Spectrum intelligence (SI) is a core technology designed to proactively
manage the challenges of a shared wireless spectrum. Essentially, SI brings
advanced interference identification algorithms similar to those used in the
military to the commercial wireless networking world. SI provides visibility to
all the users of the shared spectrum, both Wi-Fi devices and foreign
interferers. For every device that operates in the unlicensed band, SI tells
you: What is it? Where is it? How does it impact the Wi-Fi network? Cisco has
taken the bold step to integrate SI directly into the Wi-Fi silicon and
The integrated solution, referred to as Cisco CleanAir, means that for
the first time WLAN IT manager is able to identify and locate non-802.11
interference sources, which raises the bar on the ease of management and
security of wireless networks. Most importantly, an integrated SI sets the
stage for a new breed of Radio Resource Management (RRM). Unlike previous RRM
solutions that could only understand and adapt to other Wi-Fi devices, SI opens
the path for a second-generation RRM solution that is fully aware of all the
users of the wireless spectrum, and is able to optimize performance in the face
of these varied devices.
The first important point that needs to be made is that from a design
perspective. CleanAir enabled access points (APs) are just that; APs and the
performance is virtually identical to the 1140 APs. Designing for Wi-Fi
coverage is the same with both. CleanAir or interference identification
processes are a passive process. CleanAir is based on the receiver, and for
classification to function, the source needs to be loud enough to be received
at 10 dB above the noise floor. If your network is deployed in such a way that
your clients and APs can hear one another, then CleanAir can hear well enough
to alert you to troubling interference within your network. The coverage
requirements for CleanAir are detailed in this document. There are some special
cases depending on the CleanAir implementation route you ultimately choose. The
technology has been designed to compliment the current best practices in Wi-Fi
deployment. This includes the deployment models of other widely used
technologies such as Adaptive wIPS, Voice, and location deployments.
Cisco recommends that you have knowledge of CAPWAP and Cisco Unified
Wireless Network (CUWN).
The information in this document is based on these software and
CleanAir capable APs are Aironet 3502e, 3501e, 3502i, and
Cisco WLAN Controller (WLC) running version
Cisco Wireless Control System (WCS) running version
Cisco Mobility Services Engine (MSE) running version
Technical Tips Conventions for more information on document
CleanAir is a system, not a feature. CleanAir software and hardware
components provide the ability to accurately measure Wi-Fi Channel quality and
identify non-Wi-Fi sources of channel interference. This cannot be done with a
Standard Wi-Fi chipset. In order to understand design goals and requirements
for successful implementation it is necessary to understand how CleanAir works
at a high level.
For those already familiar with Cisco’s Spectrum Expert technology,
CleanAir is a natural evolutionary step. But, it is a completely new technology
in that this is an enterprise-based distributed spectrum analysis technology.
As such, it is similar to Cisco Spectrum Expert in some respects but very
different in others. The components, functions, and features are discussed in
The new CleanAir capable APs are Aironet 3502e, 3501e, 3502i, and
3501i. The e designates External Antenna, the I designates Internal antenna.
Both are fully functional next generation 802.11n APs and run on standard
Figure 1: C3502E and C3502I CleanAir Capable
The Spectrum Analysis hardware is directly integrated into the chipset
of the radio. This addition added over 500 K logic gates to the radio silicon,
and has provided exceptionally close coupling of the features. There are many
other traditional features, which have been added or improved with these
radios. But, it is beyond the scope of this document and these are not covered
here. Suffice it is to say, that on its own without CleanAir the 3500 series
APs pack a lot of features and performance into an attractive and robust
The basic Cisco CleanAir architecture consists of Cisco CleanAir
enabled APs and a Cisco WLAN controller (WLC). Cisco Wireless Control System
(WCS) and Mobility Services Engine (MSE) are optional system components. In
order to get full value from the information that the CleanAir system supplies,
the WCS and MSE together are key to leveraging a wider efficacy of CleanAir.
This provides user interfaces for advanced spectrum capabilities such as
historic charts, tracking interference devices, location services and impact
An AP equipped with Cisco CleanAir technology collects information
about non-Wi-Fi interference sources, process it and forward to the WLC. The
WLC is an integral core part of the CleanAir system. The WLC controls and
configures CleanAir capable APs, collects and processes spectrum data and
provides it to the WCS and/or the MSE. The WLC provides local user interfaces
(GUI and CLI) to configure basic CleanAir features and services and display
current spectrum information.
The Cisco WCS provides advanced user interfaces for CleanAir that
include feature enabling and configuration, consolidated display information,
historic Air Quality records and reporting engines.
Figure 2: Logical System Flow
The Cisco MSE is required for location and historic tracking of
interference devices, and provides coordination and consolidation of
interference reports across multiple WLCs.
Note: A single WLC can only consolidate interference alerts for APs
directly connected to it. Coordination of reports that come from APs attached
to different controllers requires the MSE which has a system wide view of all
CleanAir APs and WLCs.
The heart of the CleanAir system is the Spectrum Analysis Engine (SAgE)
ASIC, the spectrum analyzer on a chip. However, it is much more than just a
spectrum analyzer. At the core is a powerful 256 point FFT engine which
provides an amazing 78 KHz RBW (Resolution Band Width, the minimum resolution
which can be displayed) purpose built pulse and statistics gathering engines as
well as the DSP Accelerated Vector Engine (DAvE). The SAgE hardware runs in
parallel with the Wi-Fi chipset and processes near line rate information. All
of this allows extreme accuracy and scales for large numbers of like
interference sources, with no penalty in throughput of user traffic.
The Wi-Fi chipset is always on line. SAgE scans are performed once per
second. If a Wi-Fi preamble is detected, it is passed through to the chipset
directly and is not affected by the parallel SAgE hardware. No packets are lost
during SAgE scanning, SAgE is disabled while a Wi-Fi packet is processed
through the receiver. SAgE is very fast and accurate. Even in a busy
environment, there is more than enough scan time to accurately assess the
Why does RBW matter? If you need to count and measure the difference
between several Bluetooth radios hopping with narrow signals at 1600 hops per
second, you need to separate different transmitters hops in your sample if you
want to know how many there are. This takes resolution. Otherwise, it would all
look like one pulse. SAgE does this, and it does this well. Because of the DAvE
and being associated on board memory, the ability to process multiple
samples/interferers in parallel is there. This increases the speed, which
allows you to process the data stream in near real time. Near real time means
there is some delay, but it is so minimal it takes a computer to measure it.
Cisco CleanAir APs produce two basic types of information for the
CleanAir system. An IDR (Interference Device Report) is generated for each
classified interference source. AQI’s (Air Quality Index) reports are generated
every 15 seconds and passed to Cisco IOS® for
averaging and eventual transmission to the controller based on the configured
interval. CleanAir messaging is all handled on the control plane in two new
CAPWAP message types: Spectrum Configuration and Spectrum Data. Formats for
these messages are listed here:
WLC – AP
CAPWAP msg: CAPWAP_CONFIGURATION_UPDATE_REQUEST = 7
payload type: Vendor specific payload type (104 -?)
vendor type: SPECTRUM_MGMT_CFG_REQ_PAYLOAD = 65
Payload type: Vendor specific payload type (104 -?)
vendor types: SPECTRUM_MGMT_CAP_PAYLOAD = 66
SPECTRUM_MGMT_CFG_RSP_PAYLOAD = 79
SPECTRUM_SE_STATUS_PAYLOAD = 88
Spectrum data AP – WLC
CAPWAP: IAPP message
IAPP subtype: 0x16
data type: AQ data – 1
main report 1
worst interference report 2
IDR data – 2
The Interference Device Report (IDR) is a detailed report that contains
information about a classified interference device. This report is very similar
to the information that is seen in Cisco Spectrum Expert Active Devices, or
Devices View. Active IDRs can be viewed on the WLC GUI/and CLI for all CleanAir
radios on that WLC. IDRs are forwarded to the MSE only.
This is the format for an IDR report:
Table 1 - Interference Device Report
The number uniquely identifies interference device for the
specific radio. It consists of upper 4 bits generated during the system boot
and lower 12 bits running number.
device class type
Radio Band ID
1 = 2.4 GHz, 2 = 5 GHz, 4 = 4.9 GHz; 2 MSBs reserved. 4.9GHz is
not supported for initial release.
initial device detection time
Interference Severity Index
1 – 100, 0x0 is reserved for undefined/hidden
Detected on Channels
support for detection on multiple channels within the same
Interference Duty Cycle
1 – 100%
Support for multiple antenna reports is reserved for the future
Tx Power (RSSI) per antenna
Device Signature length
Length of “Device Signature” field. Currently the length could
be in the range 0 - 16 bytes.
Parameter represents either unique device MAC address or device
PMAC signature. See PMAC definition below.
An IDR is produced for each classified device. An individual radio can
track a theoretical infinite number of devices similar to what the Spectrum
Expert card does today. Cisco has tested hundreds with success. However, in an
enterprise deployment there are hundreds of sensors, and a practical reporting
limit is enforced for scaling purposes. For CleanAir APs, the top ten IDRs
based on severity are reported. One exception to this rule is the case of the
security interferer. A security IDR is always given precedence regardless of
severity. The AP tracks which IDRs have been sent to the controller, and adds
or deletes as needed.
Table 2: Example of IDR tracking table on the AP
Note: Interference sources marked as Security Interferers are user
designated and can be configured through Wireless > 802.11a/b/g/n >
cleanair > enable interference for security alarm. Any interference source
that is classified can be chosen for a security trap alert. This sends a
security trap to the WCS or another configured trap receiver based on the type
of interferer selected. This trap does not contain the same information as an
IDR. It is simply a way to trigger an alarm on the presence of the interferer.
When an interferer is designated as a security concern, it is marked as such at
the AP and is always included in the ten devices that are reported from the AP
regardless of severity.
IDR messages are sent in real time. On detection the IDR is marked as
device up. If it stops a device down message is sent. An update message is sent
every 90 seconds from the AP for all devices currently being tracked. This
allows for status updates of tracked interference sources and an audit trail in
the event an up or down message was lost in transit.
Air Quality (AQ) reporting is available from any spectrum capable AP.
Air Quality is a new concept with CleanAir and represents a “goodness” metric
of the available spectrum and indicates the quality of bandwidth available for
the Wi-Fi channel. Air Quality is a rolling average that evaluates the impact
of all classified interference devices against a theoretical perfect spectrum.
The scale is 0-100 % with 100% representing Good. AQ reports are sent
independently for each radio. The latest AQ report is viewable on the WLC GUI
and CLI. AQ reports are stored on the WLC and polled by WCS regular interval.
The default is 15 minutes (minimum) and can be extended to 60 minutes on the
Currently, most standard Wi-Fi chips evaluate the spectrum by tracking
all of the packets/energy that can be demodulated on receive, and all of the
packets/energy that it is transmitting. Any energy that remains in the spectrum
that cannot be demodulated or accounted for by RX/TX activity is lumped into a
category called noise. In reality a lot of the “noise” is actually remnants
from collisions, or Wi-Fi packets that fall below the receive threshold for
With CleanAir, a different approach is taken. All of the energy within
the spectrum that is definitely NOT Wi-Fi is classified and accounted for. We
can also see and understand energy that is 802.11 modulated and classify energy
that is coming from Co-channel and Adjacent channel sources. For each
classified device a severity index is calculated (see the Severity section), a
positive integer between 0 and 100 – with 100 being the most severe.
Interference severity is then subtracted from the AQ scale (starting at 100 –
good) to generate the actual AQ for a channel/radio, AP, Floor, Building or
campus. AQ then is a measurement of the impact of all classified devices on the
There are two AQ reporting modes defined: normal and rapid update.
Normal mode is the default AQ reporting mode. Either the WCS or the WLC
retrieves reports at normal update rate (default is 15 minutes). The WCS
informs the Controller about the default polling period, and the WLC instructs
the AP to change AQ averaging and reporting period accordingly.
When the user drills down to Monitor > Access Points > and
chooses a radio interface from the WCS or the WLC, the selected radio is placed
into rapid update reporting mode. When a request is received, the Controller
instructs the AP to change the default AQ reporting period temporarily to a
fixed fast update rate (30 sec), which allows near real-time visibility into AQ
changes at the radio level.
Default reporting state is “ON”.
Table 3: Air Quality Report
In local mode – this would be the served channel
Lowest AQ detected during the reporting period.
The following parameters are averaged on AP over the reporting
Air Quality Index (AQI)
Total Channel Power (RSSI)
These parameters show total power from all the sources
including both interferers and WiFi devices.
Total Channel Duty Cycle
Interference Power (RSSI)
Interference Duty Cycle
non WiFi devices only
Multiple entries for each detected device is attached to the report,
ordered by device severity. The format for these entries is here:
Table 4: AQ Device Report
device class type
Interference Severity Index
Interference Power (RSSI)
Note: In the context of spectrum reporting, Air Quality represents
interference from non-Wi-Fi sources and Wi-Fi sources not detectable by a Wi-Fi
AP during normal operation (for example, old 802.11 frequency hopper devices,
altered 802.11 devices, Adjacent overlapping Channel Interference, etc).
Information about Wi-Fi based interference is collected and reported on by the
AP using the Wi-Fi chip. A Local mode AP collects AQ information for the
current serving channel(s). A Monitor Mode AP collects information for all
channels configured under scan options. The standard CUWN settings of Country,
DCA, and All channels is supported. When an AQ report is received, the
Controller performs required processing and store it in the AQ database.
As previously mentioned, CleanAir is the integration of Cisco Spectrum
Expert technology within a Cisco AP. While similarities might exist, this is a
fresh use of the technology and many new concepts are presented in this
Cisco Spectrum Expert introduced technology that was able to positively
identify non-Wi-Fi sources of radio energy. This permitted the operator to
focus on information such as duty cycle and operating channels, and make an
informed decision about the device and its' impact on their Wi-Fi network.
Spectrum Expert allowed the operator to then lock the chosen signal into the
device finder application and physically locate the device by walking around
with the instrument.
The design goal of CleanAir is to go several steps further, by
essentially removing the operator further from the equation and automating
several of the tasks within system management. Because you can know what the
device is and what it is affecting, better decisions can be made at a system
level on what to do with the information. Several new algorithms have been
developed to add intelligence to the work that was started with Cisco Spectrum
Expert. There are always cases that require physically disabling an
interference device, or making a decision about a device and impact that
involves humans. The overall system should heal what can be healed and avoid
what can be avoided so that the effort to reclaim affected spectrum can be a
proactive exercise instead of a reactive one.
Local Mode AP (recommended) (LMAP)—A Cisco CleanAir AP
operating in LMAP mode is serving clients on it’s assigned channel. It is also
monitoring the Spectrum on that channel and that channel ONLY. Tight silicon
integration with the Wi-Fi radio allows the CleanAir hardware to listen between
traffic on the channel that is currently being served with absolutely no
penalty to throughput of attached clients. That is line rate detection without
interrupting client traffic.
There are no CleanAir dwells processed during normal off channel scans.
In normal operation, a CUWN Local Mode AP executes an off channel passive scans
of the alternate available channels in 2.4 GHz and 5 GHz. Off channel scans are
used for system maintenance such as RRM metrics and rogue detection. The
frequency of these scans is not sufficient to collect back to back dwells
required for positive device classification, so information gleaned during this
scan is suppressed by the system. Increasing the frequency of off channel scans
is also not desirable, as it takes away from time that the radio services
What does this all mean? A CleanAir AP in LMAP mode only scans one
channel of each band continuously. In normal enterprise densities there should
be plenty of APs on the same channel, and at least one on each channel assuming
RRM is handling channel selection. An interference source that uses narrow band
modulation (operates on or around a single frequency) is only detected by APs
that share that frequency space. If the interference is a frequency hopping
type (uses multiple frequencies – generally covering the whole band) it is
detected by every AP that can hear it operating in the band.
Figure 4: LMAP AP detection example
In 2.4 GHz, LMAPs have sufficient density to generally ensure at least
three points of classification. A minimum of three detection points is required
for location resolution. In 5 GHz, there are 22 channels operating in the
United States, thus detection density and sufficient location density is less
likely. However, if interference is operating on a channel occupied by a
CleanAir AP, it detects it and alert or take steps to mitigate if those
features are enabled. Most interference seen is confined to the 5.8 GHz portion
of the band. This is where consumer devices live and hence where it is most
likely to be encountered. You can limit your channel plan to force more APs to
that space if you desire. However, it is not really warranted. Remember,
interference is only a problem if it is using spectrum you need. If your AP is
not on that channel, it is likely that you still have plenty of spectrum left
to move into. What if the need to monitor all of 5 GHz is driven by security
policies? See the Monitor Mode AP definition below.
Monitor Mode AP (optional) (MMAP)—A CleanAir Monitor
mode AP is dedicated and does not serve client traffic. It provides full time
scanning of all channels using 40 MHz dwells. CleanAir is supported in monitor
mode along with all other current monitor mode applications including Adaptive
wIPS and location enhancement. In a dual radio configuration this ensures that
all bands-channels are routinely scanned.
CleanAir enabled MMAPs can be deployed as part of a pervasive
deployment of CleanAir enabled LMAPs to provide additional coverage in 2.4 and
5 GHz, or as a standalone overlay solution for CleanAir functionality in an
existing non-CleanAir AP deployment. In a scenario as mentioned above where
security is a primary driver, it is likely that Adaptive wIPS would also be a
requirement. This is supported concurrently with CleanAir on the same MMAP.
There are some distinct differences in how some of the features are
supported when deploying as an overlay solution. Thisis covered in the
deployment models discussion in this document.
Spectrum Expert Connect Mode – SE Connect
(optional)—An SE Connect AP is configured as a dedicated Spectrum
Sensor that allows connection of the Cisco Spectrum Expert application running
on a local host to use the CleanAir AP as a remote spectrum sensor for the
local application. The connection between Spectrum Expert and the remote AP
bypasses the controller on the data plane. The AP remains in contact with the
controller on the control plane. This mode allows viewing of the raw spectrum
data such as FFT plots and detailed measurements. All CleanAir system
functionality is suspended while the AP is in this mode, and no clients are
served. This mode is intended for remote troubleshooting only. The Spectrum
Expert application is a MS Windows application that connects to the AP via a
TCP session. It can be supported in VMWare.
In CleanAir the concept of Air Quality was introduced. Air Quality is a
measurement of the percentage of time that the spectrum at a particular
observed container (radio, AP, Band, Floor, Building) is available for Wi-Fi
traffic. AQ is a function of the severity index, which is calculated for each
classified interference source. The Severity index evaluates each non- Wi-Fi
devices over the air characteristics and calculates what percentage of time the
spectrum is not available for Wi-Fi with this device present.
Air Quality is a product of the severity indexes of all classified
interference sources. This is then reported as the overall Air Quality by
radio/channel, band, or RF propagation domain (floor, building) and represents
the total cost against available airtime of all non- Wi-Fi sources. Anything
that is left is theoretically available to the Wi-Fi network for traffic.
This is theoretical because there is a whole science behind measuring
the efficiency of Wi-Fi traffic, and this is beyond the scope of this document.
However, knowing that interference is or is not impacting that science is a key
goal if your plan is success in identifying and mitigating pain points.
What makes an interference source severe? What determines if it is/or
is not a problem? How do I use this information to manage my network? These
questions are discussed in this document.
In the simplest terms, non- Wi-Fi utilization comes down to how often
another radio is using my networks spectrum (Duty Cycle) and how loud is it in
relation to my radios (RSSI/location). Energy in the channel that is seen by an
802.11 interface trying to access the channel is perceived as a busy channel if
it is above a certain energy threshold. This is determined by clear channel
assessment (CCA). Wi-Fi uses a listen before talk channel access method for
contention free PHY access. This is per CSMA-CA (-CA=collision avoidance).
The RSSI of the interferer determines if it can be heard above the CCA
threshold. The Duty Cycle is the on time of a transmitter. This determines how
persistent an energy is in the channel. The higher the duty cycle the more
often the channel is blocked.
Simple severity can be demonstrated this way then using strictly the
RSSI and the Duty Cycle. For illustration purposes, a device with 100% duty
cycle is assumed.
Figure 5: As interference signal decreases - AQI
In the graph in this figure you can see that as the signal power of the
interference decreases, the resulting AQI increases. Technically, as soon as
the signal falls below -65 dBm, the AP no longer is blocked. You do need to
think abut the impact this has on clients in the cell. 100% duty cycle (DC)
ensures constant disruption of client signals with insufficient SNR in the
presence of the noise. AQ rapidly increases once the signal power falls below
So far there are two of the three major impacts of interference defined
in the severity based Air Quality metric:
Interference is straightforward when looking at 100% DC. This is the
type of signal most often used in demonstrations of the affect of interference.
It is easy to see in a spectrogram, and it has a very dramatic affect on the
Wi-Fi channel. This does happen in the real world too, for example in analog
video cameras, motion detectors, telemetry equipment, TDM signals, and older
There are a lot of signals that are not 100% DC. In fact, a lot of the
interference that is encountered is interference of this type: variable to
minimal. Here it gets a bit tougher to call the severity. Examples of
interference of this type are Bluetooth, Cordless Phones, wireless speakers,
telemetry devices, older 802.11fh gear and so on. For instance, a single
Bluetooth headset does not do much damage in a Wi-Fi environment. However,
three of these with overlapping propagation can disconnect a Wi-Fi phone if
In addition to CCA, there are provisions in the 802.11 specifications
such as the contention window, which is needed to accommodate airtime of
different base protocols. Then you add to this various QOS mechanisms. All of
these media reservations are used by different applications to maximize airtime
efficiency and minimize collisions. This can be confusing. However, because all
the interfaces on the air participate and agree on the same group of standards,
it works very well. What occurs to this ordered chaos when you introduce a very
specific energy that does not understand the contention mechanisms or for that
matter does not even participate in CSMA-CA? Well, mayhem actually, to a
greater or lesser degree. It depends how busy the medium is when the
interference is experienced.
Figure 6: Similar but Different Channel Duty
You can have two identical signals in terms of the Duty Cycle as
measured in the channel and amplitude, but have two totally different levels of
interference experienced on a Wi-Fi network. A fast repeating short pulse can
be more devastating to Wi-Fi than a relatively slow repeating fat one. Look at
an RF jammer, which effectively shuts down a Wi-Fi channel and registers very
little duty cycle.
In order to do a proper job evaluating, you need a better understanding
of the minimum interference interval introduced. The minimum interference
interval accounts for the fact that in-channel pulses interrupt Wi-Fi activity
for some period longer than their actual duration, due to three effects:
If already counting down, Wi-Fi devices must wait an additional DIFS
period after the interference pulse. This case is typical for heavily loaded
networks, where the interference starts before the Wi-Fi’s back-off counter has
counted down to zero.
If a new packet arrives to be transmitted mid-interference, the Wi-Fi
device must additionally back off using a random value between zero and CWmin.
This case is typical for lightly loaded networks, where the interference starts
before the Wi-Fi packet arrives to the MAC for transmission.
If the Wi-Fi device is already transmitting a packet when the
interference burst arrives, the whole packet must be retransmitted with the
next-higher value of CW, up to CWmax. This case is typical if the interference
starts second, partially through an existing Wi-Fi
If the back off time expires without a successful retransmission, then
the next back off is double the previous. This continues with unsuccessful
transmission up to CWmax is reached or TTL is exceeded for the frame.
Figure 7 - For 802.11b/g CWmin = 31, for 802.11a CWmin is 15, both
have CWmax of 1023
In a real Wi-Fi network, it is difficult to estimate the mean duration
of these three effects because they are functions of the number of devices in
the BSS, overlapping BSSs, device activity, packet lengths, supported speeds/
protocols, QoS, and present activity. Therefore, the next best thing is to
create a metric that remains constant as a reference point. This is what
Severity does. It measures the impact of a single interferer against a
theoretical network, and maintains a constant report of severity regardless of
the underlying utilization of the network. This gives us a relative point to
look at across network infrastructures.
The answer to the question “how much non- Wi-Fi interference is bad” is
subjective. In lightly loaded networks it is quite possible to have levels of
non- Wi-Fi interference that go unnoticed by the users and administrators. This
is what leads to trouble in the end. The nature of wireless networks is to
become busier over time. Success leads to faster organizational adoption, and
to new applications being committed. If there is interference present from day
one, it is quite likely that the network have a problem with this when it
becomes busy enough. When this happens it is difficult for people to believe
that something that has been fine seemingly all along is the culprit.
How do we use CleanAir’s Air Quality and Severity metrics?
AQ is used to develop and monitor a baseline spectrum measurement and
alert on changes indicating a performance impact. You can also use it for long
term trend assessment through reporting.
Severity is used to evaluate interference impact potential and
prioritize individual devices for mitigation.
Non Wi-Fi transmitters are less than friendly when it comes to unique
characteristics that can be used to identify them. That is essentially what
made the Cisco Spectrum Expert solution so revolutionary. Now with CleanAir
there are multiple APs that potentially all hears the same interference at the
same time. Correlating these reports to isolate unique instances is a challenge
that had to be solved to provide advanced features, such as location of
interference devices, as well as an accurate count.
Enter the Pseudo MAC or PMAC. Because an analog video device does not
have a MAC address or, in several cases, any other identifying digital tag an
algorithm had to be created to identify unique devices being reported from
multiple sources. A PMAC is calculated as part of the device classification and
included in the interference device record (IDR). Each AP generates the PMAC
independently, and while it is not identical for each report (at a minimum the
measured RSSI of the device is likely different at each AP), it is similar. The
function of comparing and evaluating PMACs is called merging. The PMAC is not
exposed on customer interfaces. Only the results of merging are available in
the form of a cluster ID. This merging is discussed next.
Figure 8: Raw Detection of Interference
In this graphic you can see several APs all reporting DECT, such as
Phone energy. However, the APs in this graphic are actually reporting on the
presence of two distinct DECT, such as Phone sources. Before the assignment of
a PMAC and subsequent merging, there is only the device classification, which
can be misleading. PMAC gives us a way to identify individual interference
sources, even if they do not have any logical information that can be used such
as an address.
There are several APs all reporting a similar device. For each
reporting AP, the PMAC is assigned to the classified signal. The next step is
to combine the PMACs that are likely the same source device to a single report
for the system. This is what merging does, consolidating multiple reports to a
Merging uses spatial proximity of the reporting APs. If there are six
similar IDRs with five from APs on the same floor, and another one from a
building a mile away, it is unlikely this is the same interferer. Once a
proximity is established, a probability calculation is run to further match the
distinct IDRs that belong and the result is assigned to a cluster. A cluster
represents the record of that interference device and captures the individual
APs that are reporting on it. Subsequent IDR reports or updates on the same
device follow the same process and instead of creating a new cluster are
matched to an existing one. In a cluster report, one AP is designated as the
Cluster Center. This is the AP that hears the interference the loudest.
Figure 9: After the PMAC Merge - AP's hearing the same physical
device are identified
The merging algorithm runs on every CleanAir enabled WLC. A WLC
performs the merge function for all IDRs from APs that are physically
associated to it. All IDRs and resulting merged clusters are forwarded to an
MSE, if it exists in the system. Systems with more than one WLC require an MSE
to provide merging services. The MSE performs a more advanced merging function
that seeks to merge clusters reported from different WLCs and extract location
information to be reported to the WCS.
Why do we need an MSE to merge IDRs across multiple WLCs? Because a
single WLC only knows the neighbors for the APs physically associated to it. RF
Proximity cannot be determined for IDRs coming from APs located on different
controllers unless you have a full system view. The MSE has this view.
How physical proximity is determined differs, depending on how you
implement CleanAir as well.
For LMAP pervasive implementations, the APs all participate in
Neighbor Discovery, so it is an easy matter to consult the RF neighbor list and
determine spatial relationships for IDRs.
In an MMAP overlay model you do not have this information. MMAPs are
passive devices and do not transmit neighbor messages. Therefore, establishing
the spatial relationship of one MMAP to another MMAP has to be done using X and
Y coordinates from a system map. In order to do this, you also need the MSE
that knows about the system map and can provide merging
More detail on the different modes of operation as well as practical
deployment advice is covered in the deployment models section.
Deploying APs in mixed mode – LMAP CleanAir APs with an overlay of MMAP
CleanAir APs is the best approach to high accuracy and total coverage. You can
use the neighbor list created by the received neighbor messages for the MMAP as
part of the merging information. In other words, if you have a PMAC from a LMAP
AP and a PMAC from a MMAP, and the MMAP shows the LMAP AP as a neighbor, then
the two can be merged with a high degree of confidence. This is not possible
with CleanAir MMAPs deployed within legacy standard APs because those APs do
not produce IDRs to compare with the merge process. The MSE and the X and Y
references are still needed.
Determining the location of a radio transmitter in theory is a fairly
straightforward process. You sample the received signal from multiple locations
and you triangulate based on the received signal strength. On a Wi-Fi network
clients are located and Wi-Fi RFID tags with good results as long as there is a
sufficient density of receivers and adequate signal to noise ratio. Wi-Fi
clients and tags send probes on all supported channels regularly. This ensures
that all APs within range hear the client or TAG regardless of the channel it
is serving. This provides a lot of information to work with. We also know that
the device (tag or client) subscribes to a specification that governs how it
operates. Therefore, you can be certain that the device is using an
omni-directional antenna and has a predictable initial transmit power. Wi-Fi
devices also contain logical information that identifies it as a unique signal
source (MAC address).
Note: There is no guarantee of accuracy for location of non- Wi-Fi devices.
Accuracy can be quite good and useful. However, there are a lot of variables in
the world of consumer electronics and unintentional electrical interference.
Any expectation of accuracy that is derived from current Client or Tag location
accuracy models does not apply to non- Wi-Fi location and CleanAir features.
Non Wi-Fi interference sources pose a special opportunity to get
creative. For instance, what if the signal you are trying to locate is a narrow
video signal (1 MHz) that is only affecting one channel? In 2.4 GHz this
probably works fine because most organizations have sufficient density to
ensure that at least three APs on the same channel will hear it. However, in 5
GHz this is more difficult since most non-Wi-Fi devices only operate in the 5.8
GHz band. If RRM has DCA enabled with country channels, the number of APs
actually assigned in 5.8 GHz declines because its goal is to spread out channel
re-use and make use of open spectrum. This sounds bad, but remember if you are
not detecting it, then it is not interfering with anything. Therefore, is
really not a problem from a standpoint of interference.
This is however an issue if your deployment concerns extend to
security. In order to gain proper coverage you require some MMAP APs in
addition to the LMAP APs to ensure full spectral coverage within the band. If
your only concern is securing the operating space you are using, then you can
also limit the channels available in DCA and force increased density in the
channel ranges you wish to cover.
The RF parameters of non- Wi-Fi devices can and do vary widely. An
estimate has to be made based on the type of device that is being detected. The
starting RSSI of the signal source needs to be known for good accuracy. You can
estimate this based on experience, but if the device has a directional antenna
the calculations will be off. If the device runs on battery power and
experiences voltage sags or peaks as it operates, this will change how the
system sees it. A different manufacturer's implementation of a known product
might not meet the expectations of the system. This will affect the
Fortunately, Cisco has some experience in this area, and non-Wi-Fi
device location actually works quite well. The point that needs to be made is
that the accuracy of a non- Wi-Fi device location has a lot of variables to
consider, accuracy increases with power, duty cycle, and number of channels
hearing the device. This is good news because higher power, higher duty cycle,
devices that impact multiple channels is generally what is considered to be
severe as far as interference to the network goes.
Cisco CleanAir APs, first and foremost, are access points. What this
means is that there is nothing inherently different about deploying these APs
over deploying any other currently shipping AP. What has changed is the
introduction of CleanAir. This is a passive technology that does not impact the
operation of the Wi-Fi network in any way, other than the noted mitigation
strategies of ED-RRM and PDA. These are only available in a Greenfield
installation and configured off by default. This section will deal with the
sensitivity, density and the coverage requirements for good CleanAir
functionality. These are not all that different from other established
technology models such as a Voice, Video, or Location deployment.
Valid deployment models for CleanAir products and feature
Table 5: CleanAir Deployment Models vs Features
Monitoring (RRM, Rogue, WIPS, Location, etc)
Detect and Analyze RF signals
Classify Individual Interference sources with impact
Event Driven channel changes
Persistent Device avoidance
Locate on map with zone of impact
Cisco Spectrum Expert Connect
CleanAir is a passive technology. All it does is hear things. Because
an AP hears a lot farther than it can effectively talk this makes it a simple
task to do a correct design in a Greenfield environment. Understanding how well
CleanAir hears, and how classification and detection works, will give you the
answers you need for any configuration of CleanAir.
CleanAir depends on detection. The detection sensitivity is more
generous than Wi-Fi throughput requirements with a requirement of 10 dB SNR for
all classifiers, and many operable down to 5 dB. In most conceivable
deployments where coverage is pervasive, there should not be any issues in
hearing and detecting interference within the network infrastructure.
How this breaks down is simple. In a network where the average AP power
is at or between 5-11 dBm (power levels 3-5) then a class 3 (1 mW/0 dBm)
Bluetooth device should be detected down to -85 dBm. Raising the noise floor
above this level creates a slight degradation in detection dB for dB. For
design purposes it is worth adding a buffer zone by setting the minimum design
goal to say -80. This will provide sufficient overlap in most conceivable
Note: Bluetooth is a good classifier to design for because it represents
the bottom end power wise in devices you would be looking for. Anything lower
generally does not even register on a Wi-Fi network. It is also handy (and
readily available) to test with because it is a frequency hopper and will be
seen by every AP, regardless of mode or channel in 2.4 GHz.
It is important to understand your interference source. For instance
Bluetooth. Here are multiple flavors of this in the market presently and the
radios and specification have continued to evolve as most technologies do over
time. A Bluetooth headset that you would use for your cell phone is most likely
a class3 or class2 device. This operates on low power and makes ample use of
adaptive power profiles, which extends battery life and reduces interference.
A Bluetooth headset will transmit frequently on paging (Discovery mode)
until associated. Then it will go dormant until needed in order to conserve
power. CleanAir will only detect an active BT transmission. No RF, then nothing
to detect. Therefore, if you are going to test with something, make sure it is
transmitting. Play some music across it, but force it to transmit. Spectrum
Expert Connect is a handy way to verify if something is, or is not transmitting
and will end a lot of potential confusion.
CleanAir was designed to compliment what is largely considered a normal
density implementation. This definition of Normal continues to evolve. For
instance, just five years ago 300 APs on the same system was considered a large
implementation. In a lot of the world – it still is. Numbers of 3,000-5,000 APs
with many hundreds of them sharing direct knowledge through RF propagation are
What is important to understand is:
CleanAir LMAP supports the assigned channel
Band Coverage is implemented by ensuring that channels are
The CleanAir AP can hear very well, and the active cell boundary is
not the limit.
For Location solutions, the RSSI cutoff value is -75
A minimum of three quality measurements is required for Location
In most deployments it is hard to image a coverage area that will not
have at least three APs within ear shot on the same channel in 2.4 GHz. If
there are not, then location resolution suffers. Add a Monitor Mode AP and use
the guidelines. Remember that the location cutoff is -75 dBm corrects this
because an MMAP listens to all channels.
In locations where there is minimal density location resolution is
likely not supported. But, you are protecting the active user channel extremely
well. Also in such an area, you are generally not talking about a lot of space
so locating an interference source does not pose the same problem as a
Deployment considerations come down to planning the network for desired
capacity, and ensuring that you have the correct components and network paths
in place to support CleanAir functions. RF proximity and the importance of RF
Neighbor Relations cannot be understated. Make sure to understand PMAC and the
merging process well. If a network does not have a good RF design, the neighbor
relations is generally affected. This affects CleanAir performance.
If you plan to install CleanAir MMAPs as an overlay to an existing
network there are some limitations you need to keep in mind. CleanAir 7.0
software is supported on all of Cisco's shipping controllers. Each model
controller supports the maximum rated AP capacity with CleanAir LMAPs. There
are limits in the number of MMAPs that can be supported. The maximum number of
MMAPs is a function of memory. The controller must store AQ details for each
monitored channel. An LMAP requires two channels storage of AQ information.
However, an MMAP is passively scanning and the channel data can be 25 channels
per AP. Use the table below for design guidance. Always refer to the current
release documentation for current information by release.
Table 6: MMAP limits on WLCs
Max # of APs
Supported CleanAir MMAPs
Note: The numbers quoted for clusters (merged interference reports) and
device records (individual IDR Reports before merging) are generous and highly
unlikely to be exceeded in even the worst environments.
Suppose you simply want to deploy CleanAir as a sensor network to
monitor and be alerted about non- Wi-Fi interference. How many Monitor Mode APs
(MMAPs) do you need? The answer is generally 1-5 MMAP to LMAP radios. This of
course depends on your coverage model. How much coverage do you get with an
MMAP AP? Quite a bit actually since you are strictly listening. The coverage
area is far greater than if you also had to communicate and transmit.
How about you visualize this on a map (you can use any planning tool
available following a similar procedure as described below)? If you have WCS
and already have the system maps built, then this is an easy exercise. Use the
planning mode in theWCS maps.
Select Monitor > Maps.
Select the map you want to work with.
In the right hand corner of the WCS screen use the radio button to
select Planning Mode, then click go.
Figure 10: WCS Planning mode
Select ADD APs.
Select the AP type. Use the default antenna’s for internal or change
to match your deployment: 1 AP TX Power for both 5 GHz and 2.4 GHz is 1 dBm
–Class3 BT = 1 mW
Select ADD AP at the bottom.
Figure 11: Add AP in WCS planner
Move the AP to place on your map and select apply.
The heat map populates. Choose -80 dBm for the RSSI cutoff at the top
of the map, the map re-draws if this is a
Here is what your CleanAir MMAP covers for 1 dBm out to -80 dBm. These
results show a cell with a radius of 70 feet or 15,000 ft/2 of
Figure 12: Example Coverage of CleanAir MMAP using 1 dBm power and
-80 dBm cutoff for coverage
Note: Keep in mind that this is a predictive analysis. The accuracy of this
analysis depends directly on the accuracy of the maps used to create it. It is
beyond the scope of this document to provide a step by step instruction on how
to edit maps within a WCS.
A good question you want to ask is “are these MMAPs going to be
deployed strictly for CleanAir?” Or, are you going to take advantage of the
many benefits that can be derived from the inclusion of monitoring APs in your
All of these applications work with CleanAir enabled APs. For Adaptive
wIPS, refer to the
Adaptive wIPS Deployment Guide as the coverage recommendation of
Adaptive wIPS are similar, but dependent on your goals and customers needs. For
location services ensure that you review and understand the deployment
requirements for your technology. All of these solutions are complimentary with
CleanAir design goals.
Why should I not mix CleanAir LMAP and Legacy LMAP APs in the same
physical area? This question pertains to this use case:
“I currently have non CleanAir APs deployed (1130,1240, 1250, 1140) in
local mode. I want to add just a few CleanAir APs to increase my
coverage/density. Why can’t I just add some APs and get all the CleanAir
This is not recommended because CleanAir LMAPs only monitor the serving
channel and all CleanAir features rely on measurement density for quality. This
installation would result in indiscriminate coverage of the band. You could
well end up with a channel (or several) that has no CleanAir coverage at all.
However with the base installation, you would be using all of the channels
available. Assuming RRM is in control (recommended) it is entirely possible
that all of the CleanAir APs could be assigned to the same channel in a normal
installation. You spread them out to try to get the best spatial coverage
possible, and that actually increases the odds of this.
You certainly can deploy a few CleanAir APs in with an existing
installation. It is an AP and would function fine from a client and coverage
standpoint. CleanAir functionality would be compromised and there is no way to
really guarantee what the system would or would not tell you regarding your
spectrum. There are far too many options in density and coverage which can be
introduced to predict. What would work?
AQ would be valid for the reporting radio only. This means it is only
relevant for the channel that it is serving, and this could change at any time.
Interference alerts and zone of impact would be valid. However, any
location derived would be suspect. Best to leave that out all together and
assume closest AP resolution.
Mitigation strategies would be ill-advised to operate because most of
the APs in the deployment would not operate the same way.
You would be able to use the AP to look at spectrum from Spectrum
You would also have the option to temporarily switch to monitor mode
at any time in order to perform a full scan of the environment.
While there are some benefits, it is important to understand the
pitfalls and adjust expectations accordingly. It is not recommended, and issues
arising from this type of deployment are not supportable based on this
A better option if your budget does not support adding APs that do not
serve client traffic (MMAP) is to collect enough CleanAir APs to deploy
together in a single area. Any area that can be enclosed on a map area can
contain a Greenfield CleanAir deployment with full feature support. The only
caveat on this would be location. You still need enough density for location.
While it is not advisable to mix legacy APs and CleanAir APs operating
in local mode in the same deployment area, what about running both on the same
WLC? This is perfectly fine. Configurations for CleanAir are only applicable to
APs that support CleanAir.
For instance, in the RRM configuration parameters for both 802.11a/n
and 802.11b/g/n you see both ED-RRM and PDA configurations for RRM. One might
consider that these would be bad if applied to an AP that was not a CleanAir
capable AP. However, even though these features do interact with RRM, they can
only be triggered by a CleanAir event and are tracked to the AP that triggers
them. There is no chance that a non- CleanAir AP has these configurations
applied to them, even though the configuration applies to the whole RF group.
This raises another important point. While CleanAir configurations on a
7.0 or later controller are effective for any CleanAir AP that attaches to that
controller, ED-RRM and PDA are still RRM configurations.
Implementation of CleanAir draws on many of the architecture elements
present within the CUWN. It has been designed to fortify and add functionality
to every system component, and draws on information that is already present top
enhance usability and tightly integrate the features.
This is the overall breakdown classified into license tiers. Notice
that it is not necessary to have a WCS and or the MSE in the system to get good
functionality from the system. The MIBs are available on the controller and are
open to those who wish to integrate these features into an existing management
For a basic CleanAir system, the requirements are a CleanAir AP and a
WLC that runs version 7.0 or later code. This provides both a CLI and the WLC
GUI for customer interface and all CURRENT data is displayed, including
interference sources reported by band and the SE connect feature. Security
Alerts (Interference sources designated as a security concern) are merged
before triggering the SNMP trap. As previously stated though, WLC merging is
limited to the view of just the APs associated to that controller. There is no
historical support of trend analysis supported directly from the WLC
Adding a BASIC WCS and managing the controller adds trending support
for AQ and alarms. You receive historical AQ reporting, threshold alerts
through SNMP, RRM Dashboard support, Security alert support, and many other
benefits including the client troubleshooting tool. What you do not get is
Interference history and location. This is stored in the MSE.
Note: Adding an MSE to the WCS for location requires both a WCS plus
license and Context Aware feature licenses for the MSE.
Adding an MSE and location solution to the network supports the
historical IDR reporting as well as location based functions. In order to add
this to an existing CUWN solution, you require a plus license on the WCS, and
CAS or Context Aware licenses for the location targets.
1 Interferer = 1 CAS license
Interferers are managed through context aware and an interference that
is tracked in the system is the same as a client for purposes of licensing.
There are many options on how to manage these licenses and what they are used
On the WLC configuration you can limit which interference sources are
tracked for location and reporting in the maps by selecting them from the
controller > Wireless > 802.11b/a > CleanAir menu.
Interference devices selected there are reported, and choosing to
ignore them keeps them out of the location system and MSE. This is completely
separate from what is actually happening at the AP. All classifiers are always
detected at the AP level. This determines what isdone with an IDR report. If
you use this to limit reporting, then it is reasonably safe because all energy
is still seen at the AP and is captured in AQ reports. AQ reports break out the
contributing interference sources by category. If you eliminate a category here
to conserve licensing, it is still reported as a contributing factor in AQ and
you are alerted if you exceed a threshold.
Figure 13: WLC CleanAir configuration -
For instance, suppose the network you are installing is in a retail
environment, and the map is cluttered with Bluetooth targets coming from
headsets. You could eliminate this by de-selecting the Bluetooth Link. If at
some time later Bluetooth became a problem, you would see this category rise in
your AQ reporting and could re-enable at will. There is no interface reset
You also have the element manager under the MSE configurations: WCS
> Mobility Services > Your MSE > Context Aware Service >
administration > tracking Parameters.
Figure 14: MSE Context Aware element manager
This gives the user complete control to assess and manage what licenses
are used for and how they are divided among target categories.
Table 7: CleanAir Features matrix by CUWN
Cisco CleanAir Features by Device
Air Quality and Interference by AP/radio on WLC GUI and CLI
AQ Threshold trap (per radio) from WLC
Interference Device trap (per Radio) from WLC
Rapid Update mode with current AQ charts and interferers for
Spectrum Expert Connect mode
Spectrum MIB on WLC, open to 3rd Parties
Network Air Quality
WCS CleanAir Dashboard showing Graphic AQ history for all
AQ history tracking and reports
AQ Heatmap and aggregated AQ (per floor) on WCS floor
Top N devices for AP shown as hover option on WCS floor
CleanAir-enabled WCS RRM Dashboard
CleanAir-enabled WCS Security Dashboard and
CleanAir-enabled WCS Client Troubleshooting
WCS CleanAir Dashboard with Top N devices with
Merging interference devices across APs
Interference device history tracking with
Location of interferers – Zone of Impact
The minimum required configuration for Cisco CleanAir is the Cisco
CleanAir AP, and a WLC which runs version 7.0. With these two components you
can view all of the information provided by CleanAir APs. You also get the
mitigation features available with the addition of CleanAir APs and the
extensions provided through RRM. This information is viewable via the CLI or
the GUI. The focus is on the GUI in this section for brevity.
WLC Air Quality and Interference Reports
On the WLC you can view current AQ and Interference reports from the
GUI menu. In order to view interference reports, there must be interference
active as the report is for current conditions only
Interference Device Report
Select Monitor > Cisco CleanAir > 802.11a/802.11b >
All active interference devices being reported by CleanAir Radios are
listed by Radio/AP reporting. Details include AP Name, Radio Slot ID,
Interference Type, Affected Channels, Detected Time, Severity, Duty Cycle,
RSSI, Device ID and Cluster ID.
Figure 15: Accessing WLC Interference Device
Air Quality Report
Air Quality is reported by Radio/channel. In the example below,
AP0022.bd18.87c0 is in monitor mode and displays AQ for channels 1-11.
Selecting the radio button at the end of any line allows the option of
showing this information in the radio detail screen, which includes all
information gathered by the CleanAir interface.
Figure 16: WLC Interference Device Report
CleanAir Configuration – AQ and Device Traps
CleanAir allows you to determine both the threshold and types of traps
that you receive. Configuration is by band: Wireless > 802.11b/a >
Figure 17: WLC CleanAir configuration
You can enable and disable CleanAir for the entire controller, suppress
the reporting of all interferers, and determine which interferers to report or
ignore. Selecting specific interference devices to ignore is a useful feature.
For instance you might not want to track all Bluetooth headsets because they
are relatively low impact and you have a lot of them. Choosing to ignore these
devices simply prevents it from being reported. The RF that comes from the
devices is still calculated into the total AQ for the spectrum.
Enable/Disable (on by default) the AirQuality trap.
AQI Alarm Threshold (1 to 100). When you set the AirQuality threshold
for traps, this tells the WLC at what level you want to see a trap for
AirQuality. The default threshold is 35, which is extremely high. For testing
purposes setting this value to 85 or 90 proves more practical. In practice, the
threshold is variable so you can tune it for your specific environment.
Enable Interference for Security Alarm. When you add the WLC to a WCS
system, you can select this check box to treat interference device traps as
security Alarm traps. This allows you to select the types of devices that
appear in the WCS alarm summary panel as a security trap.
Do/do not trap device selection allows control over the types of
devices that generates interference/security trap messages.
Lastly, the status of ED-RRM (Event Driven RRM) is displayed.
Configuration for this feature is covered under the Event Driven RRM - EDRRM
section later in this document.
Rapid Update Mode* - CleanAir Detail
Selecting Wireless > Access Points > Radios > 802.11a/b shows
all of the 802.11b or 802.11a radios attached to the WLC.
Selecting the radio button at the end of the line allows you to see
either the radio detail (traditional non CleanAir metrics of utilization, noise
and the like) or CleanAir detail.
Figure 18: Accessing CleanAir Detail
Selecting CleanAir produces a graphic (default) display of all CleanAir
information pertaining to that radio. The information displayed is now in Rapid
Update Mode by default. This means it is being refreshed every 30 seconds from
the AP instead of the 15 minute averaging period displayed in system level
messaging. From top to bottom, all interferers being detected by that radio
along with the interference parameters of Type, Affected Channels, Detection
Time, Severity, Duty Cycle, RSSI, Device ID, and Cluster ID.
Figure 19: CleanAir Radio Detail Page
From this figure, the displayed charts include:
Air Quality by Channel displays the Air Quality for the channel that is
Non Wi-Fi channel utilization shows the utilization that is directly
attributable to the interference device being displayed. In other words, if you
get rid of that device you regain that much spectrum for Wi-Fi applications to
There are two categories that are introduced here under Air Quality
Adjacent Off Channel Interference (AOCI)—This is interference from a
Wi-Fi device that is not on the reporting operating channel, but is overlapping
the channel space. For channel 6, the report would identify interference
attributable to an AP on channels 4, 5, 7, and 8.
Unclassified—This is energy that is not attributable definitively to
Wi-Fi or non- Wi-Fi sources. Fragments, collisions, things of this nature;
frames that are mangled beyond recognition. In CleanAir guesses must not be
Interference power displays the receive power of the interferer at that
AP. The CleanAir Detail page displays information for all monitored channels.
The examples above are from a Monitor Mode (MMAP) AP. A local Mode AP would
show the same detail, but only for the current served channel.
CleanAir Enabled RRM
There are two key Mitigation Features that are present with CleanAir.
Both rely directly on information that can only be gathered by CleanAir.
Event Driven RRM
Event Driven RRM (ED-RRM) is a feature that allows an AP in distress to
bypass normal RRM intervals and immediately change channels. A CleanAir AP is
always monitoring AQ, and reports on this in 15 second intervals. AirQuality is
a better metric than relying on normal Wi-Fi chip noise measurements because
AirQuality only reports on Classified Interference devices. This makes
AirQuality a reliable metric because it is known what is reported is not
because of Wi-Fi energy (and hence not a transient normal spike).
For ED-RRM a channel change only occurs if the Air Quality is
sufficiently impacted. Because Air Quality can only be affected by a classified
known to CleanAir non- Wi-Fi source of interference (or an adjacent overlapping
Wi-Fi channel), the impact is understood:
Crisis means that CCA is blocked. No clients or the AP can use the
Under these conditions RRM would change the channel on the next DCA
pass. However, that could be a few minutes away (up to ten minutes depending on
when the last run was performed), or the user could have changed the default
interval and it could be longer (selected an anchor time and interval for
longer DCA operation). ED-RRM reacts very quickly (30 seconds) so the users
that change with the AP are likely unaware of the crisis that was close. 30 -50
seconds is not long enough to call a help desk. The users that do not are in no
worse shape than they would have been in the first place. In all cases the
interference source was identified and the AP change reason logs that source,
and the users that have poor roaming receives an answer as to why this change
The channel change is not random. It is picked based on device
contention, thus it is an intelligent alternate choice. Once the channel is
changed there is protection against triggering ED-RRM again in a hold down
timer (60 seconds). The event channel is also marked in RRM DCA for the
affected AP to prevent a return to the event channel (3 hours) in the event the
interferer is an intermittent event and DCA does not see it immediately. In all
cases the impact of the channel change is isolated to the affected AP.
Suppose a hacker or someone of ill intent fires up a 2.4 GHz jammer and
all channels are blocked. First off, all the users within the radius are out of
business anyway. However, suppose ED-RRM triggers on the all APs that can see
it. All APs change channels once, then hold for 60 seconds. The condition would
be met again, so another change would fire with the condition still being met
after 60 seconds. There would be no channels left to change to and ED-RRM
activity would stop.
A security alert would fire off on the jammer (default action) and you
would need to provide a location (if with MSE) or nearest detecting AP. ED-RRM
would log a major AQ event for all affected channels. The reason would be RF
jammer. The event would be contained within the effected RF domain and well
Now the next question that is generally asked, "what if the hacker
walks around with the jammer, would that not that cause all the APs to trigger
Sure you are going to trigger ED-RRM channel changes on all the APs
that have ED-RRM enabled. However, as the jammer moves so does its effect and
usability is restored as soon as it moves. It really does not matter because
you have a hacker walking around with a jammer in their hand disconnecting
users everywhere they go. This is a problem in itself. ED-RRM does not compound
that issue. CleanAir on the other hand is also busy alerting, locating, and
providing the location history of where they went and where they are. These are
good things to know in such a case.
Configuration is accessed under Wireless > 802.11a/802.11b
> RRM > DCA > Event Driven RRM.
Figure 20: Event Driven RRM Configuration
Note: Once ED-RRM is triggered on an AP/Channel the AP is prevented from
returning to that channel for three hours. This is to prevent thrashing if the
signal source is intermittent in nature.
Persistent Device Avoidance
Persistent Device Avoidance is another mitigation feature that is only
possible with CleanAir APs. A device that operates periodically, such as a
microwave oven, can introduce destructive levels of interference while it is
operating. However, once it is no longer in use the air goes quiet again.
Devices such as video cameras, outdoor bridge equipment, and microwave ovens
are all examples of a type of device called persistent. These devices can
operate continuously or periodically, but what they all have in common is that
they do not move frequently.
RRM of course sees levels of RF noise on a given channel. If the device
is operating long enough RRM even moves an active AP off the channel that has
interference. However, once the device goes quiet, it is likely that the
original channel presents as the better choice once again. Because each
CleanAir AP is a spectrum sensor the center of the interference source can be
evaluated and located. Also, you can understand which APs are affected by a
device that you know is there, and potentially operates and disrupts the
network when it does. Persistent Device Avoidance allows us to log the
existence of such interference and remember that it is there so you do not
place an AP back on the same channel. Once a Persistent Device has been
identified it is “remembered” for seven days. If it is not seen again then it
is cleared from the system. Each time you see it, the clock starts over.
Note: Persistent Device Avoidance information is remembered at the AP and
Controller. Rebooting either re-sets the value.
Configuration for Persistent Device Avoidance is located at
Wireless > 802.11a/802.11b > RRM > DCA > Avoid
In order to see if a radio has logged a Persistent Device you can view
the status at Wireless > Access Points > Radios > 802.11a/b
Select a radio. At the end of the line click the radio button and
select CleanAir RRM.
Figure 21: CleanAir Persistent Device Avoidance
Spectrum Expert Connect
CleanAir APs can all support the Spectrum Expert connect mode. This
mode places the APs' radios into a dedicated scanning mode that can drive the
Cisco Spectrum Expert application across a network. The Spectrum Expert console
functions as if it had a local Spectrum Expert card installed.
Note: A routable network path must exist between the Spectrum Expert host
and the target AP. Ports 37540 and 37550 must be open to connect. The Protocol
is TCP, and the AP is listening.
Spectrum Expert connect mode is an enhanced monitor mode, and as such
the AP does not serve clients while this mode is enabled. When you initiate the
mode the AP reboots. When it re-joins the controller it is in Spectrum Connect
mode and have generated a session key for use to connect the application. All
that is required is Cisco Spectrum Expert 4.0 or later, and a routable network
path between the application host and the target AP.
In order to initiate the connection, start by changing the mode on from
Wireless > Access Points > All APs.
Figure 22: AP Mode Configuration
Go to AP Mode, and select SE-Connect. Save the configuration. You
receive two warning screens: one advising that SE-connect mode is not a
client-serving mode, the second warning that the AP is rebooted. Once you have
changed the mode and saved the configuration navigate to the Monitor
> Access Points screen. Monitor the AP status and reload.
Once the AP rejoins and reloads navigate back to the AP configuration
screen, you need the NSI Key for the session that is displayed there. You can
copy and paste the NSI key for the inclusion in launching Spectrum Expert.
Figure 23: NSI Key generated
You need Cisco Spectrum Expert 4.0. Once installed, launch Spectrum
Expert. On the initial splash screen you see a new option, Remote Sensor.
Select Remote Sensor and paste in the NSI Key, and tell Spectrum Expert the IP
address of the AP. Select which radio you wish to connect to and click
Figure 24: Cisco Spectrum Expert Sensor connect
When you add a WCS to the feature mix you get more display options for
CleanAir information. The WLC can display current information, but with WCS the
ability to track, monitor, alert, and report historical AirQuality levels for
all CleanAir APs is added. Also, the ability to correlate CleanAir information
to other award winning dashboards within WCS allows the user to fully
understand their spectrum like never before.
WCS CleanAir Dashboard
The home page has several elements added and is customizable by the
user. Any of the elements displayed on the home page can be re-arranged to user
preferences. That is beyond the scope of this discussion, but keep it in mind
as you use the system. What is being presented here is simply the default view.
Selecting the CleanAir tab takes you to the CleanAir information available on
Figure 25: WCS Home Page
Note: The default settings for the page include a top 10 interferers report
by band in the right hand corner. If you do not have an MSE, this report does
not populate. You can edit this page and add or delete components to customize
it to your liking.
Figure 26: WCS CleanAir Dashboard
Charts displayed on this page display the running historical averages
and minimums for CleanAir spectrum events. The average AQ number is for the
entire system as displayed here. The minimum AQ chart for example tracks, by
band, the minimum reported AQ received from any specific radio on the system in
any 15 minute reporting period. You can use the charts to quickly identify
Figure 27: Minimum Air Quality history chart
Selecting the Enlarge Chart button on the bottom right in any chart
object produces a pop-up window with an enlarged view of the chart in question.
A mouse hover in any chart produces a time and date stamp, and AQ level seen
for the reporting period.
Figure 28: Enlarged Minimum Air Quality
Knowledge of the date and time gives you the information that you need
to search for the particular event, and gather additional details such as APs
that registered the event and device types operating at that time.
AQ threshold alarms are reported to the WCS as performance alarms. You
can also view them through the Alarm Summary panel at the top of the home page.
Figure 29: Alarm Summary panel
Either Advanced Search or simply selecting performance category from
the alarm summary panel (provided you have a performance alarm) yields a list
of performance alarms that contain details about a particular AQ event that is
below the configured threshold.
Figure 30: Air Quality Threshold Alarms
Selecting a particular event displays the detail related to that event
including the date, time, and most importantly the reporting
Figure 31: Performance Alarm Detail
Configurations for Air Quality Thresholds is located under Configure
> Controller, either from the WCS GUI or the Controller GUI. This can be
used for all CleanAir Configurations. The best practice is to use the WCS once
you have assigned a controller to it.
In order to generate performance alarms, you can set the AQ threshold
for a low threshold such as 90 or even 95 (remember that AQ is good at 100 and
bad at 0). You need some interference to trigger it such as a microwave oven.
Remember to put a cup of water in it first and run it for 3-5 minutes.
Air Quality History Tracking Reports
AirQuality is tracked on each CleanAir AP at the radio level. The WCS
enables historical reports for monitoring and trending AQ in your
infrastructure. Reports can be accessed by navigating to the report launchpad.
Select Reports > Report Launchpad.
CleanAir reports are at the top of the list. You can choose to look at
Air Quality vs Time or Worst Air Quality APs. Both reports should be useful in
tracking how Air Quality changes over time and identifying areas that require
Figure 32: Report Launchpad
CleanAir Maps – Monitor > Maps
Selecting Monitor > Maps displays the maps
configured for the system. Average and minimum AQ numbers are presented in
hierarchical fashion corresponding to the container levels of campus, building,
and floor. For instance, at the building level the Average/Minimum AQ is the
average of all CleanAir APs contained in the building. The minimum is the
lowest AQ reported by any single CleanAir AP. Looking at a floor level, the
average AQ represents the average of all APs located on that floor and the
minimum AQ is that of the single worst AQ from an AP on that
Figure 33: Maps main page - showing Air Quality
Selecting a map for a given floor provides detail relevant to the
selected floor. There are a lot of ways that you can view the information on
the map. For instance, you can change the AP tags to display CleanAir
information such as CleanAir Status (shows which APs are capable), minimum or
average AQ values, or Average and Minimum values. The values are relevant to
the band selected.
Figure 34: AP Tags show lots of CleanAir
You can see the interferers that are being reported by each AP in
several ways. Hover over the AP, select a radio, and select the show
interferer’s hotlink. This produces a list of all Interference detected on that
Figure 35: Viewing Interference Devices detected on an
Another interesting way to visualize the impact of interference on the
map is to select the interference tag. Without the MSE, you cannot locate
interference on the map. However, you can select show interference labels,
which are labels with the interferers currently being detected is applied to
all CleanAir radios. You can customize this to limit the number of interferers
displayed. Selecting the hotlink in the tab allows you to zoom in to the
individual interferer details, and all interferers are displayed.
Note: CleanAir APs can track unlimited numbers of interferers. They only
report on the top 10 ordered by severity, with preference being given to a
Figure 36: Interference Tag being displayed on all CleanAir
A useful way to visualize non- Wi-Fi interference and it’s effect is to
view AQ as a heatmap on the map display. Do this by selecting heatmaps and
selecting Air Quality. You can display the average or the minimum AQ. The map
is rendered using the coverage patterns for each AP. Notice that the upper
right corner of the map is white. No AQ is rendered there because the AP is in
monitor mode and passive.
Figure 37: Air Quality Heat Map
CleanAir Enabled RRM Dashboard
CleanAir allows you to see what is in our spectrum that is non- Wi-Fi.
In other words, all those things that were considered just noise can now be
broken down to understand if and how it is impacting your data network. RRM can
and does mitigate noise by selecting a better channel. When this occurs the
solution is generally better than it was, but you are still letting something
that is not your data network occupy your spectrum. This reduces the overall
spectrum available to your data and voice applications.
Wired and Wireless networks differ in that on a wired network if you
need more bandwidth you can install more switches, or ports, or Internet
connections. The signals are all contained within the wire and do not interfere
with one another. In a wireless network, however, there is a finite amount of
spectrum available. Once used, you cannot simply add more.
The CleanAir RRM Dashboard on the WCS allows you to understand what is
going on in your spectrum by tracking non- Wi-Fi interference as well as Signal
from our network, Interference from foreign networks and balancing all within
the spectrum that is available. The solutions that RRM provides do not always
seem optimal. However, there is often something that you cannot see which
causes two APs to operate on the same channel.
The RRM Dashboard is what we use to track events that affect the
balance of spectrum and provide answers as to why something is the way it is.
CleanAir information being integrated to this dashboard is a big step forward
to total control of the spectrum.
Figure 38: CleanAir RRM Channel Change reasons from RRM
Channel Change reasons now include several new categories which refine
the old Noise category (anything that is not Wi-Fi is recognized as noise by
Cisco and all other competitors):
Noise (CleanAir) represents non- Wi-Fi energy in the spectrum as
being a cause or a major contributor to a channel change.
Persistent Non-WiFi interference indicates that a persistent
interferer has been detected and logged on an AP, and the AP changed channels
to avoid this interference.
Major Air Quality Event is the reason for a channel change invoked by
the Event Driven RRM feature.
Other – there is always energy present in the spectrum that is not
demodulated as Wi-Fi, and cannot be classified as a known interference source.
The reasons for this are many: the signals are too corrupted to separate, left
over remnants from collisions is one
Knowing that non-WiFi interference is affecting your network is a big
advantage. Having your network know and act on this information is a big plus.
Some interference you are able to mitigate and remove, some you do not (in the
case of a neighbor's emissions). Typically most organizations have interference
at one level or another, and a lot of this interference is low level enough to
not pose any real problems. However, the busier your network gets the more it
needs an unaffected spectrum.
CleanAir Enabled Security Dashboard
Non-Wi-Fi devices can offer quite a challenge to wireless security.
Having the ability to examine signals at the physical layer allows for much
more granular security. Normal every day consumer wireless devices can and do
bypass normal Wi-Fi security. Because all existing WIDs/WIPs applications rely
on Wi-Fi chipsets for detection, there has been no way to accurately identify
these threats until now.
For instance, it is possible to invert the data in a wireless signal so
that it is 180 degrees out of phase from a normal Wi-Fi signal. Or, you could
change the center frequency of the channel by a few kHz and as long as you had
a client set to the same center frequency you would have a private channel that
no other Wi-Fi chip could see or understand. All that is required is access to
the HAL layer (many are available under GPL) for the chip and a little bit of
skill. CleanAir is able to detect and understand what these signals are. In
addition, CleanAir can detect and locate a PhyDOS attack such as RF Jamming.
You can configure CleanAir to report any device that is classified as a
security threat. This allows the user to determine what should and should not
be transmitting within their facility. There are three ways to view these
events. The most convenient is through the Alarm Summary panel located at the
top of the WCS home page.
A more detailed analysis can be gained by using the Security Dashboard
tab on the main page. This is where all security related information on the
system is displayed. CleanAir now has it’s own section within this dashboard
allowing you to gain a full understanding of the security of your network from
all wireless sources.
Figure 39: Security Dashboard with CleanAr
No matter where you view this information from, you have the detecting
AP, the time and date of the event, and the current status to work with. With
an MSE added you can run periodic reports on just CleanAir security events. Or,
you can look at the location on the map and see the history of the event, even
if it was moving.
CleanAir enabled Client Troubleshooting
The client dashboard on the WCS home page is the one stop for all
things for clients. Because interference often affects a client before it
affects the AP (lower power, poorer antennas) a key thing to know when
troubleshooting client performance issues is if non- Wi-Fi interference is a
factor. CleanAir has been integrated to the Client Troubleshooting tool on the
WCS for that reason.
Access the client information in any way you choose from the dashboard,
either by searching on a MAC address or user. Once you have the client
displayed, select the Client Troubleshooting tool Icon to launch the Client
Figure 40: Client Troubleshooting Dashboard - with
The client tools provide a wealth of information about the client’s
status on the network. Select the CleanAir tab on the Monitor Client screen. If
the AP that the client is currently associated to is reporting any
interference, it is displayed here.
Figure 41: CleanAir tab from Client Troubleshooting
In this case, the interference being detected is a DECT like phone, and
because the severity is only 1 (very low) it would be unlikely to cause a lot
of trouble. However, a couple of Severity 1 devices can cause issues for a
client. The Client Dashboard allows you to quickly rule out, as well as prove,
issues in a logical fashion.
The MSE adds a significant amount of information to CleanAir features.
The MSE is responsible for all location calculations, which are much more
intensive for non-Wi-Fi interference than for a Wi-Fi target. The reason for
this is the range of conditions that location has to work with. There are a lot
of non-Wi-Fi interferers in the world, and they all operate differently. Even
among similar devices there can be great differences in signal strength or
The MSE is also who manages merging of devices that span multiple
controllers. If you recall, a WLC can merge devices that APs reports, which it
is managing. But, interference can be detected that is present on APs that are
not all on the same controller.
All of the features that MSE enhances are located only in the WCS. Once
you have located an interference device on a map, there are several things that
can be calculated and presented about how that interference interacts with your
WCS CleanAir Dashboard with MSE
Previously in this document, the CleanAir Dashboard and how the top 10
interferers per band would not be displayed without the MSE was discussed. With
the MSE, these are now active because you have the interference device and
location information from the MSE’s contribution.
Figure 42: MSE enabled CleanAir dashboard
The upper right hand tables are now populated with the 10 most severe
interference sources detected for each band: 802.11a/n and
Figure 43: Worst Interference for 802.11a/n
The information displayed is similar to that of the interference report
from a specific AP.
Interference ID – this is the database record for the interference on
Type – the type of interferer being detected
Status – currently only displays Active interferers
Severity – the severity calculated for the device
Affected Channels – the channels that the device is being seen
affecting Discovered /last updated time stamps
Floor – the map location of the
If you choose the floor location, it hotlinks you to the map display of
the interference source directly where much more information is
Note: There is one other difference beyond having a location between
information displayed about interferers over what you can see on the AP radio
level directly. You might have noticed that there is no RSSI value for the
interference. This is because the record as seen here is merged. It is the
result of multiple APs reporting the device. The RSSI information is no longer
relevant, nor would it be correct to display it because each AP sees the device
at different signal strength.
WCS Maps with CleanAir device location
Choose the link at the end of the record in order to navigate directly
to the map location of the interference device from the CleanAir
Figure 44: Interference located on the map
Now locating the interference source on the map allows us to understand
its relationship to everything else on the map. In order to product specific
information about the device itself (see figure 36), pass a mouse over the
interference Icon. Notice the detecting APs, this is the list of APs that
currently hears this device. The cluster Center is the AP that is closest to
the device. The last line shows the Zone of Impact. This is the radius that the
interference device would be suspected of being disruptive.
Figure 45: Interference Detail from Mouse
The Zone of Impact is only half the story though. It is important to
remember that a device might have a long reach or large zone of impact.
However, if the severity is low it might or might not matter at all. Zone of
impact can be viewed on the map by selecting Interferers > Zone of Impact
from the map display menu.
Now you can see the Zone of Impact (ZOI) on the map. ZOI is rendered as
a circle around the detected device, and its opacity darkens with higher
severity. This aids visualizing the impact of interference devices greatly. A
small dark circle is much more of a concern than a large translucent circle.
You can combine this information with any other map display or element that you
Double-clicking on any interference icon takes you to the detail record
for that interference.
Figure 46: MSE Interference Record
Interferer details include a lot of information about the type of
interferer that is being detected. In the upper right hand corner is the help
field which tells about what this device is and how this particular type of
device affects your network.
Figure 47: Detailed Help
Other workflow links within the detail record include:
Show Interferers of this Type – links to a filter to show other
instances of this type of device
Show Interferers affecting this band – links to a filtered display of
all same band interferers
Floor – links back to the map location for this
MSE – links to the reporting MSE configuration
Clustered by – links to the controllers that performed the initial
Detecting APs – hot links to the reporting APs for use in viewing the
interference directly from the AP details
Interference Location History
From the command window in the upper right corner of the record display
you can select to view the location history of this interference
Location History shows the position and all relevant data such as
time/date and detecting APs of an interference device. This can be extremely
useful in understanding where the interference has been detected and how it has
behaved or impacted your network. This information is part of the permanent
record of the interference in the MSE database.
WCS – Monitor Interference
The contents of the MSE interferer database can be viewed directly from
the WCS by selecting Monitor > Interference.
Figure 48: Monitor Interferers display
The list is sorted by status by default. However, it can be sorted by
any of the columns contained. You might notice that RSSI information on the
interferer is missing. This is because these are merged records. Multiple APs
hear a particular interference source. All of them hear it differently, so
severity replaces RSSI. You can select any interference IDs in this list to
display the same detailed record as was discussed above. Selecting the device
type produces the help information that is contained within the record.
Selecting the floor location takes you to the map location of the interference.
You can select Advanced Search and query the Interferers database
directly, then filter the results by multiple criteria.
Figure 49: Advance Interference Search
You can choose all interferers by ID, by Type (includes all
classifiers), severity (range), Duty Cycle (range) or location (floor). You can
select the time period, the status (Active/Inactive), select a specific band or
even a channel. Save the search for future use if you like.
There are two basic types of information generated by the CleanAir
components within the system: Interference Device Reports and AirQuality. The
controller maintains the AQ database for all attached radios and is responsible
for generating threshold traps based on the user's configurable thresholds. The
MSE manages Interference Device Reports and merges multiple reports arriving
from controllers and APs that span controllers into a single event, and locates
within the infrastructure. The WCS displays information collected and processed
by different components within the CUWN CleanAir system. Individual information
elements can be viewed from the individual components as raw data, and the WCS
is used to consolidate and display a system wide view and provide automation
and work flow.
CleanAir installation is a straightforward process. Here are some tips
on how to validate the functionality for an initial installation. If you
upgrade a current system or install a new system, the best order of operations
to follow is Controller code, WCS code, then add MSE code to the mix.
Validation at each stage is recommended.
In order to enable CleanAir functionality in the system, you first need
to enable this on the controller through Wireless > 802.11a/b >
Ensure CleanAir is enabled. This is disabled by default.
Once enabled it takes 15 minutes for normal system propagation of Air
Quality information because the default reporting interval is 15 minutes.
However, you can see the results instantly at the CleanAir detail level on the
Monitor > Access Points > 802.11a/n or 802.11b/n
This displays all radios for a given band. CleanAir status is displayed
in the CleanAir Admin Status and CleanAir Oper
Admin Status relates to the radio status for CleanAir – should be
enabled by default
Oper Status relates to the state of CleanAir for the system – this is
what the enable command on the controller menu mentioned above
The operational status cannot be up if the admin status for the radio
is disabled. Assuming that you have an Enable for Admin Status, and Up for
Operational Status, you can select to view the CleanAir details for a given
radio using the radio button located at the end of the row. The selection of
CleanAir for details places the radio into Rapid Update mode and provides
instant (30 second) updates to Air Quality. If you get Air Quality then
You might or might not see interferers at this point. This depends if
you have any active.
As previously mentioned, you do not have Air Quality reports for up to
15 minutes displaying in the WCS > CleanAir tab after initially enabling
CleanAir. However, Air Quality reporting should be enabled by default and can
be used to validate the installation at this point. In the CleanAir tab you do
not have interferers reported in the worst 802.11a/b categories without an MSE.
You can test an individually interference trap by designating an
interference source that you can easily demonstrate as a security threat in the
CleanAir configuration dialogue: Configure > controllers > 802.11a/b >
Figure 50: CleanAir configuration - Security
Adding an interference source for a Security Alarm causes the
controller to send a trap message on discovery. This is reflected in the
CleanAir tab under the Recent Security-risk Interferers
Without the MSE present you do not have any functionality for Monitor
> Interference. This is driven purely by the MSE.
There is nothing particularly special about adding an MSE to the CUWN
for CleanAir support. Once added, there are some specific configurations you
need to make. Ensure that you have synchronized both the system maps and
controller before you enable CleanAir tracking parameters.
On the WCS console, choose Services > Mobility Services >
select your MSE > Context Aware Service > Administration > Tracking
Choose Interferers to enable MSE interference tracking
and reporting. Remember to save.
Figure 51: MSE Context Aware interference
While in the Context Aware Services Administration menu, also visit
History Parameters and enable Interferers here as well. Save your
Figure 52: Context Aware History Tracking
Enabling these configurations signals the synchronized controller to
start the flow of CleanAir IDR information to the MSE and initiates the MSE
tracking and convergence processes. It is possible to get the MSE and a
controller out of synchronization from a CleanAir perspective. This can happen
during an upgrade of controller code when interference sources from multiple
controllers might get bounced (deactivated, and re-activated). Simply disabling
these configurations and re-enabling with a save forces the MSE to re-register
with all synchronized WLCs. Then, the WLCs send fresh data to the MSE,
effectively re-starting the processes of merging and tracking of interference
When you first add an MSE, you must synchronize the MSE with the
network designs and WLCs that you wish for it to provide services for.
Synchronization is heavily dependent on Time. You can validate synchronization
and NMSP protocol functionality by going to Services > Synchronization
services > Controllers.
Figure 53: Controller - MSE Synchronization
You see the sync status for each WLC you are synchronized with. A
particularly useful tool is located under the MSE column heading [NMSP
Selecting this tool provides a wealth of information about the state of
the NMSP protocol, and can give you information on why a particular
synchronization is not occurring.
Figure 54: NMSP Protocol Status
One of the more common issues experienced is that the time on the MSE
and WLC are not the same. If this is the condition, it is displayed in this
status screen. There are two cases:
WLC Time is after the MSE time—This synchronizes. But, there are
potential errors when merging multiple WLCs information.
WLC time is before the MSE time—This does not allow synchronization
because the events have not occurred yet according to the MSE’s
A good practice is to use NTP services for all controllers and the MSE.
Once you have the MSE synchronized and CleanAir enabled, you should be
able to see Interference sources in the CleanAir tab under Worst 802.11a/b
interferers. You can also view them under Monitor > Interference, which is a
direct display of the MSE interference database.
One last potential gotcha exists on the Monitor Interferers display.
The initial page is filtered to only display interferers that have a severity
greater than 5.
Figure 55: WCS - Monitor Interferers display
This is stated on the initial screen, but often goes overlooked when
initializing and validating a new system. You can edit this to display all
interference sources by simply making the severity value 0.
There are many terms used in this document that are not familiar to a
lot of users. Several of these terms come from Spectrum Analysis, some are
Resolution Band Width (RBW), the minimum RBW—The minimum band width
that can be accurately displayed. SAgE2 cards (including the 3500) all have 156
KHz minimum RBW on a 20 MHz dwell, and 78 KHz on a 40 MHz
Dwell–A dwell is the amount of time the receiver spends listening to
a particular frequency. All lightweight access points (LAPs) do off channel
dwell’s in support of rogue detection and metrics gathering for RRM. Spectrum
Analyzers do a series of dwells to cover a whole band with a receiver that only
covers a portion of the band.
DSP—Digital Signal Processing
SAgE—Spectrum Analysis Engine
Duty Cycle—Duty Cycle is the active on time of a transmitter. If a
transmitter is actively using a particular frequency, the only way another
transmitter can use that frequency is to be louder than the first, and
significantly louder at that. A SNR margin is needed to understand it.
Fast Fourier Transform (FFT)—For those interested in the math, google
this. Essentially, FFT is used to quantify an analog signal and convert the
output from the Time domain to the Frequency