A Field Guide to Wireless LANs for Administrators and Power Users

With WLANs, finally a networking technology has been designed that matches the way people use laptops. It is likely that the large extant pre-existing population of potential users (i.e., laptop owners with spare PC Card slots) enabled the rapid adoption of WLAN technology as soon as the first "fast enough" (up to 11 Mbps) cards became cheap enough for mass-market adoption. Based on the rapid acceptance of these products, the market was clearly ready and waiting for them.

So, wireless has the edge in convenience, but will probably always fall short in terms of ultimate performance.^[6] Luckily, in order to be successful, WLANs need not be fastest (or even as fast as wired LANs), just "fast enough to be useful." The most common application in today's home networks is to inexpensively and conveniently extend Internet access to machines throughout the house. Given that typical broadband access download speeds are only on the order of 750 kbps or so (perhaps as high as 1.5 or 1.6 Mbps), the 11 Mbps speed of today's most common WLAN technology is more than adequate (for this application).

^[6] As compared to a switched Ethernet LAN, which is often configured to dedicate at least 10 Mbps to each user (frequently 100 Mbps), as opposed to sharing 11 Mbps among all the active users as is done in IEEE 802.11b.

Applications of WLANs

These initial WLAN products were indeed fast enough to be usable, but not fast enough to be a wired LAN replacement. However, WLAN connectivity has become an ideal complement to a wired LAN connection. WLAN technology has become an integral part in most laptop product lines, even to the point of being integrated across the board.

Corporate Deployments

Wireless has become very popular with business users, and many corporate networks have installed WLANs to complement their wired LANs. Initial deployments were in places like conference rooms, but for convenience reasons, the deployments tended to spread. One good aspect for users is that they can simply install and manage their own WLAN by attaching a wireless bridge to a free network jack in their cubicle.

In fact, it is so easy to deploy WLAN technology that corporate IT departments need to have tools with which to patrol their networks in search of unauthorized wireless hubs. (There are security implications when naive end users expose the corporate network to eavesdroppers that may be sitting and listening in from their position outside in the parking lot.)

The ease of deployment is very good for users, and mimics the way that wired LANs appeared in corporations in the late 1980s and early 1990s; in other words, enthusiasts who were operating outside the boundaries of the MIS department installed them.

However, due to security aspects of wireless networking, this easy deployment of WLANs is very bad for the MIS department, since WLANs are often installed inside of the corporate firewall, which exposes the corporate network to unauthorized users. It is possible to deploy (currently proprietary) WLAN products with better security, but such products are often tightly integrated into a user authentication database to provide strong authentication and better forms of encryption than the basic WLAN product offerings; this integration causes an added load on the MIS department if they never had such a user authentication database in the past. Understanding the topic of security and WLANs is very important, and therefore it will be explained in detail later in the book.

Wireless "Hot Spots"

Besides corporate deployments of WLANs, by MIS departments and otherwise, there is an emerging industry in which enterprising companies providing public WLAN access have begun setting up wireless "hot spots" in places where business users congregate, such as airports, hotels, and conference centers. Wireless "hot spots" also tend to be near universities. In Cupertino, CA (home of Apple Computer and De Anza College), there is a donut shop called the Donut Wheel (open 24 hours, every day, even Thanksgiving and Christmas) that is renting out its airspace to such a service provider. Anyone with a WLAN-capable device can purchase 24 hours of Internet access for $2.00 which sounds like a bargain to me. Companies that operate such "Internet over WLAN" access services may sometimes be known as WISPs (i.e., wireless ISPs).

There is an interesting market segmentation that is possible (even desirable) in the relationship between the hot spot operator and the actual WISPs. In practice, many WISPs may want to provide access in the same local geographical area. However, there is a limit to how many non-overlapping channels exist within the various RF bands over which WLANs operate, and if every WISP installed its own local wireless infrastructure, they would all interfere with each other, and none of their customers would be able to use the services that the WISPs were trying to offer.

In the wireless access business, there is a natural place for a third party to exist, a "WLAN provider" that actually installs and manages the local physical infrastructure, over which the WISPs' customers access their respective WISPs. There is no directly analogous separation in the wired Internet access business, primarily because a single party owns the wires over which the service is offered, and because only a single customer can use a given physical facility at a time.

The WLAN operator would need to have a way of communicating with the various WISPs that have contracted with it, so that only valid users can gain access to the otherwise public airwaves.^[7]

^[7] Luckily, such protocols do exist, and are already being employed to a certain extent in enterprise networks; for example, the same protocols that corporations use to validate their dial-up users' identities can be (and will be) applied to WLANs. The topic of authentication will be covered in detail in the chapters on WLAN security.

Note that although a number of companies are trying to set up such businesses, there seem to be just as many local anarchists who are setting up free WLANs. Yes, you read that correctly, free. As in open access, no charge, high-speed Internet service. While many different companies have expressed interest in building and operating WLAN-based wireless Internet infrastructures from the traditional telephone companies, to wireless phone providers, to local ISPs, and others it is not clear whether the "free wireless access" movement will be a minor annoyance or a real impediment to turning WLAN-based access into a profit-generating venture.

Deployments at Home

Another ideal usage scenario for WLANs is in the home, since most houses do not have networking jacks in every room, and WLANs just use the air that most people already have at home in abundance. Even though the natural platform for WLANs so far has been laptops, it is also possible to add a WLAN interface card to a standalone PC. In fact, the typical home PC is probably not a laptop, at least at this point in time. Trends in the business world tend to repeat themselves at home, so it is likely that laptops will become increasingly prevalent at home, eventually. In 2002, and into 2003, the largest portion of the WLAN market, based on revenue, was due to home-based WLANs, to the extent that over two-thirds of the revenue was attributable to home-based WLAN deployments.

Other home-networking technologies have been created, including the Ethernet-like products from the Home-Phoneline Networking Alliance (HomePNA^™[8]). Despite being able to perform the technically difficult trick of operating Ethernet over the telephone wiring in a house, the fact remains that there is a practical obstacle that must be overcome there aren't telephone jacks in every room of the house.^[9] Moreover, the HomePNA^™ network is a shared network of approximately the same speed^[10] as 11 Mbps WLANs (and 54 Mbps WLANs are already on the market). Therefore, the fact that WLANs do not require any physical changes, such as additional wiring, is a big advantage for most home users.

^[8] For more information on HomePNA^™, go to www.homepna.org.

^[9] To have an extra phone jack added to my residence, the author paid a handyman over $100 to climb around in my ceiling, find the phone wiring, drop a new extension down between the walls, and install a wall jack. Adding more than a few extensions to an existing telephone system can be rather expensive.

^[10] HomePNA^™ products can achieve between 1 and 10 Mbps of throughput, although future versions will be faster. The actual speed will depend on the quality of the existing wiring, how much noise is on the lines, and other factors. However, future HomePNA^™ will continue to suffer from the fact that it will still be a shared medium, and it will still be limited to use by devices that are near telephone jacks.

The one downside for WLANs in the home is that most homes have many walls, and drywall is fairly opaque to 2.4 GHz radio waves (even more so to 5 GHz RF radiation). Empirical data suggests that for each wall that a 2.4 GHz RF signal must pass through, it loses between 20 and 35 percent of its signal strength. Consequently, after passing through at most four walls, there will be virtually no remaining signal over which to provide wireless connectivity. One way to solve this problem would be to strategically locate a small number of additional wireless base stations, which are more properly known as "Access Points" (a.k.a., APs) throughout the house. Deploying APs is considerably easier than adding additional telephone or network jacks, although the APs will need to be attached to a wired network.

One network topology that can be very useful at home is to have a WLAN "backbone" connecting little islands of wired connectivity, as in Figure 1-1, which depicts one such island. Note that it is possible that the AP functionality may one day be integrated into the PC itself (e.g., Microsoft's rumored "Soft AP" implementation). It is also conceivable that, given the right software, any WLAN card could enable a PC to become an AP.

The WLAN demonstrably has sufficient bandwidth to enable the users in a home to share broadband access to the Internet. In the future, more bandwidth-intensive applications, such as network-based audio and video distribution in the home, may require that higher-speed WLANs be used, perhaps in conjunction with expanded wired LANs if the applications' demands cannot be met with a purely wireless infrastructure.

For now, the most interesting application and the speed available are a good match for each other. In fact, as indicated in Figure 1-1, newer models of Home Gateway devices are often sold with an integrated AP.