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5.1 | |
Cabling the LAN | |
| 5.1.8 | |
Wireless |
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A wireless network can be created with
much less cabling than other networks. Wireless signals are
electromagnetic waves that travel through the air. Wireless networks
use Radio Frequency (RF), laser, infrared (IR), or
satellite/microwaves to carry signals from one computer to another
without a permanent cable connection. The only permanent cabling can
be to the access points for the network. Workstations within the range
of the wireless network can be moved easily without connecting and
reconnecting network cabling. A common application of wireless data communication is for mobile use. Some examples of mobile use include commuters, airplanes, satellites, remote space probes, space shuttles, and space stations. At the core of wireless communication are devices called transmitters and receivers. The transmitter converts source data to electromagnetic (EM) waves that are passed to the receiver. The receiver then converts these electromagnetic waves back into data for the destination. For two-way communication, each device requires a transmitter and a receiver. Many networking device manufacturers build the transmitter and receiver into a single unit called a transceiver or wireless network card. All devices in wireless LANs (WLANs) must have the appropriate wireless network card installed. The two most common wireless technologies used for networking are IR and RF. IR technology has its weaknesses. Workstations and digital devices must be in the line of sight of the transmitter in order to operate. An infrared-based network suits environments where all the digital devices that require network connectivity are in one room. IR networking technology can be installed quickly, but the data signals can be weakened or obstructed by people walking across the room or by moisture in the air. There are, however, new IR technologies being developed that can work out of sight. Radio Frequency technology allows devices to be in different rooms or even buildings. The limited range of radio signals restricts the use of this kind of network. RF technology can be on single or multiple frequencies. A single radio frequency is subject to outside interference and geographic obstructions. Furthermore, a single frequency is easily monitored by others, which makes the transmissions of data insecure. Spread spectrum avoids the problem of insecure data transmission by using multiple frequencies to increase the immunity to noise and to make it difficult for outsiders to intercept data transmissions. Two approaches currently being used to implement spread spectrum for WLAN transmissions are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). The technical details of how these technologies work are beyond the scope of this course.
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