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.
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.
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.
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.
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?
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 188.8.131.52 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.
A. 1) For everyone, the "M-drive" marketing term englobes the following :
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.
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.
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 Cisco.com:
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).
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