Week of July 20, 2006  

// Network Computing Mobile Observer Weekly Newsletter
\\ Your Mobile and Wireless Resource
// Powered by CENT
\\ http://www.networkcomputing.com/mobile
// 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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