transmission medias

8/3/2019 Transmission Medias

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7.1


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Transmission medium and physical layer


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Classes of transmission media


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GUIDED MEDIAGUIDED MEDIA

GuidedGuided media,media, whichwhich areare thosethose thatthat provideprovide aa conduitconduit

fromfrom oneone devicedevice toto another,another, includeinclude twistedtwisted--pairpair cable,cable,

coaxialcoaxial cable,cable, andand fiberfiber--opticoptic cablecable..

Twisted-Pair Cable

Coaxial Cable

Fiber-Optic Cable

Topics discussed in this section:Topics discussed in this section:


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7.5

Figure 7.3 Twisted-pair cable


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7.6

Figure 7.4 UTP and STP cables


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Categories of unshielded twisted-pair cables


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UTP connector


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Coaxial cable


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7.10

Table 7.2 Categories of coaxial cables


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7.11

Figure 7.8 BNCconnectors


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7.12


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Optical fiber


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Propagation modes


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7.15


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Modes


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Fiber types


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Fiber construction


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Fiber-optic cable connectors


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7.20


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7.21


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Optical fiber performance


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UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

UnguidedUnguided mediamedia transporttransport electromagneticelectromagnetic waveswaves

withoutwithout usingusing aa physical physical conductorconductor. . ThisThis typetype ofof

communicationcommunication isis oftenoften referredreferred toto asas wirelesswireless

communicationcommunication..

Radio Waves

Microwaves

Infrared

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Electromagnetic spectrum for wireless communication


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Propagation methods


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Ground propagation. In ground propagation,radio waves travel through the lowest portion ofthe atmosphere, hugging the earth. These low-

frequency signals emanate in all directions fromthe transmitting antenna and follow the curvatureof the planet. The distance depends on the powerin the signal.

In Sky propagation, higher-frequency radio

waves radiate upward into the ionosphere wherethey are reflected back to earth. This type oftransmission allows for greater distances withlower power output.

In Line-of-Sight Propagation, very highfrequency signals are transmitted in straight lines

directly from antenna to antenna.


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Bands


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Wireless transmission waves


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Radio waves are used for multicastcommunications, such as radio and

television, and paging systems. They

can penetrate through walls.

Highly regulated. Use omni directional

antennas

Note


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Omnidirectional antenna


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Microwaves are used for unicast

communication such as cellulartelephones, satellite networks,

and wireless LANs.

Higher frequency ranges cannotpenetrate walls.

Use directional antennas - point to point

line of sight communications.

Note


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Figure 7.21 Unidirectional antennas


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Infrared signals can be used for short-

range communication in a closed area

using line-of-sight propagation.

Note


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Wireless Channels

Are subject to a lot more errors than guidedmedia channels.

Interference is one cause for errors, can becircumvented with high SNR.

The higher the SNR the less capacity isavailable for transmission due to the

broadcast nature of the channel. Channel also subject to fading and no

coverage holes.

transmission medias

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