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Cisco Wireless CleanAir Technology - FAQ : 3500 APs






This document is about the most recent generation of access points from Cisco and the integration of the CleanAir technology to locate and mitigate interferences. This information is used from recent Ask the Expert - Cisco Clean Air event by Nicolas.



Q1. What is the possibility of using the AIR-ANT2506 2.4Ghz bridge antenna on the AIR-LAP1242-E/AK9 AG Access Point in AP mode and the possibility of clients such as mobile laptops associating with this antenna, even at it's farthest coverage range

A. The antenna type AIR-ANT2506 is compatible with the 1240 series APs, as confirmed by Table 1-1 in the following official guide:-


As described in the initial note of this discussion, please note that this Q&A session is reserved for questions on the CleanAir technology.

1240 series APs and the AIR-ANT2506 antenna type have nothing to do with CleanAir: I would recommend to please look for recommendations on your questions through other more general CSC communities.


Q2. What Licence's are required to deploy Cisco Clean Air on WCS,WLC and MSE?

A. For WCS, you need WCS Plus.  If you purchase the eco-pack (a box of 10) of the 3500, the WCS Plus is free.

WLC- doesn't matter.

MSE - It's the usual context-aware license but just be aware that interferers count as clients.


Q3. To clarify on the WCS license. Is it true that you get the same AP count of WCS-PLUS license that you buy in the eco pack? For example, I am a new Cisco wireless customer and I buy a 10 pack of 3500i APs. Do I instantly get a 10 AP license of WCS-PLUS or is this simply an upgrade from 10 WCS-BASE to 10 WCS-PLUS? If this is truly a WCS-PLUS one for one license would that basically make WCS free for this type of customer?

A. When you take the eco pack, you get an upgrade license. This means it "upgrades" a normal WCS license to a PLUS license.

The good side is that with a 10-eco pack you get an upgrade for 100 APs.


Example :-

You have 90 1242s. You have a WCS-100 AP standard license.

You buy a 3500 10-eco pack. Your WCS license of 100 APS is used at the maximum of 100 APs. The free upgrade you received means you can have the PLUS feature with all 100APs.



Q4. Lets Discuss Few Different setups?


  • What functionality do you get if you only have a WLC and no WLC, MSE?
  • What functionality do you get if you only have WLC and WCS with just a BASE license?
  • What functionality extra do you get by having a WLC, WCS and Plus license?
  • What functionality extra on top do you get if you have a WLC, WCS and Plus license with the context-aware license.


Guess i am just trying to work out the difference in functionality between all set-ups so i know for each potential client what is required depend on what they require.  For some new client it might be good enough just to know that there is interference which is being picked up mainly by a certian AP but they are not to bothered about locating this on a map and will find it manually?

A. WLC alone, will be able to detect interferers. Here's an example of the "monitor->clean air" page :


AP NameRadio Slot#Interferer TypeAffected ChannelDetected TimeSeverityDuty Cycle(%)RSSIDevIDClusterID


So you can know what interferer it is, what are its characteristics at the current time. WLC will also send traps and syslogs accordingly

WLC can also give air quality indicators in order to average the quality of an area around an AP.


If you have WCS without the plus license, it's pretty much the same. You can't locate or have clean air stats in WCS.


With the plus license on WCS, you can locate the interferer and see the statistics through time with graphs, etc ... It also correlates the information sent by multiple WLCs if several APs saw the interferers and they are on different WLCs.


MSE will allow to track interferers in "real-time" (not exactly real, but close enough) on the map.


MSE will be the only device capable of merging Interferer Device Reports (IDRs) from different WLCs.

So only with MSE you won't run into the risk that an IDR for the same interferer detected by different WLCs is actually reported as two different interferers/IDRs (potentially possible when having multiple WLCs, but no MSE comparing data from those WLCs).



Q5. I know it's possible but I wonder if it is advisable to configure multicast on wireless network.


We have 3 WLC 5508 with code and Base license. we have over 160 AP's running N the clients are connected in a great big address pool - with possibility of 8000+ host ip's. we currently have over 1000+ clients connecting Management expects wireless to work like a wired network.


They want to enable multicast for applications like Apple Bonjour and other programs and also for streaming video. I am of the opinion it's not the greatest of ideas. I see people enabling multicast but not on the scale with the user base we have. any advise?


Also would there be any performance issues if clean air is enabled?


A. CleanAir is a separate chipset in the AP and detects interferences with a dedicated hardware, it can then not have any impact on AP performance at all. Now regarding multicast ... Let's first explain why it's generally not a good idea and finish with possible alternatives.


Over the air, a multicast is pretty much like a broadcast. In the sense that if an AP sends a multicast, it keeps the air busy for all the clients of that AP, so regardless of the amount of clients subscribed to the stream @ that AP, the performance will be the same.

Because of the horrible consequences if it was the case, the multicast frames are not ACKed by anyone. We're not talking about TCP ACK or anything but usually every single frame over the wireless is acknowledge between client and AP. That's the only way to know if there has been a collision or not.

So because there is no ACK, there is no retransmission. And because wireless is a shared medium, collisions do occur as normal part of the medium. So even in good conditions, there will be a bit of packet loss. In case you have external interferers or high number of clients, then the amount of lost packets will drastically increase and the stream performance is then not acceptable.

Furthermore, because the AP doesn't know how far are the multicast-subscribed clients located, it cannot know if the clients will be able to receive the frame at the maximum data rate (54,144 or 300Mbps). Maybe one of the subscribed client is at the border of the coverage cell and can only transmit at 24Mbps due to the distance. When doing unicast, this is acceptable because close clients get their data at 300mbps and only the far away client is talked to at 24Mbps but in a multicast, .... So as conclusion, the WLC will ALWAYS send the multicast stream at the highest configured data rate. Which is often between 1 and 24Mbps but rarely more.



On the solution side :

-Starting from 7.0 software version, the feature "DirectStream" is there to bring a possible solution. The multicast is still multicast over wired : so only the APs having subscribed clients will received the data. But over the air, the AP unicasts the stream to every subscribed clients.

Advantages : Retransmission are possible, data is acknowledged, data is sent at the fastest rate acceptable for that particular client.

Inconvenient's : If you have a lot of subscribed clients per AP it might not be good to unicast to all of them from a performance perspective. Direct Stream usually performs better than normal multicast with 7 or less subscribed client per AP.


-If you have a lot of clients subscribed to your multicast stream on each AP, the "normal" multicast may be your best choice. In this case, you can configure a much higher data rate as "mandatory" so that the multicast stream is sent more rapidly. But be aware that this prevents transmission of the stream to clients that would be a bit far from their AP.

Out of experience, the 2.4Ghz band is usually quite busy (only 3 channels, lots of devices, ...) and it's rare to see a good video stream on multicast over 2.4Ghz unless you are using DirectStream. On 5Ghz, it's quite feasible to have a good stream using the "normal" multicast.



Q6. I would like to know more on the statement called " This is an opportunity to learn about the last generation of access points from Cisco ". Does this means there will be no more new models?

A. The "last" in that sentence means "most recent" and not "there won't be any new one after this one". The expression "last generation of access points from Cisco" means that this is the latest/newest generation (so the last one as of the present day). It does not mean that this will be the last APs that Cisco will ever design/produce.


Q7. We have a few units coming in soon, but it will be a mixture of 1252's and 3500's.  Few Questions:

  1. Would there be any difference on M-Drive technology between clean-air and other AP's?
  2. Since the clean-air technology is based on hardware, can it be turned off as well, just to know?

A. 1) For everyone, the "M-drive" marketing term englobes the following :

  • ClientLink improves reliability and coverage for legacy clients
  • BandSelect improves 5 GHz client connections in mixed client environments
  • VideoStream uses multicast to improve multimedia applications


These 3 features are software features available also on non-cleanair AP models. So those feature stay identical on Cleanair AP models. No change at all.


2)Yes you can turn it off. On the WLC web page : "Wireless" - >802.11a/n -> Cleanair -> You have cleanair settings there and a general checkbox to disable it. Same goes for the 802.11b/g menu to disable clean air on 2.4 Ghz.


Q8. I understand that the spectrum analysis runs in parallel to the regular AP duties so that client connectivity can be maintained.  Can you explain the clock cyles involved in simple terms with regards to the AP going off-channel to detect interferers?  Also how this impacts clients, or if there is a hold-off period when the AP is busy?


A. CleanAir is run in parallel with standard client serving processes, so no need for the AP to go off-channel.


Interferers will be detected only for the same channel for which you are serving clients, if you are using a local mode AP.

If using a monitor mode AP, then the AP will cycle through different channels (without serving clients) and detect interferers on multiple channels.


Q9. So with regards to off-channel scans for say IDS?  Do these still happen? Another thought is regarding RTLS - will the AP assist with location of interferers that aren't on the operational channels?

A.  We can think of CleanAir as of a parallel feature set, but separate with regards to the previous "standard" features of other APs.

So for example, RRM off-channel scans will also still works the same as for other non-CleanAir APs.


For locating interferers, a CleanAir AP in local mode will definitely help to locate interferer, but only on the channel on which it is serving clients.

CleanAir APs in monitor mode can help locating interferers on multiple channels.


Q10. I am looking for the procedure to completly default a 3502i AP and reset the username and passwords. It has previously been associated with a controller at another clients site. All the documentation I have found so far outline procedures for older APs?

A. To reset an AP we could have different options.


1. Through the MODE button:


- Power off the AP.

- While keeping the MODE button pressed, power on the AP.

- Still keep the MODE button pressed until the Status LED turns to red and then release it:


This, however, may not fully reset the AP to its factory defaults.


2. By downloading the recovery image to the AP and let it reload after that. Through a telnet/console connection:


debug capwap console cli

archive download-sw /overwrite /reload tftp://<TFTP IP>/<recovery image path>


The recovery image for 3500 APs can be found on

Q11. I'm currently in the site survey stages of a 500 ap deployment (3502i and 3502e). We will be running 2 5508's, WCS and MSE and majority of ap's will be 3502i's. Myself and my coworkers have questions regarding the signal coverage from the internal antenna of these devices. We are planning to mount most of the ap's with internal antenna parallel to the floor as we think that gives the best signal coverage. What are the down falls of mounting a 3502i horizontally towards the "users"? If we have to mount horizontally should we be using the 3502e? This is in a library area, 50 foot ceilings, high density, future voip, mostly concrete and and many bookshelves. Do books cause a lot of signal loss if you have multiple rows of bookshelves? I know the bookshelf itself being made out of metal will cause signal bounce but I wonder about the books. If we put ap's up in monitor mode only, what is the recommendation for number of monitors per number of client accessing ap's?

A. The APs with internal antennas (1130,1140,3502i) have a dome-like coverage, so they are designed for ceiling placement.

Imagine a dome on an AP placed on a wall, perpendicular to floor, the coverage will be awesome on the floor above and below the AP but 20 meters from the AP on a horizontal plane, you'll get nothing. For wall placement, a 3502e with antennas correctly oriented is then better.


The height of your ceiling is a bit of a concern and that means that the coverage on the ground will not be so exciting. However, it would sound like ceiling placement is recommended rather than wall placement since that would mean higher number of obstacles (all the book shelves).


Q12. When you mention "but 20 meters from the AP on a horizontal plane, you'll get nothing" is the 20 meters the maximum distance of the "dome" so to speak? The library has a very high ceiling and we've already recommended no placement on the ceiling. We'll most likely place them in a grid like system on the concrete pillars as cabling and conduit routing are a bit difficult?

A.  The number "20" was a random value. I actually never measured how many meters the coverage goes when the AP is placed on a wall because it's not supposed to :-). I don't know the maximum heigth that people put the AP and still had good coverage


Related Information:-




You can also read the questions he answered during the live event in thisFAQ Document. You can also review theLive Webcast video  and LAB Video with Nicolas gave a presentation on this topic.






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