Wireless LAN technology is nothing new, but it is only now beginning to catch on, especially on college campuses where laptops are widely used. Carnegie Mellon University has installed more than 400 access points (transceivers, a type of antenna) around the campus, including in its cafeterias, and it has sold wireless LAN cards to 1,500 students. Wake Forest University, which issues each incoming freshman a notebook PC, has added a wireless Ethernet card to each PC. Wireless LANs are less common in schools and public libraries because a much smaller percentage of their patrons carry laptops, but the few installations that exist have been well-received.
Wireless LAN technology was held back for years by the instability of many of the manufacturers, a lack of standards, and poor interoperability among components from different vendors.
With Cisco Systems' recent acquisition of Aironet, all the major providers of networks— Cisco, Enterasys Networks, Lucent Technologies, and Nortel Networks—have wireless offerings. These companies have staying power that assures customers of ongoing support.
The companies above are committed to the IEEE 802.llb standard for wireless LANs. Widespread adoption of the 802.llb standard is the key to interoperability among products from different vendors. Not all 802.llb implementations offer full interoperability, so look for WECA (Wireless Ethernet Compatibility Alliance) certification. That certification means you can augment or replace components using competitive bidding, rather than purchasmg everything from a single vendor. As a result, prices have come down as much as 75% in the past year. An access point (transceiver) now costs $1,000 to $2,000; the wireless PC card now costs about $175.
Although enthusiasts proclaim the appearance of wireless LANs presages the disappearance of wired LANs, others suggest wireless continues to have significant weaknesses.
Not all available products conform to the 802.llb standard. The Federal Communication Commission (FCC) has approved a competing standard in response to requests from manufacturers of HomeRF equipment. The standard, which is supported by RadioShack Corp., Motorola, and some PC manufacturers, provides for frequency-hopping LAN throughput—which, as the name implies, hops among 15 different channels in the 2.4 0Hz band. The 802.llb standard calls for direct sequencing, an approach that evenly spreads the signals across all the channels in the band.
Another competing standard is called Bluetooth. It was developed to provide wireless connections between laptops and printers, but some vendors use it for small LANs. Some proprietary products are still on the market, too.
Conformity to any of the standards above doesn't mean you'll realize the 11 Mbps throughput specified in the standard. The actual throughput is more likely 4 to 6 Mbps. Wired networks perform more closely to their standards—standards that provide for throughput of up to 10 bps or up to 250 times that of wireless. That performance means wired LANs continue to be necessary for the backbone of a LAN because the aggregate bandwidth required within most libraries exceeds 10 Mbps, and in some it exceeds 100 Mbps. Wireless is best used for the last few yards to the desktop, rather than throughout a building.
Dead space is a common problem with wireless LANs. Unless the transceivers (the hub-like transmitter/receivers that connect to the physically cabled network via standard Ethernet cable, and then to the server or other device) are properly placed, some areas have no service. Testing the installation for dead space and relocating or adding transceivers as needed is key.
Interference is another, and growing, problem. Wireless LANs share the 2.4 GHz frequency band not only with other wireless LANs (frequency-hopping LANs, especially, can interfere with direct sequencing), but they also can interfere with other devices, such as cordless telephones, microwave ovens, and short-range Bluetooth devices. Dense urban areas often suffer from serious degradation of performance. The FCC is getting complaints about interference and members of an advisory group told the FCC someday 2.4 GHz will only work outside urban areas. The FCC has been urged to allocate additional frequencies for wireless LANs. The most likely additional frequency is 5 GHz. Such a move would require replacement of wireless equipment in areas where the 2.4 0Hz frequency is saturated.
Libraries considering a wireless LAN should consult the ratings of 11 products published by Network Computing (July 10, 2000, pp. 69-91). The information is also available at www.networkcomputing.com. The three highest rated products, all A-, are available from Cisco Systems, Enterasys Networks, and Lucent Technologies.
Relying entirely on wireless is not a good idea. Wireless is best used in parts of a building that are difficult and costly to wire or for an area in which you want to provide wireless access from laptops. Although the 802-11 standard is the one supported by all major networking companies, keep in mind that laptops used within the library also have to have an 802.llb wireless LAN card. Patrons who bring a laptop with a HomeRF or Bluetooth card won't be able to access the network.
Before deploying a wireless LAN, conduct a site survey to determine existing sources of interference and work to alleviate as many of them as possible. After making the initial installation, undertake testing to determine dead spots and make adjustments as needed. The surveying and testing requires considerable expertise, so a library should budget for a consultant who specializes in wireless LANs.
