WiFi Invalid Channel & WiFi inverted on Spectrum Expert

[joeri.de.winter]

Hi everyone,

Since I upgraded my Cisco Spectrum Expert to 4.0.68, I have been detecting some strange type of interference during Spectrum analysis sweeps, the environment were I did those sweeps is not yet active for Wlan clients, so I am not aware if any kind of issues are present on the WLAN.

The interference is defined as WiFi Non Standard

                                                  WiFi Invalid Channel

                                                  WiFi Inverted

Does anybody know what the hack this is....., or were I can find papers on this issue

in the attch you can find a spectrum expert capture....

many thx

greetz

[Kayle Miller]

Check out the 2 links attached, apparently they are new risks that are being scanned for as Clean Air has the option to look for them. Beyond that I can't offer much other insight.

https://supportforums.cisco.com/thread/2107332

http://www.cisco.com/en/US/docs/wireless/controller/7.0/configuration/guide/c70cleanair.pdf

HTH

[joeri.de.winter]

Hey Kayle

thx for the reply, as far as I can understand, it's explained how CleanAir see's this type of interference, 3500 series access points are deployed in the coverage area were I did the spectrum sweep.

the interference sources are classified as

Spectrum 802.11 inverted - A device using spectrally inverted Wi-Fi signals

Spectrum 802.11 non std channel - A device using nonstandard Wi-Fi channels

My questions are:

- does this mean that there are devices active in the area of the spectrum sweep that generate this type of "interference" and needed to be tracked down.

- the real time fft plot shows this signal dwelling on all channels (2.4GHz), how serious should this be interpreted ?

- are these signals generated from the 3500 series?

do not find much info on the net

many thx

jdw

[Kayle Miller]

jdw,

     I agree with you there isn't much about it, and the references I found to it list it being disabled by default. I do have some additional humans that are True gods to spectrum that I am going to ping this off for you.  I'll get back to you later on..

*** UPDATE ***

WiFi inverted-

WiFi is encoded on the physical carrier using I and Q data – this is the relationship between phase, amplitude and frequency -

This link might hurt your head – but it explains what it is -

http://zone.ni.com/devzone/cda/tut/p/id/4805

Spectrally inverted wi-fi is a wi-fi signal with the I and Q reversed – if you have a transmitter and a receiver both expecting this – you have an undetectable bridge – since normal wi-fi chips will see noise.

Wi-Fi invalid channel -

wi-fi that is not operating on a standard channel – like 500 KHz off the center frequency for channel 1.  This is important since the specification allows for a certain amount of Lo (local oscillator) drift and says that you must be able to adjust 250 KHz +/- of center frequency.  But if more than  this in an OFDM rate – it is invisible – or beyond the modulation abilities of the modem.

  This does exist in the wild – we have seen it in wireless audio equipment (sub woofer – using DSSS in 5 GHz not on a known channel – really messed things up)

------------------------------------------------

I hope this helps clarify it, I can't take credit for this information, although it came from a truly knowledgable and trusted source..

HTH

[joeri.de.winter]

Hey Kayle,

thx for the additional info, i did not had the time to do some more research...... hoping to do so in the near future

anyway if you encounter some more info please let me know

many thx

[Kayle Miller]

please rate useful posts.

Thanks

[jgoethals]

I've noticed this "Security-risk Interferer 'WiFi Inverted' is detected by 'AP" in my Cisco Prime Infrastructure. As it seems (seen in this forum https://supportforums.cisco.com/thread/2107332) iPhone's have something to do with it. On the AP where I saw the report one iPhone was connected.