Back to Basics
Posted: 06.01.05 - By Lamont Wood


Deploying a wireless local area network (WLAN) in your office can seem complicated, with the user facing an avalanche of cryptic names, such as 802.11g, WPA and AP. But the concept of a WLAN, or Wi-Fi, is actually simple, and the hardware involved in setting one up should not scare away potential users.

Basically, you are extending your Ethernet LAN into the air, using short-range, low-power radio frequency (RF) transmissions, so network users don’t have to plug their devices into an Ethernet port as they move from room to room. The client devices have typically been laptops with Wi-Fi radios, but Wi-Fi use has spread to barcode readers, PDAs, industrial and medical equipment and even special telephone handsets that use Voice over Internet Protocol (VoIP).

Stripped to its bare essentials, there are really only three things you need to install wireless Internet access:

1. An existing LAN with a free port on one of its routers or on a cable leading back to one of its routers. (The ports of most Ethernet routers offer at least 100Mbps connections, which, as I’ll explain, is sufficient.)

2. A Wi-Fi access point (AP) to plug into that LAN.

3. A client device with Wi-Fi circuitry compatible with the AP. (Almost all laptops sold these days include Wi-Fi circuitry. Intel promotes the Centrino chip as the workhorse on the client side, but there are plenty of other devices that do the same job.)

For a home or small office network, these three may be all you need, except for security settings, explained below. Plug everything in and you should be able to get online from anywhere up to about 300 feet from the AP (although your throughput will drop with distance and the presence of physical barriers such as concrete, brick or steel walls.)

Once you go beyond this simple, ideal situation, you have to worry about multiple users and multiple APs, additional AP features, the demands of additional applications—and, indeed, multiple Wi-Fi formats. Next, we’ll look at Wi-Fi formats and AP features. Then we’ll examine features of more specialized Wi-Fi installations.

Pick a Flavor, Any Flavor

There are currently three Wi-Fi formats, named for the technical committees of the Institute of Electrical and Electronics Engineers (IEEE) that codified them: 802.11b, 802.11a and 802.11g. To simplify things, I’ll just use the initials..11b—Despite the secondary initial, b came first and offers an official speed of 11 Mbps but an effective throughput (due to overhead) of 7 Mbps. This is still faster than the cable or DSL modem available to most home users.
.11a—Has an official speed of 54 Mbps, but an effective throughput closer to 23 Mbps.11g—The speed is the same as a, but g operates at a different wavelength.

Most clients still support b, and most APs these days support all three, so choosing which format to use is rarely an issue. (The next format will be n, offering about 200 Mbps, but don’t expect it for another two years.) What’s likely to be an issue is the extra features supported by the AP, such as security and management.

Circling the Wagons

Security is an issue for both home and office users. Unless the security settings are used, the AP and clients will communicate openly, and eavesdropping and unauthorized network access are both possible. Security for Wi-Fi has gone through several generations; the latest (WPA2) came out in fall 2004 and is said to be as good as anything available for a landline.

Authentication provides a second level of security, often seen in enterprise networks, that assigns the level of access a specific user will be given. (Not everyone gets to see personnel files, for instance.) Enterprise-level APs may offer authentication, but the function may also be handled elsewhere in the network.

Enterprise-level APs (which typically cost several times more than home APs) can also be expected to offer remote management features, to monitor the network and allow intervention when problems arise. Such service is usually provided by off-site contractors, leading to a need for remote control.

Unplanned-for APs often pop up at a workplace, typically when an employee brings one from home—instantly creating a security hole. Specialized RF devices can be bought that will constantly sniff for rogues. There is also specialized software that can scan for unexplained Ethernet ports, and there are enterprise-level APs with rogue detection features.

Multiply, Multiply

As for how many people can use an AP at any given moment, the rule of thumb is about 25 with b and somewhat more with a and g—if they are doing ordinary Web surfing and e-mailing, explains Lynn Lucas, VP at Proxim, a wireless networks company in Sunnyvale, Calif. Barcode scanners in a warehouse send only small bursts of data, and a hundred such users might be able to share the same AP, she explains.
Recently, enterprises have discovered they can hand out VoIP Wi-Fi handsets to roaming employees and avoid cell phone subscriptions. However, using a Wi-Fi network for voice adds new demands to its APs. Chris Vuillaume, VP of Alcatel’s Voice Enterprise Group, says that he sometimes has to tell network managers that their Wi-Fi setup is simply not suitable for voice traffic. He lists four attributes that the APs should have for successful voice: Quality of Service (QoS), hand-overs, roaming and security.

QoS features ensure that voice traffic receives priority treatment. Hand-overs mean you can move from AP to AP while talking, and roaming means that call handling is the same across multiple sites. QoS is a recent addition to the Wi-Fi standard. Work is under way on standards for hand-offs and roaming, but in the meantime the features are based on the vendor’s proprietary software, Vuillaume notes. Security features, of course, prevent eavesdropping.

Regardless, accumulated tiny delays in obtaining access will eventually cause jitter in the voice traffic, and an AP used for VoIP will become unusable after more than seven to ten voice users are added, Lucas warns. Video may actually be less of a problem than VoIP, since the eye accepts many defects, and video streams can often be highly compressed.

Mixed Signals

Another issue in enterprise networks is signal range, which depends on many factors: Sheet rock and drop ceilings are nearly transparent to RF, but glass, brick and filing cabinets may cause problems. The layout of any Wi-Fi network must be kept flexible to accommodate for the discovery of dead spots.

In a large controlled space with many barriers but a limited number of users, the best way to boost coverage may not be to add APs but to boost the power of a single AP, indicated Tony Stramandinoli, director of marketing at SMC Networks in Irvine, Calif. Most APs ship with a transmission power of 100 or 200 milliwatts, he says, but government regulations allow signal strength of one watt—enough to carry through three floors.

“If you have a 10,000-square-foot building, one watt and one AP will let you light up the entire building and for 1,000 feet outside,” says Stramandinoli. An add-on amplifier and antenna for the AP will usually do the job, but then the more remote users will need to boost the power of their client devices in order to communicate back to the AP. Most Wi-Fi adapter cards use 35 to 50 milliwatts, but adapters are available that use 200 milliwatts. However, Straman-
dinoli warns that battery life will be proportionally lower.

Another special-purpose device used in wide-area settings is a bridge, to connect APs to each other and to the network when a cable is not available. Usually these are actually .11g APs that have been altered so they communicate only with other bridges and not with client devices, he adds, and they typically cost as much as an enterprise-level AP.
For really large-scale coverage (such as a municipality turning itself into a hotspot), you need special antennas.

For instance, Vivato in San Mateo, Calif., offers phased array antennas that focus the transmitted radio energy into multiple beams that are sent in specific directions, explains Vivato VP Dan Vortherms. Each beam is only 9 degrees wide but each constitutes a standard Wi-Fi signal, and the users do not need any special equipment. Mounted on roofs or cell phone towers, they can cover an area that would take 25 local APs. However, such devices weigh about 80 pounds and prices start at about $10,000. Ranges of up to 10 miles are possible, but the users will need a signal booster on their client devices in order to reach back to the antenna, Vortherms explains. Ontario-based BelAir Networks also makes outdoor, large-area Wi-Fi coverage a possibility with its 100 and 200 radio systems.

Finally, there are the cables, which need to be strung between the APs and the router. (Some APs have two ports, so you can daisy-chain them to each other instead of connecting each AP through a dedicated cable to a single port on a router. One port should be able to handle four APs that way.) In offices the cable is commonly strung above the drop ceilings and through the air ducts and plenums. But cables routed this way should have a “plenum
rating,” says Carl Blume, director of marketing at Colubris Networks. The rating means they will not emit dangerous fumes in case of a fire, and that makes them cost a little more.

Indeed, going wireless doesn’t necessarily mean there will no longer be any wires running through your office, but if you do it correctly, there will definitely be fewer wires. And, you’ll be able to hop onto your enterprise’s network from places you couldn’t before.•

 


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