WIRELESS LANs
By Richard W. Boss
Interest in wireless local area networks (wireless LANs or WLANs) has been growing exponentially, including in libraries. More were installed in the last quarter of 2001 than in the two previous quarters combined. The acceptance of the technology appears to be attributable to the fact that standards are now in place that address many of the shortcomings of earlier wireless technology. This technology is particularly appealing in buildings where additional wiring will damage new and historic finishes. It also provides an infrastructure to allow public users to connect their own wireless-equipped laptop PCs to the Library's network.
Definition
A wireless LAN makes it possible for a desktop or notebook PC, or for a PDA, to access a local area network without being physically connected to it. It is rare for a wireless LAN to be deployed throughout an entire building; typically it is installed in an area that is difficult to wire or where a large number of mobile users with notebook computers or PDAs may be working.
The typical wireless LAN involves the installation of access points on the interior walls and/or ceilings of a building. Each access point, typically the size of a book, houses a transmitter, a receiver, an antenna, and a piece of equipment that acts as a bridge to an organization's wire- based network. A single access point can serve a number of users, but as more people connect, each person gets a smaller share of the bandwidth--which translates into a slower network connection. A user who has a compatible communications card or "wireless adapter" in his or her desktop or notebook PC can be anywhere within several hundred feet from an access point and remain connected to the network because the wireless radio signal carries through most walls, floors, and ceilings.
The major vendors of wireless LAN components are Avaya (formerly Lucent) Cisco, Intersil, Nokia, Symbol Technologies, and 3Com. All maintain Web sites.
Standards
Most of the recently installed wireless LANs are based on the IEEE (Institute of Electrical and Electronics Engineers) 802.11b standard of 1999, a standard that specifies use of the 2.4 GHz band at 11 Mbps. The 802.11b standard replaced the now outdated 802.11 standard. While a modest commercial success at $1 billion per year, products conforming to the IEEE 802.11b standard have been subject to interference from other applications using the 2.4 GHz band, and performance well below 11 Mbps. Among the products that interfere with 802.11b products are cordless telephones, cellular radios, wireless audio speakers, microwave ovens, wireless karaoke machines, and many remote controls--all common, especially in cities. In tests conducted in 2000 by Schneider National Labs in Green Bay, WI for Network Computing, a major networking journal, most wireless LANs based on the 802.11b standard performed at around 3.2 Mbps. Only one product topped out at more than 4.0 Mbps.
Interoperability among products was a problem with the early versions of products based on the 802.11b standard. It was two years after the standard was adopted that 3Com, Aironet, Intersil, Lucent (now Avaya), Nokia, and Symbol Technologies formed a group called the Wireless Ethernet Compatibility Alliance (WECA). The group's aim is to give customers cast- iron guarantees that products from the participating vendors will work together perfectly.
Security has also been an issue. Because radio frequencies are shared among users of the network, any information sent or received can be intercepted. Radio frequencies frequently "leak" out of buildings onto adjacent streets and parking lots, therefore, making it possible for those not affiliated with an organization to "listen in." However, there is now a solution if security is a concern: encryption can be used and access can be limited to network cards that have been registered.
New products based on the 802.11a standard, which was adopted in November 2001, operate in the 5 Ghz band at up to 54 Mbps. The use of the 5 Ghz band dramatically reduces interference because the band is little used by other applications. Preliminary tests of prototype products in late 2001 suggest that actual bandwidth will exceed 30 Mbps. Cahners In-Stat Group, a market research firm, has estimated that the WLAN market will grow to $4.6 billion by 2005 as the result of the new standard's adoption.
While 802.11b products from WECA members are now interoperable with other products which conform to the same standard, they are not compatible with products which conform to the 802.11a standard, therefore, organizations using equipment based on the older standard will either continue using that standard or face significant replacement costs. Products based on the 802.11b standard continue to be produced, and prices have come down 40 percent in the past few months, therefore, organizations that are satisfied with 802.11b products may continue to invest in them.
There is yet another option. The IEEE has recently adopted IEEE 802.11g, a standard that uses the 2.4 Ghz band, but bumps bandwidth up to 54 Mbps. It is compatible with 802.11b; therefore, users will not have to replace their wireless adapters. Its main drawback is that, like 802.11b, it does not address the problem of interference. Another drawback is that 802.11g products may not become available until 2003--more than a year after the availability of 802.11a. Market observers expect 802.11g to appeal to home users and to small organizations because of its lower implementation cost.
All of the foregoing standards use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing.
Applications
For most organizations wireless LANs are expected to be used primarily in locations where pulling cable is difficult and expensive. Examples include single-story buildings on concrete slabs and multi-story buildings with no plenums (space between the floor and the ceiling of the floor below it, and landmark buildings with surfaces that cannot be disturbed. Another application is where the installation is intended to be temporary--thus making it possible to remove and relocate the wireless LAN at modest cost.
The accommodation of network users who move around a facility with a notebook computer or a PDA is another reason for implementing wireless LANs. While that includes areas of libraries, even more common are student union buildings, cafeterias, airports, and coffee houses. As notebook PC and PDA users become accustomed to connecting to wireless LANs, rather than to data jacks, they can be expected to demand wireless LANs everywhere, including libraries.
One of the most popular applications of wireless LANs in libraries has been the lending of laptops to patrons for their use throughout the building. That is not only an excellent way to increase the number of available PCs during busy periods without installing a large number of data jacks, but also gives the library the opportunity to configure the machines to best work with its automated library system and other electronic products and services. One library has learned that students studying as a group like to take several laptops into a group study room that has only one data jack so they can work collaboratively. Another--one with extensive book stacks-- has observed students using laptops on the floor in the classifications of interest to them. They can then search and retrieve very quickly.
Patrons, especially students, often bring floppies so they can download information, therefore, most libraries which make laptops available do not disable the floppy drives. They do limit access to the hard drives, however.
Costs and Headaches
Each access point costs up to $1,000 in equipment, plus another $1,500 for installation--a figure that includes connection to the electrical supply and to the organization's wired network. Each wireless adapter costs approximately $100. The individual PC cards are under $200. These prices are expected to drop as a large number of 802.11a and 802.11-conforming products reach the market and vendors of 802.11b products struggle to retain market share.
Wireless LANs take more time and expertise to design than wired networks. Very thick concrete floors, a large number of metal desks and filing cabinets, densely filled book stacks, and a large number of people can all weaken the radio signal.
Carnegie Mellon University, an early adopter of wireless LANs, spent six years experimenting and redesigning to adjust to all of the constraints before deciding that it would deploy wireless LANs campus wide. Among the important discoveries it made was that for 802.11b wireless LANs to work optimally, the operating frequencies of the access points must be spaced out evenly among the eleven allotted sub-frequencies or "channels" in the 2.4 Ghz range to prevent signal contention and performance degradation.
Larry Glover of the William F. Laman Public Library in North Little Rock, AK described the mistakes and missteps he experienced in the March 2001 issue of Computers in Libraries. He suggested measuring the building to get the spacing of access points right, computing bandwidth needs based on the potential number of users, and identifying potential obstructions to the radio signal before beginning the installation of the access points.
Although the libraries that have invested in laptops have generally purchased expensive machines with extended maintenance warranties, there have been a large number of maintenance headaches. Floppies often get stuck in the drives and drives are damaged in users' frantic efforts to remove them. This often requires returning the entire unit to the manufacturer. The hinges, which attach a monitor to a chassis, also break regularly. The batteries also do not hold up under heavy use and constant charging and discharging. The general rule-of-thumb is that a laptop costs two to three times as much as a desktop PC, lasts one-third to one-half as long, and requires three to four times as much repair over its life.
Prospects
Despite the enthusiasm about the new 802.11a standard, wireless LANs do not appear to pose an immediate threat to conventional wired LANs. While 30 Mbps may seem like a great deal of bandwidth, a large number of organizations are upgrading their wired Ethernet LANs from 10 Mbps to 100 Mbps because they have found that the increasing use of graphics, audio, and motion video on LANs means that it must be possible to provide each user with up to 1 Mbps of bandwidth.
A cluster of desktop machines or laptops in a small area can overwhelm a wireless LAN offering 30 Mbps or less of bandwidth. Finally, the users will be the ones to determine whether they will use wireless LANs exclusively. Rensselaer Polytechnic Institute, which for several years has required each student to own a notebook computer, expected that requirement to reduce the demand for student computer labs, but it has found that students often don't want to add a notebook to an already heavy book bag, or don't want to risk theft of the laptop. Students are also less inclined to upgrade memory and software on a regular basis than the institution. That is probably true of non-students as well.
More Information
Libraries interested in pursuing wireless LANs should search online reference services under headings such as wireless LANs, WLANs, wireless local area networks, wireless communication systems, and 802.11. Proxim, a vendor of wireless LAN product, has maintained a relatively up-to-date site at www.wirelesslan.com. Bill Drew of SUNY at Morrisville hosts a listserv entitled LibWireless at http://people.morrisville.edu/~drewwe/wireless/libwireless.html
There is an excellent technical article in the December 17, 2001 issue of Network Computing entitled "Mobile & Wireless Technology" beginning in page 27. Much of the article is devoted to mobile applications. An electronic version of the article has been available at www.networkcomputing.com, however, it may be removed to make way for other information at any time in the future.
When searching for information, it is best to look for that which is dated 2001 or later because earlier information does not reflect the current state of wireless LAN technology.
June 2002