WIRELESS THAT WORKS
By Rahul Sukumar, Senior Network Specialist
You've spent an entire year rolling out a campus-wide, ultra-redundant, high-capacity,
ultra-secure wireless network. You followed best-practice guidelines in regards to access
point placement, density, and security. Additionally, you had the wireless vendor double-check
your implementation plan. But something's just not right… Your users are complaining of
dead spots, poor performance, and dropped connections - definitely not something you expected
from an enterprise-class system! Looking into the configuration of your switches, access
points, and wireless devices only leads to dead ends. What could be wrong? Below you will find
some not-so-obvious solutions to common wireless woes.
Dead Spots
The most obvious cause of dead spots is lack of RF coverage, but simply adding more access
points in a trouble area may not be the best solution. Strategic placement of access points is
more important than one might think – changing the angle of an antenna by 30 degrees may
be enough to shed more RF “light” down a dark hallway.
Antenna types also play a big role in determining coverage. Using an AP’s built-in
antenna in a long, narrow corridor might be less effective than using an omni-directional
antenna mounted horizontally on a wall.
Poor Performance
Numerous factors can affect the performance of your wireless network including weak signal
strength and low-end hardware in your devices. But RF interference may be the single biggest
drag on throughput (and one of the easiest to fix). You’re probably familiar with the
usual culprits of this bothersome phenomenon (microwave ovens, cordless phones, etc), but
it’s also important to remember that your network may be interfering with itself.
Although the FCC has allocated 11 channels to the 802.11b/g standard, just 3 of them are
completely non-overlapping. If you have 3 access points in a room, and assign them channels 1,
6, and 11, no interference will occur. However, adding a 4th access point to the mix will force
two of these radios to fight for the same frequency, resulting in a substantial performance hit.
And depending on their sensitivity, your wireless devices may get confused by the interference
and drop their connection altogether. Using a wireless monitoring tool, such as NetStumbler,
will allow you to analyze the number of access points your wireless client can see in a given
area (and which channel those APs are operating on). Even if your pre-installation site survey
planned for low interference from neighboring access points, traditional methods used during
the survey likely ignored interference from radios located on adjacent floors. Manually
adjusting power levels and channels on access points can help reduce interference, if not
eliminate it.
Keep in mind that wireless networks are only as strong as their weakest link. For example, if
you have placed an access point on the 8th floor near a window that overlooks the park,
wireless devices may successfully connect to your network from several blocks away. However,
since signal strength at that location will be very weak, clients that connect will be forced
to use extremely low data rates, effectively slowing down everybody else while the access
point “waits” for that one slow client. Solving this problem could be as simple as
changing a setting within your access point or wireless switch: set the minimum allowed
connection rate to 50% of the maximum.
Dropped Connections
Like poor performance, dropped connections can occur for any number of reasons. Some are
relatively obvious (interference, for example) but some are a little harder to identify.
Dropping a connection while a device is stationary can be indicative of a hardware problem.
Flashing to the latest firmware and/or upgrading device drivers could improve stability.
Dropped connections while roaming, though, are especially frustrating. Assuming you’ve
already ruled out hardware problems, configuration errors, and interference, try using multiple
wireless network cards from different manufacturers to see if the problem is consistent among
different chipsets. Intel® wireless chipsets, commonly integrated into Centrino® based
laptops, have been widely reported to suffer from “sticky-client syndrome” where
the device fails to roam to another, closer access point even if it’s currently
associated AP is several hundred feet away.
The authentication/encryption mechanisms you employ on your WLAN will also have a significant
impact on a device’s ability to roam seamlessly. WPA encryption with 802.1x
authentication, for example, must go through multiple steps before successfully associating
with an access point. If problems are encountered during any one of these steps, authentication
will fail and the whole process will start over again, leading to connectivity interruptions.
You could solve this problem by moving to a quicker authentication and/or encryption method,
but you’ll be compromising the security of your network. Thankfully, emerging standards
are on the way to help resolve these issues without sacrificing security. WPA2, based on the
802.11i amendment to the 802.11 standard, has certain provisions that should greatly improve
security and roaming ability.
Wireless networks will probably never be as reliable as their wired counterparts. But after a
fair amount of tweaking, you can get pretty close; and building a stable WLAN for data devices
today will help ensure reliability of future applications, such as wireless voice and location
tracking. For more information on wireless technology, visit the WiFi Alliance’s website
at www.wi-fi.org. Of course, you can always contact your
friends at VCS as well!
CUSTOMER CORNER: PALMETTO HEALTH
“Between the pre-work, onsite assessment and easy to understand reporting tool, the
value resulting from the VCS HNAM Tech Flash Assessment was un-surpassed” says Jeffrey
Douglas from Palmetto Health, the largest healthcare provider in South Carolina. As the
Director for Strategic Systems and Operations, Jeff and his team support over 6000 end users.
They were looking for an independent assessment of their Cerner system including the front and
back-end, storage and Citrix® systems in order to keep their Information Systems running
as efficiently as possible.
Palmetto Health chose Vitalize Consulting Solutions, Inc (VCS) to perform the assessment
precisely because they were looking for an independent, unbiased opinion coupled with
recommendations that the Palmetto team could implement. “The concept behind the VCS Flash
Assessment is to provide significant recommendations in order to bring hospitals closer to a
best practice model, at a price far below that of traditional assessments” indicated
John Smaling, VCS Principal. “By benchmarking against more than 100 best practices all
at a price under $15,000, we feel that we’ve accomplished that”.
Jeff adds, “The technical team was phenomenal. They brought incredible backgrounds to
the table and because of that, they assessed much broader and deeper than any other resource
we previously used or considered.” The VCS certified Senior Systems Consultants stay
current on Cerner, Citrix®, IBM WebSphere®, Oracle, Storage Optimization and more in
order to provide positive outcomes for a predictable price.
Learn more about the VCS HNAM TECH FLASH ASSESSMENT by clicking the link below or call
Kim Tombragel at 405-752-0590.
http://www.getvitalized.com/marketing/techflashes/techflash1.htm
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