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May 7th, 2010
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Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity Learn how to avoid wireless interference problems and speed WLAN troubleshooting with Cisco expert Jim Florwick. Jim has over 20 years experience in the design, integration, and maintenance of wired and wireless communications networks. Florwick joined Cisco as part of the Cognio acquisition in 2007. He is a member of the Technical Marketing Engineering team for Cisco’s Wireless Business Unit.  Florwick has been focused on Radio Resource management (RRM) and CleanAir product development.  Prior to Cognio, he designed and deployed mission critical networks for many Fortune 500 enterprises and leading organizations through his senior consulting positions at NCR, AT&T and Ventus Networks.

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Overall Rating: 4.9 (6 ratings)
Leo Laohoo Fri, 05/07/2010 - 22:48
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Hi Jim,

I'm really interested about ClearAir technology.  I understand from the Data Sheet that the 1260 and 3500i/3500e are supported on the 7.X firmware.  Do you know when is it scheduled for release?  What platforms will support CleanAir?  Is CleanAir enabled by default (just buy the 3500i/3500e only) or will there be license option involved?

jiflorwi Mon, 05/10/2010 - 10:03
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Hello Leolaohoo,

Orderability for Cisco 3500 series products should be turned on by the end of May 2010.  Thanks for your interest, it is a great product.


jiflorwi Mon, 05/10/2010 - 10:14
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Sorry about that - a bit quick on the trigger.

Launch details are located here:

Licensing is based on system compomnents and levels.  At the base level - a Cisco 3500 AP and a controller running version 7.0 code wil provide full view of current CleanAir information and supports the full mitigation features as well as Spectrum expert connect feature.

Adding WCS will allow historical reporting of AirQuality metrics and monitoring of security related IDR's (Interference Device Reports).  As well as inclusion of a CleanAir Dashboard and trending information with regards to AirQuality.  This is available with the WCS base license.

Adding the MSE to the system provides a great deal of functionality including historic Interference specific reports, and location (current and historical) of interference devices.  The MSE requires that WCS have a plus license - and will also require CAS (Context Aware Sevice) license seats for the individual interference targets.

At present there will be free CAS licenses offered with bundles of 3500 series AP's, up to 100 seats for 20 AP's.  Release date of the 7.0 software is targeted for the end of May as well.


Leo Laohoo Mon, 05/10/2010 - 18:43
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At the base level - a Cisco 3500 AP and a controller running version 7.0 code wil provide full view of current CleanAir information and supports the full mitigation features as well as Spectrum expert connect feature.

Hi Jim,

Perfect!  and music to my/our ears.  +5

eric nguyen Fri, 05/14/2010 - 05:27
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Would you mind expanding on:

At present there will be free CAS licenses offered with bundles of 3500 series AP's, up to 100 seats for 20 AP's. 

Bundles refer to. . . 10 packs? What are the conditions of "up to 100"?  Does that scale up - if I purchase 100 APs, will I get 500 free CAS licenses as well?

jiflorwi Fri, 05/14/2010 - 10:01
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Hi Eric,

My bad, yes by bundles I mean 10 Pak's.  The MSE will automatically recognize the first 20 AP3500's on it's network and apply 5 CAS licenses per AP up to 100 total.  The license stays with the MSE - and if you remove a 3500 - and only have 19 on the network the license count will drop by 5 to 95 total.

This is additional licenses to any that already exist.


skronawithleitner Tue, 05/11/2010 - 23:40
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hi jim,

2 questions:

* (not a question about cleanair per se, but related) regarding the new AP 3500e, which uses external antennas - is it possible to mount this thing on a wall? (and by "possible" I mean possible like with the 1250, not "possible, but with strong disadvise" like the 1140). At many locations it is difficult or even nearly impossible to mount an AP on the ceiling. If yes, in what directions do the antennas have look?

* about cleanair: Is it wise to change channels so quickly? neighboring APs will then have to change channels also (because of the only 3 channels in 2.4ghz band), and then the neighboring APs to those, and so on. Wont this kick off an avalanche through the whole building, disrupting service for clients even far away from the noise source? some clients need some time to pick up on channel changes... I'm not saying that we should never change channels, but that fast in a big building with more than one interference source could trigger a channel change in the whole building every minute?

thanks for enlightening me,


jiflorwi Fri, 05/14/2010 - 07:42
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Hi Stefan,

A most excellent question - and thank you for asking that!

for question 1 -Can I mount the 3500e (external antenna) on a wall?

Yes!  With the foillowing caveats.  You will need to use the articulated diploe antenna's.  Mount the AP so the label is read correctly and change the polarity of the antena's so the outside two for each radio is up and down respectively.  The center antenna for each radio can be horizontal or vertically polarized - see photo:

On Question #2 - this is a very very good question - and the answer is a bit detailed - my apologies in advance but it takes a little background to answer properly.

With EDRRM - is it wise to change channels so quickly?  Won't this force all neighboring AP's to change channels and cause a cascading effect accross the infrastructure?

First - RRM is a centralized algorithm - not decentralized to operate just at the edge between AP's like some of our competitors solutions.  RRM runs on the RF group leader and manages individual RF domains - or groups of AP's that can hear one another.

Since version 6, the DCA algorithm has been updated to address the needs of every increasing AP density to operate on multiple local searches involving the target AP needing adjustment - and it's first RF hop neighbors all of which may have their channels changed to effect a solution.  The second RF hop neighbors are included in the target cell, but channels on these may not be changed.  Multiple channel plan simulations are run on this group and the effect of the entire cell must be an overal improvement in throughput for the cell in order for a channel plan to be implemented.  That's the fast version of the base algorithm - but it prevents a cascade chanel change from ever occuring.  It also gives us very granular control over a local cell grouping of AP.s and allows us to optimize for a group - not just a specific AP since this could be detrimental to it's neighbor.  The good of the whole is considered.

Now - for ED-RRM the channel change will only occur if the Air Quality is sufficiently impacted.  Since Air Quality can only be affected by a classified known to CleanAir non- wifi source of interference - we know that the impact is 1.  Not a Wi-Fi anomoly, and 2. A crisis condition at this AP.  By that I mean that CCA is blocked - no clients or the AP are able to use the current channel.  Under these conditions RRM would change the channel on the next DCA pass - however that could be a few minutes away, or the user could have changed the default interval and it could be longer.

ED-RRM will react very quickly - so the users that change with the AP - will likely be un-aware of the crisis that was upon them.  The users that do not - are in no worse shape than they would have been in the first place.

The channel change - is not random - we pick based on device contention - so it is an intelligent alternate choice.  Once the channel is changed - there is protection against triggering ED-RRM again in a hold down timer (allowing users to catch up), the abandoned channel is also marked in ED-RRM for this AP to prevent a return in the event the interferer is an intermitant event and DCA does not see it immediately.  IN all cases the impact of the chanel change is isolated to the affected AP.

Again - this is only triggered based on the AQ threshold selected by the adminsitrator - and would be a catastrophic event for all users of this radio-channel.


Leo Laohoo Sun, 05/16/2010 - 02:54
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You will need to use the articulated diploe antenna's.

Hi Jim,

Is the Cisco Aironet Very Short 5-GHz Omnidirectional Antenna (AIR-ANT5135SDW-R) and Cisco Aironet Very Short 2.4-GHz Omnidirectional Antenna (AIR-ANT2422SDW-R) compatible to the 3500e?

CSCO11256353 Mon, 05/17/2010 - 01:52
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-      for a wireless survey what are the most important factors to keep in mind

-      Does cisco wireless device porfolio includes anything which can work in temperature range of   -30 centigrade to 0.

-      can we use an outdoor wireless AP as an indoor using dipole antennas.

Thanks in advance

jiflorwi Mon, 05/17/2010 - 14:00
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I will answer these questions inline -

-      for a wireless survey what are the most important factors to  keep in mind

The most important factor to keep in mind is the application requirements.  In all network architectures there are core applications that form the business critical sute that will have to be served.  What these application require to operate will be the guiding factor to what it takes to support this on wireless.  Unfortunately, in most cases this is poorly represented in the survey.  Once you have this, determining the inimum coverage and throughput required to support it is a match argument - followed by validation with live RF and measurement.

-      Does cisco wireless device porfolio includes  anything which can work in temperature range of   -30 centigrade to 0.

Yes - several products designed for extreme duty include -

1300 Series Bridge      -22º to +131ºF (-30º to +55ºC)

1400 Series Bridge      -30º to +55ºC (-22º to +131ºF)

1520 Series Mesh        -40 to 55°C (-40 to 131°F) plus Solar Loading

Other Access Points designed for manufacturing and carpeted areas are not designed for mounting directly outdoors and
Therefore the temperature ranges are typically in the range of
-4 to +131°F (-20 to +55°C)

To use these products in colder environments a heated NEMA enclosure should be used.
Such NEMA enclosures can be purchased from their party sources such as <>

-      can we use an outdoor wireless AP as an indoor using dipole  antennas.

That depends on the Access Point and the RF connector present on same.
The 1300 Series Access Point/Bridge has RP-TNC connectors so one can use dipoles on such as device.
If the device is say the 1400 eries of 1520 series the Dipoles will not attach as those products use an “N” style connector and the Dipoles use “RP-TNC” style which is not compatible.

jiflorwi Mon, 05/17/2010 - 05:28
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Yes they are.  And it makes a very nice installation.  However, the polarity of these anten

na's is not adjustable and they should be reserved for ceiling mount installations.

Leo Laohoo Mon, 05/17/2010 - 16:53
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Thanks Jim.  (+5)

rasullivan Thu, 05/20/2010 - 12:48
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Hi Jim,

During a today's episode of TechWise TV “Improving Air Quality with Cisco CleanAir” we were notified that mixing in 3500 series WAPs with legacy 1140/1250 series WAPs is not advisable if the 3500s are in local mode, only monitor mode. The "Cadillac" as they called it was to have a pure 3500 series environment and configure them all for local mode. That wont work for us as we have recently complete a one for one upgrade for 2600 WAPs. Now we are in the process of redesigning for density rather than coverage and want to use the 3500 series to back fill our network.

Can you tell me why mixing the legacy and 3500 local mode is not advisable? I dont completely understand the EDRRM vs RRM aside from the basic point of the 3500's automatic interference avoidance being done on the WAP and RRM being done by the group leader.

Any info would be greatly appreciated.



jiflorwi Thu, 05/20/2010 - 14:31
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HI Ryan,

Thanks for your question.  That was me on the techwise TV show by the way ;-)

I do understand the issue quite well and am sensative.  It is not that you can't mix these AP's - it is that you will need to understand what you will - and will not get and set that expectation for the management of your network.

There are two  operational modes for a 3500 series AP that are important here -

Local Mode - or LMAP (local mode AP) in which we are servind a chanel that has client traffic on it

Monitor Mode - or MMAP (Monitor Mode AP) in which we are a deidcated listening device

In local mode - we are continuosly listening to the served channel - if the AP is operating on channel 6 - then CleanAir is restricted to channel 6.  Off Chanel scanning is disruptive to client traffic, and as such we restrict it in operation.  For CleanAir, off channel scans do not have the repetition rate - or duration required to be of much use, so we do not use them.

If you itegrate CleanAir AP's into an existing deployment in LMAP mode - this is how the AP will function.  Now - AirQuality and interference information will all be valid - however the density of the Spectrum AP's is likely to be too thin for meaningful information to be coordinated.

If the AP's are adminsitered by RRM - then RRM will assign channels to the 3500 series AP's as it does for the legacy AP's, and there is no gurantee that you will have a 3500 on each channel required to watch te whole band.

So - is there a benefit to installing 3500 series AP's in an established environment in the LMAP mode - I think yes - but t comes with risk.

Yes - because you have the ability at anytime to convert the AP into a monitor mode AP and do full spectrum monitoring and troubleshooting.  This includes using the AP as a remote spectrum Sensor for Spectrum Expert.  These are nice features to have handy - and saves a lot of time in getting to the bottom of things.  If there is a wide band interference source - one that affects all or many channels, you will get alerted.  If on the other hand you experience a narrow band interference source - you could well have no knowledge of this if none of the 3500's are operating on the affected channel at the time.

The Risk - There is that nothing in the system that would alert you to the fact that you are not really watching the whole band - and someone who does not know the demployment details could reach an incorrect conclusion if they rely on the flashy screens in WCS.  Severity of the interference source - is now possibly a red herring - seeing something with a low severity would not convey a sense of urgency.  Severity takes into account the proximity of the AP to the source energy - by that i mean you could see a video signal (100% duty cycle) but be so far from it that severity only comes up at 10 or 12.  In this example - you would want to be very alert to any interference - and work to locate the source and evaluate it.

Now - a MMAP or Monitor Mode AP, was designed with this in mind - and depending on density of the overlay - will provide the full spectrum details.

As an AP - the 3500 will integrate with other AP's.  The mode and density will either contribute or detract from the CleanAir system resoultion.  Understanding these caveats - is critical to setting expectations.

I do hope that this helps.  We do not want you to pass on the 3500.  Let me ask this - is it possible to re-deploy some of your existing AP's to increase density in a given space - and deploy the 3500 seria AP's in a pervasive mode to cover potentially a critical space?  I know that means more work - but it might be worth considering.


rasullivan Thu, 05/20/2010 - 15:06
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Thanks for the reply Jim. Our senior engineer was quick to point out that you were great at the wireless demo/seminars at networkers last year

To answer your question, I am not sure management would fund a redesign in such a manner because while the information we would get to troubleshoot and better understand the RF environment is nice, it doesn’t give the clients more bandwidth (well directly anyways).

Our first generation wireless system was a mix of the Avaya AP3 (b) and AP8 (a/b/g) WAPs that grew in an ad hoc fashion to cover a good portion of the campus. At the time, we ran everything at full power and focused on providing coverage. That set of hardware was fine when wireless was just a cool thing to have available but as you know better than anyone, the legacy products do not lend themselves to mission critical network access.

So, at the time we were attending the various pitches from marketing and sales teams we were turned on to the idea of replacing these units with the 1252s on a one for one basis as we would not incur the cost of recabling thousands of locations. This forklift took over a year and we ended up with 15 WiSMs, 2 MSEs, WCS and a few spectrum experts.

Since we have noticed that the legacy design has flaws like stacked units and too few units we have seen a ton of RF related issues which RRM has told us about. Management has been made aware of these issues and supports increasing the density of wireless across the campus. We are currently in the position of wanting to purchase and install roughly double the WAPs that we have right now (2600 right now) over the next few years.

I was very excited to hear about the clean air product but I am not sure that we will get to use the full feature set. I assumed that the 3500s had a separate radio to perform spectrum analysis rather than sharing the radio and moving the functionality into chipsets.

I would like to bring a few other folks into a conversation about the Clean Air products. Obviously, you are the man to talk to so can I set up a conference call or better yet a webex with you directly or should I ask our SE and WNBU guys?

Once again, I greatly appreciate your time.

Thank you,

Ryan Sullivan

Datacom, ACT


jiflorwi Thu, 05/20/2010 - 15:14
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Hi Ryan,

It was not my intention at all to sway you from the 3500 AP - I just wanted to be clear about the functionality limitations in such a deployment.  I do think that there is tremendous benefit in having the resources on site - instead of needing to roll a truck when there is an issue.  I know from experience (I have not always been a VENDOR) that getting good solid information in a timely manner can decrease the overall user impact greatly.

Regardig your question on further discussions.  I would prefer that you reach out through your SE, that way we all stay in the loop.  I am happy to have a discussion though.


mubeeshalivm Fri, 05/21/2010 - 05:47
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so in short cisco clean air is supposed to

be an enahanced RRM with more capabilities to isolate  issues like interf erence (wifi and non wifi ) and  we can do wireless captures as well;

I guess wireless captures can be performed from a cisco AP in monitor/sniffer  mode ; so why clean air ?

.... We have 30 controllers , a WCS and  location appliance. still not into wireless N ...does it have any means for  airtime fairness when there is a mixture of clients (say like b and g clients ; may be include N clients as well for the sake of others who are running N )

Thank You,


rasullivan Fri, 05/21/2010 - 12:24
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The Clean Air products are providing a view of the spectrum, not just 802.11 traffic. Basically, it would show you non-802.11 sources of interference.

jiflorwi Fri, 05/21/2010 - 14:08
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Hello Mubeesh,

CleanAir is not an enhanced RRM.  It is a spectrum management application based in high resolution hardware.  One of the benefits of this is integration onto RRM and better metrics and mitigation capabilities.

This provides a detailed view of the physical layer that can not be gathered by a Wi-Fi modem.

For 802.11n and legacy (802.11a/g) client performance there are features such as-ClientLink and Bandselect

Client Link uses beam forming to enhance a legacy OFDM client SNR by as much as 6 dB

Bandselect encourages dual band clients to use 5 GHz - effectively.

Airtime fairness is a science and depends on what applications you are intending to run.

All of these require good physical layer chracteristics to be efficient - and this is even more true once you increase the speed to 802.11n rates.



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