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Chapter 7 Transmission Media

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Presentation on theme: "Chapter 7 Transmission Media"— Presentation transcript:

1 Chapter 7 Transmission Media
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Located below the physical layer Controlled by the physical layer
Figure Transmission medium and physical layer Transmission medium(channel): the physical path between the transmitter and the receiver. Located below the physical layer Controlled by the physical layer

3 Figure 7.2 Classes of transmission media

4 7.1 Guided Media Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable

5 A wire pair acts as a single communication link
Figure Twisted-pair cable A twisted pair consists of: two insulated copper wires in a regular spiral pattern A wire pair acts as a single communication link Twisted to reduce electrical interference from similar pairs close by (more twists means better quality) Used in: Telephone network Between house and local exchange (subscriber loop) LAN

6 Twist length of 7.5 cm to 10 cm Twist length 0.6 cm to 0.85 cm


8 Figure UTP and STP UTP: Unshielded Twisted Pair STP: Shielded Twisted Pair

9 Unshielded Twisted Pair (UTP)
Used for telephone wire Cheapest type of cable Easiest type to be installed Suffers from external Electromagnetic (EM) interference Shielded Twisted Pair (STP) Metal braid or covering that reduces interference More expensive Harder to handle (thick, heavy)

10 Table 7.1 Categories of unshielded twisted-pair cables

11 Figure UTP connector RJ=Registered Jack

12 Twisted pairs

13 The RJ-45 Connector TD+ : Transmit Data Positive value
White/Orange Orange White/Green Green Brown 2 3 The RJ-45 Connector 1 8 TD+ : Transmit Data Positive value TD- : Transmit Data Negative value RD+ : Receive Data Positive value RD- : Receive Data Negative value

14 TD+ : Transmit Data Positive value TD- : Transmit Data Negative value
RD+ : Receive Data Positive value RD- : Receive Data Negative value White/Orange Orange White/Green Green Brown

15 Ethernet Cabling Crossover Cabling Straight-Through Cabling PC to PC
Hub to Hub Switch to Switch Hub to Switch Router to PC PC to Switch/Hub Router to Switch/Hub

16 Switch Router Hub

17 Coaxial Cable Connectors used in bus technology BNC BNC-T Terminator
insulating conductor Copper wires (braid or foil) External coat Connectors BNC BNC-T Terminator

18 Table 7.2 Categories of coaxial cables Category Use RG-59 Cable TV
Thin Ethernet 10base2 RG-11 Thick Ethernet 10base5 Radio Government


20 Optical Fiber consists of three concentric sections glass or plastic
cover plastic jacket Fiber core and clading Core: consists of one or more very thin strands or fibers made of glass or plastic Each fiber is surrounded by its own cladding, a glass or plastic coating that has optical properties different from the core Jacket: a plastic or other material acts as a layer to protect against moisture, crushing, and other environmental dangers.

21 Fiber Optic Cable A fiber optic cable consists of two strands. Each strand has a glass or plastic core surrounded by more glass called cladding. The center strand provides the wave path while the cladding is composed of reflective glass that refracts light back to the core. Each strand is covered in a jacket composed of a group of Kevlar fibers for strength, and a reinforcing layer of plastic.. Since, each glass strand only passes signals in one direction, a cable has two strands in separate jackets. Special connectors make up an optically pure connection to the glass fiber and provide a window for laser transmitters and optical receivers. Fiber optic cable is not impacted by outside electric currents because the signals it carries are pulses of light conducted over threads of glass. Because they are free from interference and the light pulses travel for miles without losing appreciable strength, fiber optic cables can carry data at high signaling speeds over long distances. Speeds easily exceed 100 Mbps and distances range approximately 2 Km. Two Types of Fiber Cable follow: Single-Allows only one mode of light to propagate through the fiber, capable of higher bandwidth and greater distances than multimode. Often used for campus backbones. Uses lasers as the light generating method. About the diameter of human hair (8 microns thick). Multi-mode-Allows multiple modes of light to propagate through the fiber. Often use for workgroup applications. Uses light-emitting diodes (LEDs) as light generating device. Fiber optic cables are far more costly than UTP.

22 Optical Fiber

23 Optical Fiber - Advantages
Greater capacity Data rates of hundreds of Gbps Smaller size & weight Lower attenuation (signal loss) Greater repeater spacing 10s of km at least No crosstalk (no light leaking) Electromagnetic isolation highly secure (no light leaking)

24 Optical Fiber - Disadvantages
Not easy to install and maintain Unidirectional, two fibers are needed for bidirectional Cost: more expensive interfaces than electrical interfaces used with other types (twisted, coaxial)


26 Optical Fiber - Applications
Long-distance trunks (1500 km) Subscriber loops (to replace twisted pair) LANs (100 Mbps – 10 Gbps)

27 7.2 Unguided Media: Wireless
Radio Waves Microwaves Infrared

28 Figure 7.19 Wireless transmission waves
Unguided media: signals are transmitted through air and are available to everyone who has a device that can receive them

29 The Electromagnetic Spectrum

30 Figure 7.17 Electromagnetic spectrum for wireless communication

31 Table 7.4 Bands

32 Figure 7.18 Propagation methods

33 Radio waves 30MHz to 1GHz Omnidirectional (signal propagates in all directions) Easily interfere with other signals sent at the same frequency range Can penetrate walls and can be received in the building Does not require dish-shaped antennas Broadcast radio (AM,FM) ,TV, cordless phone, Paging, cellular phones

34 Note Radio waves are used for multicast communications, such as radio and television, and paging systems.

35 Microwaves 2GHz to 300GHz Highly directional (line-of-sight propagation = straight lines) Requires dish-shaped antennas Point to point (sending and receiving antennas need to be aligned) Very high frequency microwaves, usually, cannot penetrate walls (disadv. if receivers are inside buildings) Used in long distance telephone communications Used for short point-to-point transmission between buildings to connect their LANs Used in Wireless networks, satellite communication

36 Note Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

37 Infrared 300GHz to 400THz Have a very large bandwidth that is not yet completely utilized Local- short distance communication Line-of-sight propagation (directional) Used in local point-to-point Transmission or Multipoint within a very limited area (single room) Used in Remote control, IrDA (Infrared Data Association) port (wireless keyboard, mouse) Cannot be used under the sun because of the interference with the sun infrared rays IrDA operates at 75kbps up to 8 meters, and 1.15Mbps – 4Mbps over a distance of 1 meter

38 Note Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

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