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Putting the 'enterprise' into wireless LANs

Tolly on Technology By Kevin Tolly, Network World
April 12, 2004 12:04 AM ET
Tolly

Network World - As wireless LANs have rocketed into the consciousness of corporate managers in the past year or so, existing and prospective vendors in that space have been quick to point out how not to build a WLAN. Stay away, they say, from the temptation of building your network using a shopping cart full of those $100 access points from your local Circuit City. Enterprise WLANs need more. Recent examples prove the case.

While a basic, single access point WLAN servicing a handful of clients is simplicity itself, expanding that network with a second access point to handle a few more clients over a little larger area causes an immediate spike in complexity.

With one access point, roaming is a non-issue, selection of the radio frequency channel for the access point is mostly arbitrary, and performance is likely far less important than just the ability to work untethered. Scaling to enterprise level, though, these and other issues arise. Some can be resolved with overprovisioning and careful RF planning. Others require technology solutions that go well beyond what can be had in "plain vanilla" 802.11b/a/g standard gear.

Two recent projects of mine, although hardly the only examples, provide some good insights into the types of innovation that are defining true enterprise-class wireless solutions.

Like AirespaceMeru, NEC and some others, Airflow Networks has a vision that is tightly coupled with the emergence and integration of voice and wireless. The company sees both hard-wired VoIP traffic becoming wireless and the majority of our mobile phones soon becoming equipped with 802.11 technology and being able to hop onto our corporate LANs.

With voice on the network, the issue of roaming - your WLAN traffic being handed off from access point to access point as you move about the building - becomes critically important. Where the signal degradation and "re-association" process of "standard" roaming are of little consequence when you're walking down the hall with your laptop under your arm, they can be more than a nuisance if the wireless device is a phone at your ear.

To deal with this, AirFlow completely rethought the access point implementation process (among other things). The company's "distributed access point" approach lets many distributed radios appear to the client as one access point. This, coupled with intelligence that lets AirFlow's WLAN switch determine the best radio to use at any moment, removes the re-association need from the clients along with providing hand-off between radios without packet loss that is below 10ms even under load. Thus users are assured enterprise-class handling of their voice-over-WLAN calls.

Meanwhile, wireless chip vendor Engim has focused on a severe but little-recognized performance bottleneck inherent in all previously available standards-based products. And it is one that only gets worse as WLAN speeds increase. A recent Network World Fusion story provides details.

Engim's essential insight was that at any given instant, overall throughput of a WLAN access point was throttled by the transmission speed of its current user. With 802.11g systems being able to service, say, 802.11b clients that were at the fringe of its coverage, that communication could be taking place at 1M bit/sec. And because clients of access points were rarely all in "optimal" range, some degradation was likely always taking place. By using three channels at once, and separating out users into their appropriate "lane," Engim increased overall access point throughput by up to 50 times.

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