Choosing Locations for Access Points
| Just as you need to test new network configurations or PC configurations in a laboratory before rolling them out for production usage, you need to evaluate the placement of APs should you decide to get into wireless networking. Wi-Fi provides for roaming capabilities, but it also enables you to restrict users to selected APs if you choose to do so. First, decide how you want to use wireless networking and which users it can be used by in a productive manner. Next, decide how many APs you need and where to place them. You'll have to do some experimentation. Read the vendor's documentation to get the basics of the coverage area that the product is capable of, keeping in mind that this is only a general figure. For example, you'll find that most APs are capable of covering larger distances outside, rather than inside, because there are fewer structural components, such as bricks or steel beams, that can block the signal. You should take a vendor's specifications about its particular product with a grain of salt. Your mileage can vary. If you use wireless networking inside and want to cover the entire building, you'll have to test to see exactly how far the coverage is for each AP. Also note that several factors can influence the performance you'll get no matter where you place the AP. For example, each AP is capable of supporting only a limited number of users before the available bandwidth begins to become saturated. Although 802.11g hardware is the overall favorite in SOHO and public-access networks, the higher frequency used by 802.11a enables it to support more users than with 802.11g. For maximum speed and flexibility in your business network, using dual-mode 802.11a/802.11g wireless APs and adapters is recommended. Another thing to consider is source of interference, such as microwave ovens and other wireless devices. If you employ Bluetooth devices, you need to be careful because Bluetooth can interfere with Wi-Fi 2.4GHz (802.11b and 802.11g) devices when used at distances of 2cm or less or distances greater than 10cm (for example, a user with a Bluetooth keyboard/mouse or a Bluetooth wireless headset using a computer with an 802.11g wireless network adapter might have problems). Although Bluetooth has been improved with technology such as adaptive frequency hopping (first introduced in Bluetooth version 1.2) to try to minimize interference, the use of Bluetooth in close proximity to 2.4GHz Wi-Fi devices can virtually shut down the 2.4GHz Wi-Fi devices. If you plan to use Wi-Fi and Bluetooth devices in your organization, consider using 802.11a or dual-band 802.11a/802.11g wireless APs and adapters. 802.11a does not use the same frequency as 802.11g or Bluetooth. Note Richard Quinnell provides an excellent summary of the current challenges facing Wi-Fi 2.4GHz and Bluetooth operations in close proximity in his August 2005 article "WiFi and Bluetooth Fight for Bandwidth." Find it online at www.edn.com/article/CA629312.html. Another popular SOHO and office device is the 2.4GHz cordless telephone. These telephones operate in the same band as 2.4GHz wireless networks and can cause problems when used in the vicinity of wireless networking devices. Consider upgrading to 5.8GHz wireless phones if you use 2.4GHz Wi-Fi wireless network hardware. If you also use 5GHz (802.11a) wireless networking, don't worry: 5.8GHz phones do not cause significant interference with 5GHz Wi-Fi (802.11a) wireless networks. Some types of wireless mouse devices and keyboards also present a risk of conflict. All Bluetooth-based devices, including wireless mouse devices and keyboards, use the 2.4GHz band, as do many non-Bluetooth implementations from various vendors. To help prevent conflicts, many of these devices support multiple channels. Use the contact information in Table 53.1 to determine if a particular 2.4GHz input device might conflict with your existing 2.4GHz devices.
Tip If a wireless mouse or keyboard has a maximum range of six feet or less, it uses 27MHz technology. A wireless mouse or keyboard with a maximum range of 25 feet or further uses 2.4GHz technology. Check the device's specifications to determine if the device uses Bluetooth or a proprietary implementation. Table 53.1 lists many popular non-Bluetooth input devices that use the 2.4GHz RF band. And keep that microwave oven in the break room well shielded! You can purchase an inexpensive device at most consumer discount stores that can measure the amount of microwave radiation that's leaking from a microwave oven. You might find that simply replacing an old microwave oven with a newer model cures any interference problems. And because most work places don't need a top-of-the-line microwave that can zap a baked potato in just a few minutes, go with a low-end model that uses less power. |
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