Script: Wireless LAN audio primer

Wireless LAN technology offers a pair of enticing promises: You no longer have to drop cable to every desktop and your users can connect from just about anywhere on your campus. However, making it work is not as easy as just putting up an antenna and installing some new wireless-Ethernet cards. In this primer we'll take a look at the alphabet soup surrounding wireless LANs, how they work, and some of the challenges involved in implementing them.

Most wireless-LAN activity these days centers on a group of similar specifications: 802.11, 802.11b, 802.11a and 802.11g. All are designed to replace Ethernet cables connecting clients to a LAN. We'll discuss the variations in a moment.

An 802.11-based LAN can be set up in two ways: peer-to-peer (or ad hoc) and client/server. In the peer-to-peer model, 802.11 clients running the same specification can talk with similar clients in the general vicinity. This setup is good for mobile LANs. The client/server model involves a wireless access point that acts as a bridge between the wireless clients and the wired LAN. If two access points are located near each other, they must communicate on different channels in order to avoid radio interference.

The benefits of letting users roam seem obvious - think of users creating impromptu connections from a conference room, or of doctors gaining roving access to patient records. But there are pitfalls and issues to consider first.

First, the further away from an access point the less powerful the signal to the client, meaning less bandwidth. Also, this is radio, meaning walls, water, people, air temperature, humidity and many other atmospheric conditions can affect how far and well a signal will travel. Lower frequency signals have easier time passing through objects than higher frequencies.

For these reasons, a site survey is necessary for plotting where to position access points in a multi-access point environment. Remember that two neighboring access points cannot run on the same channel. A client moving between access points on different channels can be problematic, but there are software solutions that can help solve the problem.

Also, wireless LAN products broadcasting at 2.4 GHz do so around the same frequency as common appliances such as microwaves and some cordless phones. These appliances can emit radio waves that interrupt or degrade the quality of the wireless LAN signals.

One technology designed for the consumer market, HomeRF, gets around such problems by using frequency hopping, but it is not compatible with 802.11-based products.

Security is also an issue. A wired LAN has the physical protection of a building and restricted entry. A hacker must be physically connected to the network in order to access it. The wireless LAN signal can travel outside a building and can be picked up by anyone with the correct equipment. Also, unauthorized users could access the network by using a compatible wireless Ethernet card. The term "war driving" is used to describe those that drive around town looking for open (intentionally or unintentionally) wireless networks.

The Wired Equivalent Privacy (WEP) protocol, used in 802.11-based implementations, has come under attack because it's easy to crack. WEP was only designed to give wireless transmissions roughly the same protections as wired connections; mainly keeping the casual user out, not necessarily the sophisticated hacker.

One way to keep an unauthorized user from using a corporate wireless network to access company secrets is to separate the wireless network from the wired. Employees connecting over the wireless network can use standard VPN software to access corporate data. However, this method can be difficult to manage if a large number of users are connecting wirelessly. Also, the VPN protects only the data, not the network itself.

Encrypting wireless data and requiring users to authenticate themselves before being able to access a wireless LAN are the two biggest roadblocks one can put up to help keep the unwanted out. Products are available that sit between the access point and the wired network that can handle these tasks. Also, the IETF is working on the 802.1x specification for authenticating users connecting to a wireless LAN.

Even with the basic setup covered, there's still the matter of picking which wireless LAN technology to use.

802.11b, adopted by the IETF in 1999, is the leading standard at the moment. It provides 3 separate channels in the unlicensed 2.4 GHz range, providing up to 11M bit/sec of connectivity - a more-than-adequate speed to support most business applications. 802.11, the original specification ratified in 1997, provided 3 channels of just 2M bit/sec wireless connectivity using part of the unlicensed 2.4 GHz radio spectrum.

To ensure interoperability between different vendor implementation, the Wireless Ethernet Compatibility Alliance developed Wi-Fi, a base standard for 802.11b devices. This allows companies to use a Wi-Fi-certified access point from Company A with certified wireless Ethernet cards from Company B.

802.11a was adopted around the same time as 802.11b, but that's where the similarity ends. 802.11a operates up to 13 channels in the unlicensed 5 GHz range and can provide up to 54M bit/sec of connectivity. It uses a broadcasting technique that breaks a signal into multiple sub-signals to help avoid interference. 802.11a products are just beginning to enter the marketplace.

802.11g is still under development. Like 802.11b, it uses 3 channels in the 2.4 GHz spectrum but is said to deliver data rates up to 22M bit/sec using the same signal-splitting technique. Also, 802.11g will be backward compatible with 802.11b. Currently, 802.11 endpoints cannot see each other unless they're adhering to the same specification.

HiperLAN2 is a European standard that competes with 802.11a. It runs in the 5 GHz range and proponents argue that it can sustain throughput of up to 42M bit/sec. The HiperLAN2 specification includes a number of quality-of-service (QoS) provisions giving priority to certain types of traffic, such as voice or multimedia.

Bluetooth is sometimes thrown into the wireless LAN debate, but its intention is to be a cord-replacement technology. Instead of running a USB or parallel cable to your printer, you could use Bluetooth wireless technology to make the connection. It also can be used by a cellphone to share data with a PDA without the need for a PC as an intermediary. Bluetooth's transmission range is only 30 feet, compared with 300 feet or more with 802.11b products.

Currently, most products sold in the wireless LAN space are based on the 802.11b specification. Enterprising users looking to boost signal range beyond 300 feet have built antennas using such common household items as a Pringles chip can wrapped in wire. Beware though when installing antennas on the roof of a building. Wireless network guru Rob Flickenger severely injured himself after falling two stories from the roof of his home while trying to install 802.11b equipment.

While 802.11b is the leader today, more technology is in the pipeline to make wireless more robust and secure with QoS features built in to guarantee mission critical data. For many companies, wireless LANs are still an accessory, not a necessity.

For more on wireless LAN technology, visit our Wi-Fi research page.

Back to the main Wireless LAN Audio Primer page

RELATED LINKS