// Network Computing Mobile Observer Weekly Newsletter
\\ Your Mobile and Wireless Resource
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// Wednesday, July 19, 2006
When IT and Execs Work Together, Success Ensues
Listen to this Emerging Enterprise podcast and discover how an IT director for a
pharmaceutical distribution company ensures his IT group works hand in hand with
executives to provide competitive advantage and grow the business.
http://www.networkcomputing.com/blog/dailyblog/archives/2006/06/emerging_enterp.
html
Look for our next Network Computing Mobile Observer newsletter on
Wednesday, July 26, 2006.
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In This Issue:
1) Wireless Propagator: A Wireless Repeater to Switch Transition? -- Part 2
2) Mobile & Wireless Commentary
3) Mobile & Wireless News, Opinion and Analysis
5) Mobile & Wireless Product Watch
5) Calling All Readers
6) Resource Tools
7) Subscription Information
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1) Wireless Propagator: A Wireless Repeater to Switch Transition? -- Part 2
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By Frank Bulk (mailto:fbulk@nwc.com)
A few weeks ago (
http://www.networkcomputing.com/mobile/archives/mobile_archive_062806.html ), I
discussed the challenges of dense wireless deployments and some of the ways to
address them. Micro-cells, or APs (access points) with smaller coverage areas,
are one way to re-use the existing spectrum more times within the same
geographical area. The two chief side effects of micro-cells are higher
co-channel interference and power asymmetry. A four-channel design in the
2.4-GHz range can reduce the incidence of co-channel interference, but it
introduces adjacent channel interference because the channels overlap. Generally
this has been avoided, but after reading my last column, Aruba informed me that
it was able to identify more than 20 clients using the four-channel design.
Finally, there is a single-channel design that depends on a controller to
'coordinate' access among APs.
Serving dense numbers of handsets--or terminals, as cellular operators describe
them--builds from spectral planning. Important elements include antenna
placement, channel selection, output power and antenna design, which result in
certain patterns. When consumer cellular service was launched in the late 1970s,
wireless carriers deployed an omni-directional antenna with a single radio on
tall towers at high output power to serve the few 'mobile' phone users. Once
service became more affordable and mobile phones more popular, operators
switched to multiple radios with sectorized antennas at lower output powers,
adding many more of them to take advantage of spectral re-use.
Wi-Fi infrastructure vendors are moving along the same evolutionary path as
cellular providers, albeit on a smaller scale. As I mentioned in my last column,
dual-radio APs have been available for quite some time, but the reality is that
the 5-GHz band is generally underutilized. Where capacity has been a challenge,
micro-cells are deployed. But the last step of the path, multiple sectorized
antennas integrated into one AP, has just started to happen.
Two vendors offer a poly-radio access point: Xirrus, with its Wireless LAN
Array, and Meru Networks, with its Radio Switch. But the distinctive design of
each choice results in different capabilities.
Xirrus offers three differently scaled models: a 4-, 8- and 16-radio access
point. All models start with four 802.11a/b/g radios and add more 802.11a radios
as they are scaled up. Just under 19 inches across and 4 inches high, the
circular unit has multiple radios, each serving a narrow but slightly
overlapping arc of coverage. Because it's difficult to create sufficient RF
isolation between radios at such close range, even on nonoverlapping channels,
coordination occurs on the MAC (Media Access Control) layer. As a result, the
radios take turns receiving and transmitting so the transmitted signals don't
get distorted and the receivers desensitized. The directional antennas deliver
higher gain so they can transmit farther, which means fewer APs (or arrays) need
to be placed. This, in turn, reduces deployment costs. With good channel
planning, co-channel interference can be reduced because the signals are not
broadcasting omni-directionally. But narrow coverage patterns likely mean more
roaming events--a problem for most VoWLAN (voice over WLAN) deployments. In
short, the Xirrus array excels in reducing cost by either eliminating multiple
installation points or eliminating the requirement to deploy multiple APs in the
same physical area.
The Meru Radio Switch also comes in three models: a 4-, 8- and 12-radio access
point. Most deployments will likely operate two or three radios in the 2.4-GHz
range for 802.11b/g service and the remaining ones in the 5-GHz range for
802.11a service. Besides Meru's Air Traffic Control technology, which leverages
its own MAC to provide predictable service and QoS, the Radio Switch
load-balances traffic across the various channels. The Radio Switch goes so far
as to ignore probe requests from clients that should be on another channel. In a
dense wireless environment--at a convention center or in lecture hall, for
example--hundreds of users can be served for as little as $350 to $400 a radio.
Unlike Xirrus, which uses a separate directional antenna for each radio, the
Meru system has two omni-directional antennas inside a shell, one antenna
dedicated to transmitting and the other to receiving. Each antenna is located at
the other's 'null,' or dead, spot to assist in isolating the RF. And each
radio's RF output is actually combined in the access point and separated on the
input. Without directionality, the antennas don't extend coverage like Xirrus.
But co-channel interference isn't a problem for Meru because its single-channel
technology coordinates AP transmission across cells. Rather than place a second
and third AP to increase capacity, the Radio Switch can be used to serve
high-user densities.
Detractors of wireless switch designs point out several weaknesses: increased
cost per AP with a centralized versus a distributed investment, greater power
draw and real-world effectiveness. To the first point, it is true that the cost
per AP will be higher; but the cost per radio will be lower. And will every
install use every radio? As I bemoaned earlier, 802.11a sees very little usage,
so most environments might start off with a 3-channel 802.11b/g design with a
single-channel overlay of 802.11a. But if serving a dense population is actually
important, businesses will mandate--and educational institutions will gently
encourage--users to take advantage of the 5-GHz range.
On the second point: The additional radios do draw more power, so the poly-radio
vendors offer three options: use local AC power; use a special adapter to draw
power from multiple PoE (Power over Ethernet) ports; or use a custom power
injector from the vendor. Both Meru and Xirrus are sensitive to the power draw
issue. With so many radios, the maximum 15.4 watts of service that the IEEE
802.3af standard defines is insufficient. Fortunately, PowerDsine is leading
vendors to the next generation of PoE, called PoE Plus, which will roll into the
proposed IEEE 802.3at standard and certainly double, if not quadruple, power
output.
The last jab issued by critics of the wireless switch is real-world
effectiveness or practicality. Are these AP designs too niche to enjoy
mass-market adoption? Meru introduced the Radio Switch over a year ago but only
recently started shipping. Although the customer has not been publicly
announced, the company claims one school system has purchased thousands of Radio
Switches. Xirrus announced a strategic alliance with ADC a few months ago and
has won several awards. The company shared with me three public wins
encompassing 36 arrays (equivalent to about 276 APs). It will take time to work
out any bugs, add features and gain customer acceptance, but it's admittedly
this last critique that runs true. Perhaps these vendors are a little ahead of
their time and organizations haven't faced the intensely dense deployments found
now only in open lecture halls and public areas such as libraries.
Next time, I'll write about advanced antenna solutions that don't necessarily
use multiple radios but are able to enhance performance and coverage and,
sometimes, total capacity.
Frank Bulk is a contributing editor to Network Computing Magazine covering
wireless and mobile technologies and works for a telecommunications company
based in the Midwest.
For more analysis and opinion from Frank Bulk.
http://www.networkcomputing.com/channels/wireless/
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2) Mobile & Wireless Commentary
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a) Air Time: Wireless FUD--Alive and Well
By Dave Molta
The wireless network market is an industry that lives and dies by innovation, so
fear, uncertainty and doubt are all things we have to learn to live and work
with.
http://www.networkcomputing.com/channels/wireless/showArticle.jhtml?articleID=19
0302833
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3) Mobile & Wireless News, Opinion and Analysis
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a) Wireless Standards: A Future Without Cables
By Dave Molta
Expect to see an array of wireless systems tied together by higher-layer
standards like IMS. Integrating those technologies in a way that allows a wide
range of devices to move transparently across networks won't be easy. But as
standards evolve, that hope is likely to be realized.
http://www.networkcomputing.com/channels/wireless/showArticle.jhtml?articleID=19
0302864
b) Cisco Wireless Bugs--Deja Vu?
By Lee Badman
Bugs were recently found in Cisco's Wireless Control System that appear similar
to past problems affecting its Wireless LAN Solution Engine. In each case, fixes
required new code. But the real solution should have been vigilance.
http://www.networkcomputing.com/channels/wireless/showArticle.jhtml?articleID=19
0303113
More mobile and wireless news.
http://www.unstrung.com
http://www.nwc.com/netnews
http://www.techweb.com
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4) Mobile and Wireless Product Watch
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a) Review: Netgear XE104
By Ron Miller
You can simplify home networking with this 85-Mbps wall-plugged Ethernet switch,
but not without some compromises.
http://www.networkcomputing.com/channels/wireless/showArticle.jhtml?articleID=18
5300203
b) Radio-Tested WLAN Clients
By Dave Molta and James Blandford
We tested Wi-Fi implementations in notebooks from market leaders Dell, HP,
Lenovo and Toshiba to assess how the interaction between different clients and
access points affects system performance.
http://www.networkcomputing.com/channels/wireless/showArticle.jhtml?articleID=18
0206318
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5) Calling All Readers
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a) Beyond Print
What kind of podcast do you like to listen to? Do you like to hear a host rant
for 20 minutes? Do you like debates? In this week's episode of his ongoing
series, NWC's Mike DeMaria reviews the four major podcast formats: scripted,
monologue, debate and interview. He discusses the advantages of each, situations
that make one more appropriate than the other, pitfalls and potential ways to
ruin each format. If you would like to subscribe to the NWC podcasts, please
subscribe to our podcast RSS feed. It'll let you get all the new episodes
automatically.
http://www.networkcomputing.com/blog/dailyblog/archives/2006/07/beyond_print_07.
html
b) Review: Firefox 2 Takes on IE7
By Preston Gralla
The beta of Firefox's next version doesn't have any radical changes, but it does
include a few nifty tweaks. Can it continue to challenge IE?
http://www.NetworkComputing.com/showArticle.jhtml?articleID=190500228
c) The Network Computing Expert Series: Remote Office Management
Spend one morning with us and master the decentralized enterprise. You'll gain
valuable information and strategies on architecting and managing your companies
distributed networks. Coming to a city near you! We'll be in Boston, on October
31, New York City on November 3, Chicago on November 7, and San Francisco on
November 9.
http://www.networkcomputing.com/events/remote/
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6) Resource Tools
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a) Mobile and Wireless Channel
Find mobile and wireless news and commentary by industry experts
Dave Molta,
Peter Rysavy and Frank Bulk on our Mobile and Wireless Channel.
http://www.networkcomputing.com/channels/wireless
b) Read More Mobile and Wireless Stories on TechWeb
http://www.techweb.com/tech/mobile
c) Missed an Issue of NWC's Mobile Observer Newsletter?
Have no fear. We've created an archive of back issues for your reading
pleasure.
http://www.networkcomputing.com/mobile/index.jhtml
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7) Subscription Information
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