I was sniffing the in air with my Alfa card. I captured few packets with channel ids > 100. I did not get time to look at the packets. But is it possible to have channel id > 100. What I know is channel id is in between 1-14. How it can be 100+ ? Is it possible?
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The most commonly-utilized specifications for wireless LANs (802.11a/b/g/n) use one or two different "bands" of the RF spectrum at the physical layer. 802.11a uses 5 GHz exclusively. 802.11b and 802.11g use 2.4 GHz exclusively. 802.11n is capable of using either.
In the world of 802.11b/g, and 802.11n on 2.4 GHz, the most common channels you'll find in use are 1-11. These are the channels which are legal for non-licensed, low-power usage worldwide. Use of channels above 11 is illegal within the United States. Amateur Radio operators in the United States can run higher-powered transmitters on channels 1-8, although they are subject to some significant restrictions* when doing so. Also, according to Wikipedia, channel 14 is not allowed in "Most of [the] world" with the notable exception of Japan.
One of the primary benefits of the 5 GHz band, which is used by 802.11a and 802.11n, is that there are a lot more channels to choose from and it is therefore much easier to avoid interfering with nearby networks. The channels in this band range (though not quite incrementally or in order) from 7-196.
Legal 5 GHz channels within the United States are 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 136, 140, 149, 153, 157, 161, 165. U.S. licensed Amateur Radio operators may also use channels from 132-165 at higher power, but again are subject to strict regulations* when doing so.
Just as there are many more channels within 5 GHz, regulation of these channels also varies more widely around the world. Wikipedia has a good chart, covering several countries. However, I do not see India on the list - perhaps someone more familiar with their laws can post a local reference.
It should be noted that, while some RF bands may have similarly-numbered channels, transceivers operating on one channel of one band will neither interfere with, nor receive signals from the same numeric channel on another band. For example, if you have an 802.11n 2.4 GHz-only adapter (as is common in most cheap 802.11n devices today), it is physically incapable of using the channels 7-12 on 5 GHz no matter what your locale.
*Restrictions for Amateur Radio operators using these frequencies outside of Part 15 regulations include, but are not limited to station identification, public access, and no use of steganography or cryptography.
does your card support 5GHz spectrum channels? If so it could be that (There's a list of the channel numbers for different parts of the spectrum here)