Physical layer-Transmission media

Transmission media are actually located below the physical layer and are directly controlled by the physical layer.

A transmission medium can be broadly defined as anything that can carry information from a source to a destination

The transmission medium is usually free space, metallic cable, or fiber-optic cable.

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Transmission medium and physical layer

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Classes of transmission media

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Twisted-pair cable

Guided media, which are those that provide a conduit from one Guided media, which are those that provide a conduit from one device to another, include twisteddevice to another, include twisted--pair cable, coaxial cable, and pair cable, coaxial cable, and fiberfiber--optic cable.optic cable.

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In a shielded twisted pair (STP), the wires are enclosed in a shield that functions as a grounding mechanism. This is done to provide greater protection from electromagnetic interference and radio frequency interference; however, STP cable is more expensive and difficult to install, compared with UTP.

Unshielded twisted pair (UTP) is a type of copper cabling used in telephone wiring and local area networks (LANs). There are 8 types of UTP cables --identified with the prefix CAT, as in category -- each supporting a different amount of bandwidth.

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UTP connector

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UTP performance

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Coaxial cable

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Figure 7.9 Coaxial cable performance

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Optical fiber cable

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Figure 7.14 Fiber construction

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UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

Unguided media transport electromagnetic waves without using a Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred physical conductor. This type of communication is often referred to as wireless communicationto as wireless communication

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Wireless transmission waves

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Electromagnetic spectrum for wireless communication

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Propagation methods

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Bands

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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

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 short-range communication

in a closed area using line-of-sight propagation

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Wireless Channels

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.

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