802.11b Headers

Hi Guys,

First of all, thanks for all the help you have been giving me, it was
really
helpful for me to understand the USRP / GNU Radio package.

I’m hoping someone from the BBN group is reading this, or anyone else
who
has an idea.
Within our research group we are interested in decoding 11b/(g?) packet
headers. I have installed the 802.11 BBN code, which runs really good.
Even
when I compare it to my laptop, equipped with a packet sniffer, the
detected
packets match perfectly. However, the code decodes packets with a data
rate
of 1Mbit and occasionally a 2Mbit packets due to the USB limitations. We
would like to detect “all” packets, at least their headers containing
the
useful information. Header files use a low modulation type, so I think
we
should always be able to capture the header of a packet. Does anyone see
any
difficulties in doing so?

Any comments are really useful.

Thanks again,

Teun

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Hello Teun,
There are two rates for the 802.11b physical headers - 1 Mbps, and 2
Mbps. Most likely, packets that use the CCK modulation (5.5 and 11
Mbps)
use the 2 Mbps physical header. I never got the 2 Mbps header decoding
working properly for some reason, although the code does try to decode 2
Mbps headers. (It could detect that a 2 Mbps header was there, and
often
got some of the bits correct…) By the way, these headers don’t really
contain that much more information than the packet length and the data
rate

  • however if you want to debug this, I can point you to the appropriate
    places in the code.

    -Dan

Hi Dan,

thanks for your quick reply. The information i’m looking for is exactly
the
packet length and the data rate of a packet. I’m using this information
to
do some sort of wireless environment characterization.

If you can point me to the right places in the code, that would be
awesome.

Thanks,

Teun

Daniel Sumorok wrote:

  • however if you want to debug this, I can point you to the appropriate
    places in the code.

    -Dan

At 05:51 AM 6/29/2007, Teun wrote:

Hi Guys,

First of all, thanks for all the help you have been giving me, it was
really

helpful for me to understand the USRP / GNU Radio package.

I’m hoping someone from the BBN group is reading this, or anyone else who
has an idea.
Within our research group we are interested in decoding 11b/(g?) packet
headers. I have installed the 802.11 BBN code, which runs really good.
Even

when I compare it to my laptop, equipped with a packet sniffer, the
detected

packets match perfectly. However, the code decodes packets with a data
rate

of 1Mbit and occasionally a 2Mbit packets due to the USB limitations. We
would like to detect “all” packets, at least their headers containing the
useful information. Header files use a low modulation type, so I think we
should always be able to capture the header of a packet. Does anyone see
any

http://www.nabble.com/802.11b-Headers-tf3999092.html#a11357744


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http://www.nabble.com/802.11b-Headers-tf3999092.html#a11363044
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