Transmission Media r735n

Transmission Media * Transmission media lie below the physical layer. * A guided medium provides a physical conduit from one device to another. * Twisted-pair cable, coaxial cable, and optical fiber are the most popular types of guided media. * Twisted-pair cable consists of two insulated copper wires twisted together. Twisting allows each wire to have approximately the same noise environment. * Twisted-pair cable is used in telephone lines for voice and data communications. * Coaxial cable has the following layers (starting from the center): a metallic rod-shaped inner conductor, an insulator covering the rod, a metallic outer conductor (shield), an insulator covering the shield, and a plastic cover. * Coaxial cable can carry signals of higher frequency ranges than twisted-pair cable. * Coaxial cable is used in cable TV networks and traditional Ethernet LANs. * Fiber-optic cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket. * Fiber-optic cables carry data signals in the form of light. The signal is propagated along the inner core by reflection. * Fiber-optic transmission is becoming increasingly popular due to its noise resistance, low attenuation, and high-bandwith capabilities. * Signal propagation in optical fibers can be multimode (multiple beams from a light source) or single-mode (essentially one beam from a light source). * In multimode step-index propagation, the core density is constant and the light beam changes direction suddenly at the interface between the core and the cladding. * In multimode graded-index propagation, the core density decreases with distance from the center. This causes a curving of the light beams. * Fiber-optic cable is used in backbone networks, cable TV networks, and Fast Ethernet networks. * Unguided media (usually air) transport electromagnetic waves without the use of a physical conductor. * Wireless data is transmitted through ground propagation, sky propagation, and line-of-sight propagation. * Wireless data can be classifed as radio waves, microwaves, or infrared waves. * Radio waves are omnidirectional. The radio wave band is under government regulation. * Microwaves are unidirectional; propagation is line of sight. Microwaves are used for cellular phone, satellite, and wireless LAN communications. * The parabolic dish antenna and the horn antenna are used for transmission and reception of microwaves. * Infrared waves are used for short-range communications such as those between a PC and a peripheral device. Please answer all questions.

1

Transmission media are usually categorized as _______. A) B) C) D)

2

fixed or unfixed guided or unguided determinate or indeterminate metallic or nonmetallic

Transmission media lie below the _______ layer.

A) B) C) D)

physical network transport application

3

_______ cable consists of an inner copper core and a second conducting outer sheath. Twisted-pair A) Coaxial B) Fiber-optic C) Shielded twisted-pair D)

4

In fiber optics, the signal is _______ waves. A) B) C) D)

5

B) C) D)

infrared very low-frequency

cellular telephone system local telephone system satellite communications radio broadcasting

Which of the following is not a guided medium? A) B) C) D)

7

radio

Which of the following primarily uses guided media? A)

6

light

twisted-pair cable coaxial cable fiber-optic cable atmosphere

What is the major factor that makes coaxial cable less susceptible to noise than twisted-pair cable? inner conductor A)

B) C) D)

8

outer conductor insulating material

In an optical fiber, the inner core is _______ the cladding. A) B) C) D)

9

diameter of cable

denser than less dense than the same density as another name for

The inner core of an optical fiber is _______ in composition. A) B) C) D)

glass or plastic copper bimetallic liquid

10

When a beam of light travels through media of two different densities, if the angle of incidence is greater than the critical angle, _______ occurs. reflection A) refraction B) incidence C) criticism D)

11

When the angle of incidence is _______ the critical angle, the light beam bends along the interface. more than A) less than B) equal to C) none of the above D)

12

Signals with a frequency below 2 MHz use _______ propagation. A) B)

ground sky

C) D)

13

B) C) D)

B) C) D)

B) C) D)

line-of-sight none of the above

ground sky line-of-sight none of the above

omnidirectional bidirectional unidirectional horn

A(n) _____ medium provides a physical conduit from one device to another. A) B) C) D)

17

sky

A parabolic dish antenna is a(n) _______ antenna. A)

16

ground

Signals with a frequency above 30 MHz use _______propagation. A)

15

none of the above

Signals with a frequency between 2 MHz and 30 MHz use ______ propagation. A)

14

line-of-sight

guided unguided either (a) or (b) none of the above

________ cable consists of two insulated copper wires twisted together. A) B) C) D)

Coaxial Fiber-optic Twisted-pair none of the above

18

_______ cable is used for voice and data communications. A) B) C) D)

19

Fiber-optic Twisted-pair none of the above

__________ consists of a central conductor and a shield. A) B) C) D)

20

Coaxial

Coaxial Fiber-optic Twisted-pair none of the above

_____ cable can carry signals of higher frequency ranges than _____ cable. A) B) C) D)

Twisted-pair; fiber-optic Coaxial; fiber-optic Coaxial; twisted-pair none of the above

21

______ cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket. Coaxial A) Fiber-optic B) Twisted-pair C) none of the above D)

22

______ cables carry data signals in the form of light. A) B) C) D)

23

Coaxial Fiber-optic Twisted-pair none of the above

In a fiber-optic cable, the signal is propagated along the inner core by _______.

A) B) C) D)

reflection refraction modulation none of the above

24

_________ media transport electromagnetic waves without the use of a physical conductor. Guided A) Unguided B) Either (a) or (b) C) None of the above D)

25

Radio waves are _________. A) B) C) D)

26

B) C) D)

bidirectional none of the above

omnidirectional unidirectional bidirectional none of the above

_______ are used for cellular phone, satellite, and wireless LAN communications. A) B) C) D)

28

unidirectional

Microwaves are _________. A)

27

omnidirectional

Radio waves Microwaves Infrared waves none of the above

________ are used for short-range communications such as those between a PC and a peripheral device. Radio waves A)

B) C) D)

Microwaves Infrared waves none of the above