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To access the contents, click the chapter and section titles.
Wireless Networking Handbook
Bandwidth is the effective part of the frequency spectrum that the signal propagates. For example, the telephone system operates over a bandwidth roughly from 04 KHz. This is enough bandwidth to accommodate most of the frequency components within our voices. Radio wave systems have greater amounts of bandwidth located at much higher frequencies. Data rates and bandwidth are directly proportionalthe higher the data rates, the more bandwidth you will need. The Communications ChannelAll information systems employ a communications channel along which information flows from source to destination. Ethernet networks may utilize twisted-pair or coaxial cable. Wireless networks use air as the medium. At the earths surface, where most wireless networks operate, pure air contains gases such as nitrogen and oxygen. This atmosphere provides an effective medium for the propagation of radio waves and infrared light. Rain, fog, and snow, however, can increase the amount of water molecules in the air and can cause significant attenuation to the propagation of modulated wireless signals. Smog clutters the air, adding attenuation to the communications channel as well. Attenuation is the decrease in the amplitude of the signal, and it limits the operating range of the system. The ways to combat attenuation are to either increase the transmit power of the wireless devices, which in most cases is limited by the FCC, or to incorporate special amplifiers called repeaters that receive attenuated signals, revamp them, and transmit downline to the end station or next repeater. Benefits of Wireless NetworksCompanies can realize the following benefits by implementing wireless networks:
MobilityUser mobility indicates constant physical movement of the person and their network appliance. Many jobs require workers to be mobile, such as inventory clerks, healthcare workers, policemen, emergency care specialists, and so on. Wireline networks require a physical tether between the users workstation and the networks resources, which makes access to these resources impossible while roaming about the building or elsewhere. As an analogy, consider talking on a wired phone having a cord connecting the handset to the telephone base station. You can utilize the phone only within the length of its cord. With a wireless cellular phone, however, you can walk freely within your office, home, or even talk to someone while driving a car. Wireless networking offers mobility to its users much like the wireless phone, providing a constant connection to information on the network. This connection can be extremely useful if you are at a customers site discussing a new product, delivering emergency care to a crash victim, or in a hotel room sending and receiving e-mail. You cannot become mobile unless you eliminate the wire through the use of wireless networking. Installation in Difficult-to-Wire AreasThe implementation of wireless networks offers many tangible cost savings when performing installations in difficult-to-wire areas. If rivers, freeways, or other obstacles separate buildings you want to connect (see fig. 1.8), a wireless MAN solution may be much more economical than installing physical cable or leasing communications circuits such as T1 service or 56 Kbps lines. Some organizations spend hundreds, thousands, or even millions of dollars to install physical links with nearby facilities. If you are facing this type of installation, consider wireless networking as an alternative. The deployment of wireless networking in these situations costs thousands of dollars, but will result in a definite cost savings in the long run.
The asbestos found in older facilities is another problem that many organizations encounter. The inhalation of asbestos particles is extremely hazardous to your health; therefore, you must take great care when installing network cabling within these areas. When taking necessary precautions, the resulting cost of cable installations in these facilities can be prohibitive. Some organizations, for example, remove the asbestos, making it safe to install cabling. This process is very expensive because you must protect the buildings occupants from breathing the asbestos particles agitated during removal. The cost of removing asbestos covering just a few flights of stairs can be tens of thousands of dollars. Obviously, the advantage of wireless networking in asbestos-contaminated buildings is that you can avoid the asbestos removal process, resulting in tremendous cost savings. In some cases, it might be impossible to install cabling. Some municipalities, for example, may restrict you from permanently modifying older facilities with historical value. This could limit the drilling of holes in walls during the installation of LAN cabling and network outlets. In this situation, a wireless LAN might be the only solution. Right-of-way restrictions within cities and counties may also block the digging of trenches in the ground to lay optical fiber for the interconnection of networked sites. Here, a wireless MAN or WAN might be the only alternative. Reduced Installation TimeThe installation of cabling is often a time-consuming activity. For LANs, installers must pull twisted-pair wires above the ceiling and drop cables through walls to network outlets that they must affix to the wall. These tasks can take days or weeks, depending on the size of the installation. The installation of optical fiber between buildings within the same geographical area consists of digging trenches to lay the fiber or pulling the fiber through an existing conduit. You might need weeks or possibly months to receive right-of-way approvals and dig through ground and asphalt. The deployment of wireless LANs, MANs, or WANs greatly reduces the need for cable installation, making the network available for use much sooner. Thus, many countries lacking a network infrastructure have turned to wireless networking as a method of providing connectivity among computers without the expense and time associated with installing physical media. Increased ReliabilityA problem inherent to wired networks is the downtime due to cable faults. Moisture erodes metallic conductors. These imperfect cable splices can cause signal reflections that result in unexplainable errors. The accidental cutting of cables can also bring a network down quickly. Water intrusion can also damage communications lines during storms. These problems interfere with the users ability to utilize network resources, causing havoc for network managers. The advantage of wireless networking, then, is experiencing fewer problems because less cable is used.
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