|Tech Notes |
By David Masters
The reason for the surge in wireless popularity is the IEEE’s 802.11b standard and the Wireless Ethernet Compatibility Alliance’s (WECA) “WiFi” certification process. WECA is a consortium of wireless manufacturers that has certified and guaranteed interoperability among 802.11b products since mid-1999. The 802.11b standard has increased the throughput of wireless LAN hardware from 1.5Mbps to a much more practical 11Mbps, and has led to the availability of standard off-the-shelf radio chip sets, bringing the price of wireless networking hardware down dramatically. You can now find 802.11b wireless PC cards selling for as low as $59. Wireless access points (WAPs), which connect wireless users to the wired LAN, sell for as little as $150. Just a few years ago, those prices were $700 for cards and $2,500 for WAPs. Communication between 802.11b products occurs via the 2.4GHz radio band using direct sequence spread spectrum (DSSS) technology, which spreads transmitting packets across the 2.4GHz band for security purposes and to prevent interference, and then reassembles them.
Two other wireless networking standards have also come onto the scene. The 802.11a standard offers connections speeds of up to 54Mbps. Communication between 802.11a products occurs via the 5GHz radio band. Accordingly, “a” and “b” products cannot communicate with one another. Several manufactures have produced “dual band” products.
More significantly, the recently developed 802.11g may become the prevailing and unifying standard. It offers the speed of 802.11a, but operates on the same radio frequency as 802.11b and is therefore backward compatible with those devices, so that an existing 802.11b network can be upgraded to 802.11g without incurring the expense of upgrading all computers on the network at the same time. Computers operating on the 802.11b standard can continue to use the same equipment and use the 802.11g access points (but only at the 802.11b speed of 11Mbps). Computers equipped with 802.11g cards will communicate at 54Mbps.
A completely wireless network can be a viable solution for a small office. For performance reasons, however, most office LANs use wireless as an extension to the wired LAN. For these environments, you need two types of hardware: wireless network interface cards, which fit into the PC card slots of notebooks and PCI slots of desktop computers; and WAPs, which aggregate wireless radio signals and connect roaming users to the wired LAN. Both act as receivers and transmitters. The cards are identified as Ethernet adapters by the system. Most vendors let you purchase optional higher-gain external antennas to get better signal strength. These are particularly useful for desktop PCs and areas with physical obstruction problems, but can be somewhat cumbersome.
The WAP acts as a translator between the wired LAN and the radio link. Each WAP is about the size of a hardcover book and contains a radio transceiver, communications and encryption software, and an Ethernet port for a cable connection to a hub or switch port on the wired LAN. As a wireless user sits or moves about, the radio transceiver in her system’s wireless network interface card finds the nearest WAP and negotiates a connection speed based on signal quality. The further you go from an access point, the lower the signal quality, so in large spaces you’ll usually have to connect several WAPs to the network. WAPs offer a feature called “roaming,” which transfers the user’s radio connection to another WAP as she moves out of range of the first. Roaming allows wireless LAN users to wander the hallways and even move between floors while remaining connected to the network.
Most wireless LAN solutions come with site survey and configuration tools that help you place the WAPs appropriately and configure IP addresses, station names, and other parameters. You should generally place WAPs high up, in clear open areas. The range of each WAP depends on the construction and layout of the surrounding environment. You’ll usually need to place them a few hundred feet apart in clear spaces and as little as 50 feet apart across walls and ceilings. For environments with large numbers of users, you can add WAPs operating on different channels, or frequencies; many let you configure up to three or four separate channels.
Keep in mind that as with wireless LAN cards, WAPs with external antennas are likely to have signal strength about 15 percent greater than those with internal antennas, and since you can move the antennas into positions that avoid obvious obstacles, external antennas may yield far superior performance. As a result, if you opt for WAPs with external antennas, you’ll likely need fewer than if you use WAPs with internal antennas.
You may not think security is a major concern, but if you’re running a wireless LAN in an office building, don’t be surprised if someone using their wireless LAN in the building across the street can browse your network. In more open areas, a hacker could easily enter your LAN from a nearby parking lot. There are a few ways to prevent this. One way is to take advantage of the option that lets you assign each card a seven-digit security code, called an SSID. Anyone without the appropriate SSID will not be granted access to your LAN. Most products also let you create access control lists based on Media Access Control (MAC) addresses.
In higher-security environments, you’ll also want to take advantage of encryption, but be aware that you’ll be dealing with more management overhead. All WiFi products can use the Wireless Equivalent Privacy (WEP) specification, which scrambles wireless data using encryption. You have to configure WEP both on the WAPs and on each of the clients, a time-consuming process that usually requires setting keys on every device. Vendors offer various levels of encryption, so be prepared for tweaking and troubleshooting if you try to use it in a network of devices from more than one vendor. Otherwise, cards and WAPs from multiple vendors should be able to communicate with each other with few problems.
The principal vendors of wireless LANs are 3Com, Belkin, D-Link, Intel, Linksys, and Microsoft. You can expect performance to be roughly equivalent among the products, with the main differences being the kinds of configuration and management software they provide, as well as the levels of security encryption that they support. For small office environments, some vendors also provide combination WAP and Internet access routers.
David Masters ( firstname.lastname@example.org) is a sole practitioner in Montrose, Colorado. He is a frequent speaker on legal technology and the law and a member of the Editorial Board of GP Solo’s Technology & Practice Guide . David Masters is filling in for Tony Vittal in this issue, due to a death in Mr. Vittal’s family.