![]() |
![]() |
![]() |
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
![]() |
![]() |
To access the contents, click the chapter and section titles.
Wireless Networking Handbook
Long-Term Cost SavingsCompanies reorganize, resulting in the movement of people, new floor plans, office partitions, and other renovations. These changes often require re-cabling the network, incurring both labor and material costs. In some cases, the re-cabling costs of organizational changes are substantial, especially with large enterprise networks. A reorganization rate of 15% each year can result in yearly reconfiguration expenses as high as $250,000 for networks having 6,000 interconnected devices. The advantage of wireless networking is again based on the lack of cableyou can move the network connection by simply relocating an employees PC. Wireless Network ConcernsThe benefits of a wireless network are certainly welcomed by companies and organizations. Network managers and engineers should be aware, however, of the following concerns that surround the implementation and use of wireless networking:
Radio Signal InterferenceThe purpose of radio-based networks is to transmit and receive signals efficiently over airwaves. This process, though, makes these systems vulnerable to atmospheric noise and transmissions from other systems. In addition, these wireless networks could interfere with other radio wave equipment. As shown in figure 1.9, interference may be inward or outward. Inward InterferenceMost of us have experienced radio signal interference while talking on a wireless telephone, watching television, or listening to a radio. Someone close by might be communicating with another person via a short-wave radio system, causing harmonic frequencies that you can hear while listening to your favorite radio station. Or, a remote control car can cause static on a wireless phone while you are attempting to have a conversation. These types of interference might also disturb radio-based wireless networks in the form of inward interference.
A radio-based LAN, for example, can experience some inward interference either from the harmonics of transmitting systems or other products using ISM-band frequencies in the local area. Microwave ovens operate in the S band (2.4 GHz) that many wireless LANs transmit and receive. These signals result in delays to the user by either blocking transmissions from stations on the LAN or causing bit errors to occur in data being sent. These types of interference can limit the areas in which you can deploy a wireless network. As an illustration, when deploying a wireless network at a site located in Washington, D.C., along the Potomac River, a company occasionally experienced a great deal of delay from stations located on the side of the building facing the river. The implementation team found, through radio propagation tests, that a military base on the opposite side of the river was periodically transmitting a radio signal. The interfering signal was strong enough for the LAN stations to misinterpret it as data traffic, forcing the stations to wait an inefficient period of time.
Interference with radio-based networks is not as bad as it might seem. The products using the ISM bands incorporate spread spectrum modulation that limits the amount of damage an interfering signal causes. The spread spectrum signal covers a wide amount of bandwidth, and a typical narrow bandwidth interference only affects a small part of the information signal, resulting in few or no errors. Thus, spread spectrum-type products are highly resistant to interference. Narrowband interference with signal-to-interference ratios of less than 10 dB does not usually affect a spread spectrum transmission. Wideband interference, however, can have damaging effects on any type of radio transmission. The primary source of wideband interference is domestic microwave ovens that operate in the 2.4 GHz band. The typical microwave oven operates at 50 pulses per second and sweeps through frequencies between 2400 and 2450 MHz, corrupting the wireless data signal if within 50 feet of the interfering source. Other interference may result from elevator motors, duplicating machines, theft protection equipment, and cordless phones. Outward InterferenceInward interference is only half of the problem. The other half of the issue, outward interference, occurs when a wireless networks signal disrupts other systems, such as adjacent wireless LANs, navigation equipment on aircraft, and so on. This disruption results in the loss of some or all of the systems functionality. Interference is uncommon with ISM band products because they operate on such little power. The transmitting components must be very close and operating in the same bandwidth for either one to experience inward or outward interference. Techniques for Reducing InterferenceWhen dealing with interference, you will want to coordinate the operation of radio-based wireless network products with your companys frequency management organization, if one exists. This will avoid potential interference problems. In fact, the coordination with frequency management officials is mandatory before operating radio-based wireless devices of any kind on a U.S. military base. The military does not follow the same frequency allocations issued by the FCC. The FCC deals with commercial sectors of the U.S., and the military has their own frequency management process. You must obtain special approvals from the government to operate ISM-based products on military bases because they may interfere with some of their systems. The approval process can take several months to complete.
|
![]() |
Products | Contact Us | About Us | Privacy | Ad Info | Home
Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement. |