Avoiding WLAN Set-up Headaches (Part II)
December 03, 2001
Part two of our in-depth analysis of what IT managers need to know about planning for and setting up a successful 802.11 network
Building WLANs that really work may not be as easy as it's cracked up to be, as we started to discover last week in the first part of this two-part primer on design and implementation.In Part I, Jesse Frankel, chief strategy officer and vice president of advanced technology at Akron OH WLAN integrator NeTeam Corp. (www.neteam.com), pointed out some of the wires that all too often trip up first-timers.
Readers who took in last week's 802.11 Planet conference in San Jose will also remember Frankel as a panelist in the "Building & Equipping Wireless Networks That Work" session. This week, he takes us through some of the basic step-by-step process of designing and installing a successful WLAN.
The first set of steps - and as in most IT- and communications-related projects, it's absolutely crucial - is gathering and analyzing requirements.
"You have to make sure that all of the real-life usage requirements are well understood," Frankel says. "One thing we harp on is understanding users' performance expectations. A lot of people may not have a totally realistic idea of what can be achieved. And then we also run into a lot of people who haven't thought about the question at all."
This goes back to an example Frankel used last week of a training room where 30 users may all need to connect at once over the WLAN. If the room is only within range of one access point, users will not get the performance they expect.
You also have to look at the existing wired infrastructure, he says - assuming the WLAN is an extension of or overlay on an installed wired LAN - and ask what new equipment, if any, and what integration effort will be required to make LAN and WLAN work together seamlessly?
Then there are constraints and restrictions related to the physical infrastructure and the environment. What are the building materials and how will that effect propagation if at all? And where is it permissible to install antennas and access points in the facility?
"Sometimes there can be aesthetic requirements," Frankel notes. "You don't see it so often in office settings, but if you've got an executive floor, people sometimes don't want antenna masts sticking out through the ceiling, for example."
Another set of questions about requirements bears on security issues. In many installations, you may need optimum performance near the perimeter of the coverage area. But without careful design, that can result in coverage extending well beyond the perimeter - up to a half mile outside the building in some cases.
"This is something that is generally not well understand," Frankel says. As witness all the stories about hacktivists cruising up to office buildings and easily hacking into the corporate WLANs inside.
There are ways to solve such problems using pico-cell architecture, employing low-powered access points. It's even possible to engineer a WLAN that will provide good coverage in one area - a boardroom say - but no coverage at all in an insecure adjacent area such as a lobby.
"This phase of the requirements collection and investigation is where a lot of the competency comes into play," Frankel points out. "Much of the effectiveness of [NeTeam's] process is the result of [what we do in] this initial phase."
Another aspect of requirements gathering is understanding cost objectives. There are costs outside the price of the access points themselves and the cabling.
One important question is how easy or difficult - expensive or inexpensive - will it be to get power and Ethernet to the access points? The answer determines where and how you can deploy access points, but you have to ask it early to avoid cost over-runs later.
In the best-case scenario, there is a power outlet near every location you need for an access point. When that isn't the case, there is a range of possible solutions, Frankel says.
Some, though not many, Ethernet switches enable transmission of DC power over CAT-5 Ethernet cabling. So now all you have to worry about is getting Ethernet to the access point. It's also possible to buy add-on hardware for Ethernet switches that in effect "squirts" power down existing CAT-5 cabling to the access point.The most expensive way always is to hire a union electrician to put AC current into the location, Frankel notes.
"Sometimes that's a design criteria," he says. "They say, 'You can put 'em anywhere, except you have to put 'em within 10 feet of an electrical box.' In terms of deployment, it's one of the often overlooked pieces. But it's important because guess what? You have to plug these things in!"
Another consideration when it comes to deployment of access points is network management. Good network-based management systems have never been available for WLAN's, Frankel points out. The best diagnostic tools are often the blinking lights on the access point hardware.
"So it's nice to have the access point in a spot where it's easy to see," he says. "And definitely not up in the ceiling or any place that takes ladders and keys to get at it."
Exact positioning of access points to meet primary coverage and performance requirements as well as these other criteria is ultimately determined by a site survey - a to some extent trial-and-error process that involves setting up a temporary access point and systematically measuring the coverage it provides by exchanging test transmissions with a mobile client device.
One of the keys to effective site surveys, Frankel says, is testing for performance as well as coverage. "Always measure coverage by probing the test access point with the largest possible data frame. And you need to set up a symmetrical link between computer and access point."
Also worth noting: site survey results will differ markedly according to which vendor's equipment you use. It may be the same base technology, even in some cases the same chip set, but there are wide differences in coverage characteristics in both network interface cards (NICs) and access points. Different transmission power levels, different NIC antenna designs, for example.
"Some places when they buy Cisco or ORiNOCO equipment will get [the vendor's] site survey utility and use that casually," Frankel says. "Then six months later, they switch cards or add cards from another vendor, and they don't work. A lot of people don't realize how widely RF performance differs from vendor to vendor."
If you're not standardizing on one network interface card or one access point vendor, you must do the site survey using the lowest-common-denominator products - the devices with the poorest coverage characteristics.
Antenna selection is also critical in determining exact positioning of access points. Different antenna designs produce different propagation characteristics. It's a topic Frankel clearly believes is beyond the ken of novices, another area where his company has special expertise.
"It's something we've invested in a lot, gaining knowledge of the specific behaviors of many different antennas," he says. "We have relationships with many antenna vendors and we've been involved in helping design antennas too."
Frankel offers two more tips on successful WLAN design. First, make detailed documentation of the physical layout of the network in the design phase - right down to orientation of antennas, which an be critical. Why? Because designers may not always be able to closely supervise installation.
Finally, do periodic checks on network operation after the installation.
"This is another key element we build into our processes," Frankel says. "WLANs are living breathing organisms. They never stay the same forever. You need to check periodically just to make sure they don't have problems in the making or problems that haven't been noticed yet."
Sometimes when NeTeam does such post-installation checks it finds components broken or missing. While many companies now view WLANs as critical infrastructure, there is still the attitude in some that you can just install it and forget it, he says.
All of this may leave you thinking that you need a NeTeam to design and install your WLAN. It's always a consideration, of course, as with any project: do you go out and acquire the knowledge yourself, perhaps painstakingly, or buy the expertise you need.
The real point is just this: designing and implementing a WLAN should not be undertaken lightly. It is, or can be, a complicated thing. There, you've been warned.