An update on the .11b, .11a, .11g, .11i, and .1x standards and the devices that support them
Once you've experienced the freedom of wireless networking, you won't want to revert to a wired world. Access to server-based information makes meetings more productive, and the ability to access email from anywhere on campus speeds the decision-making process. For companies that frequently need to reorganize workgroups or that are about to install a network in a temporary space, wireless LANs (WLANs) can save time and money.
Two 802.11 Standards
Wireless networking isn't a new concept—WLAN standards such as HomeRF, 802.11, and OpenAir have been around for some time. But slow speeds and high prices made the technology impractical for enterprise use until the IEEE approved the 11Mbps 802.11b wireless networking standard in 1999. Since then, interest in 802.11b wireless products has surged and prices for wireless NICs have dropped. Still, street prices for wireless NICs run between $100 and $200, which is at least three times the cost of wired NICs, and access points (i.e., base stations that connect to your wired network) cost anywhere from $300 to $800. A long list of vendors, including Agere Systems, Intel, Intermec Technologies, Cisco Systems, Avaya, D-Link Systems, 3Com, Proxim, and Symbol Technologies, offer 802.11b hardware.
The IEEE also introduced a 54Mbps standard known as 802.11a in 1999, but because of this standard's complexity, 802.11a products were just being introduced at press time by a few vendors, including Intel, Proxim, and Intermec, with others sure to follow. In addition to being speedier than 802.11b, 802.11a uses a fairly large slice of the radio spectrum at 5GHz. 802.11a doesn't share its spectrum slice with other services, so 802.11a networks should operate with a minimum of interference. The 802.11b standard uses a narrow slice of the radio spectrum at 2.4GHz—an allocation it shares with cordless phones and Bluetooth wireless devices. You might have heard that microwave ovens can leak radiation into this part of the radio spectrum, but vendors report that microwave leakage hasn't been a major disruption. However, as WLANs, 2.4GHz cordless phones, and Bluetooth devices increase in popularity, interference in this limited spectrum space could reduce the performance of WLANs. Before you invest in wireless networking, you should test products in your environment to locate and alleviate interference sources.
Although 802.11a and 802.11b are marketed as 54Mbps and 11Mbps standards, respectively, the high overhead of their wireless protocols reduces their effective throughput to roughly 27Mbps and 6Mbps, respectively, under the best conditions. By contrast, wired Ethernet provides an effective throughput of about 7.5Mbps.
If you're planning to invest in WLAN technology, the faster 802.11a might seem like the obvious choice, but incompatibility with the more established 802.11b standard, potential range limitations, and higher prices might dim its attractiveness. In typical indoor office conditions, an 802.11b wireless-LANequipped PC might be able to communicate with an access point that's 300 feet away; the raw data rate might start at 11Mbps, then drop to about 5.5Mbps beyond 100 feet, then to about 2Mbps, and finally to 1Mbps at the outer coverage limit. Preliminary data from 802.11a vendors implies a similar range (with raw data rates from 54Mbps to 6Mbps, depending on signal quality), but the laws of physics suggest that all else being equal, doubling the operating frequency could cut range by 50 percent or more, depending on the number and type of obstructions. If the range of 802.11a products does turn out to be appreciably lower than that of 802.11b products, you might need to purchase more access points to cover the same physical area.
If you've already invested in 802.11b WLAN technology (or expect frequent visitors that use 802.11b wireless NICs), adding 802.11a WLAN products to your network presents a problem because the two designs use different frequency allocations. Of the 802.11a wireless NICs introduced by press time, none offer dual-mode capability that would let them work with 802.11b access points. However, several access points typically support both the 802.11b and 802.11a standards. Agere Systems' ORiNOCO AS-2000 Access Server ($1495 list) and ORiNOCO AP-2000 Access Point ($1295 list) can use an 802.11b radio and the company's forthcoming 802.11a radio simultaneously. (Each radio in an access point operates on a designated wireless channel and can support as many as 50 or 60 NICs.) Intel offers a similar solution in a version of its PRO/Wireless 5000 LAN Access Point that supports an 802.11a radio and an 802.11b radio (pricing wasn't available at press time). Intermec's MobileLAN access 2106 802.11a-compliant access point supports only one radio but features a built-in Remote Authentication Dial-In User Service (RADIUS) server, costs roughly the same as its 802.11b counterpart (the MobileLAN access 2102, $895 list), and is compatible with the vendor's existing MobileLAN family of options and management software.
If you really need the additional bandwidth that 802.11a WLAN solutions offer but want products that can easily interoperate with your existing 802.11b access points, you might want to wait a bit longer before making a buying decision. At press time, the IEEE 802.11 Task Group G was considering a proposal that would introduce a new 54Mbps 802.11g wireless standard that uses 802.11a's modulation technique and 802.11b's 2.4GHz frequency allocation. Products based on the 802.11g standard would be compatible with existing 802.11b access points. However, even if the 802.11g proposal is ratified, products might not appear before mid- to late year and the limited 2.4GHz spectrum might be a problem, particularly in high-rise buildings in which tenants on adjacent floors are using 802.11b or 802.11g equipment.
Don't assume that all products within a particular standard are compatible with one another. To ensure interoperability, WLAN vendors offering 802.11b-compliant products formed the Wireless Ethernet Compatibility Alliance. WECA tests products for basic interoperability and lets those that pass its tests carry the Wi-Fi (the 802.11b wireless standard) logo on their packaging and advertising. You can view the WECA test plan at http://www.wi-fi.com/ downloads/test_matrix.pdf. Products that are Wi-Fi certified should interoperate regardless of who built them, but you should still conduct tests to ensure that all aspects of the products you're considering interoperate with NICs and access points that you already own.
WECA says it will begin similar interoperability testing of 802.11a products as more offerings that use chipsets from more than one manufacturer become available. If and when the IEEE 802.11 Task Group G ratifies a 2.4GHz 54Mbps WLAN standard and a sufficient number of 802.11g-compliant products reach the market, I expect WECA to serve a similar interoperability-certification role for these products.