35
- 36. Bayero University ,Kano CSC7307 Computer Communication & Networks Advantage of Optical Fiber Optical fiber provides higher bandwidth leading to greater capacity (2Gbps over tens of kilometers ) Small in size and very light in weight as it is not a metal Very low attenuation. resistance to corrosive material Immune to electromagnetic interference (very suitable for outdoor applications, outdoor cabling) It has greater repeater spacing compared to either twisted pair or coaxial cable. 36
- 37. Bayero University ,Kano CSC7307 Computer Communication & Networks Disadvantages of Optical Fiber Installation and maintenance (adding additional nodes is difficult) Unidirectional light propagation. Propagation of light is unidirectional. If we need bidirectional communication, two fibers are needed. Cost. The cable and the interfaces are relatively more expensive than those of other guided media. 37
- 38. Bayero University ,Kano CSC7307 Computer Communication & Networks Guided Media Comparison Point-to-Point Characteristics Transmission Rate Bandwidth Repeaters Medium Mbps MHz km . Twisted Pair 100 3.5 2-6 Coaxial 500 500 1-10 Optical Fiber 200000 200000 10-50 38
- 39. Bayero University ,Kano CSC7307 Computer Communication & Networks UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. Unguided signals can travel from the source to destination in several ways: ground propagation, sky propagation, and line-of-sight propagation 39
- 40. Bayero University ,Kano CSC7307 Computer Communication & Networks Wireless Transmission waves Broadly , the electromagnetic spectrum used for wireless communication is divided into three parts Radio waves , Microwaves and Infrared Transmission and reception are achieved by means of antennas 40
- 41. Bayero University ,Kano CSC7307 Computer Communication & Networks
- 42. Bayero University ,Kano CSC7307 Computer Communication & Networks Electromagnetic spectrum for wireless communication 42
- 43. Bayero University ,Kano CSC7307 Computer Communication & Networks Electromagnetic Spectrum
- 44. Bayero University ,Kano CSC7307 Computer Communication & Networks Wireless Transmission Directional (higher frequencies) transmitting antenna puts out focused beam transmitter and receiver must be aligned Omnidirectional (lower frequencies) signal spreads out in all directions can be received by many antennas 44
- 45. Bayero University ,Kano CSC7307 Computer Communication & Networks • 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 Radio Waves
- 46. Bayero University ,Kano CSC7307 Computer Communication & Networks • 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. Microwaves
- 47. Bayero University ,Kano CSC7307 Computer Communication & Networks Unidirectional antennas
- 48. Bayero University ,Kano CSC7307 Computer Communication & Networks Infrared Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation. Wavelength 900 nm Up to 2 Mbps Does not penetrate walls no licensing required
- 49. Bayero University ,Kano CSC7307 Computer Communication & Networks 7.49 Wireless Channels - Interference Are subject to a lot more errors than guided media channels. Interference is one cause for errors, can be circumvented with high SNR. The higher the SNR the less capacity is available for transmission due to the broadcast nature of the channel. Channel also subject to fading and no coverage holes.
- 50. Bayero University ,Kano CSC7307 Computer Communication & Networks Propagation Methods 50
- 51. Bayero University ,Kano CSC7307 Computer Communication & Networks 7.51 Bands
- 52. Bayero University ,Kano CSC7307 Computer Communication & Networks Comparison of Transmission Media