Beacon frames of BBN 802.11

GNU Radio
1

Hi all,
Â
I ran bbn_80211b_rx.py and got the information as follows:
PKT: len=163, rssi=-18, src=00:15:aa:55:6C:82, time=13720, rate=1 Mbps
PKT: len=163, rssi=-23, src=00:15:aa:55:6C:D2, time=21272, rate=1 Mbps
…
Â
Â
According to the information of packets, I don’t think I can know if
these packets are beacon frames or not because I don’t know the subtype
of the frame. However, on the [Discuss-gnuradio] 802.11 on USRP+GNURadio
: “Looking at the archives, I understand that I can receive 1 MbpsÂ
probe/beacon packets with code developed by BBN”, it seems I can know if
the packets are beacon frames. Can anyone tell me how to know if these
packets are beacon frames if it is possible? Thank you!
Â
Jane

2

Thank you for your reply! I ran the ./bbn_80211b_tap.py and then IÂ
used Ctrl-CÂ to stop the bbn_80211b_tap.py. Â After that IÂ ran
./bbn_80211b_tap.py again. However, I got the error as follows:

bbn_tap: created tap device gr1
usrp_open_interface:usb_claim_interface: failed interface 1
could not claim interface 1: Device or resource busy
usrp_basic_tx: can’t open tx interface
Traceback (most recent call last):
 File “./bbn_80211b_tap.py”, line 137, in
   main ()
 File “./bbn_80211b_tap.py”, line 127, in main
   app = app_flow_graph(mac.rx_callback, options)
 File “./bbn_80211b_tap.py”, line 63, in init
   options.barker)
 File
“/usr/local/src/BBN_02192009/adroitgrdevel/gr-bbn/src/examples/bbn_80211b_transmit_path.py”,
line 40, in init
   self.u = usrp.sink_c()
 File “/usr/local/lib/python2.5/site-packages/gnuradio/usrp.py”, line
214, in init
   fpga_filename, firmware_filename)
 File “/usr/local/lib/python2.5/site-packages/gnuradio/usrp1.py”, line
710, in sink_c
   return _usrp1.sink_c(*args)
RuntimeError: can’t open usrp1
bbn_tap: destroying tap device gr1

I guess that I did not stop the ./bbn_80211b_tap.py correctly at the
first time. What should I do to avoid this kind of error?

Thank you,
Jane

From: Doug G. [email protected]
To: Jane C. [email protected]
Cc: [email protected]
Sent: Saturday, February 21, 2009 8:52:34 AM
Subject: Re: [Discuss-gnuradio] Beacon frames of BBN 802.11

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Jane C. wrote:

…
if the packets are beacon frames. Can anyone tell me how to know if
these packets are beacon frames if it is possible? Thank you!

Â

Jane

The BBN 802.11 code can currently only deal with 1 and 2Mbps packets
(i.e. using either DBPSK or DQPSK modulation and DSSS with length-11
Barker Code). Since most WiFi traffic these days tends to be at higher
data rates (unless the client is far away from the access point, or
something similar), beacon frames are typically the only traffic that
you will see with those rates: so it may be safe to assume that those
frames you are seeing are in fact beacons (or it may not, depending on
what sorts of wifi devices you have around).
If you get bbn_80211b_tap.py running you should be able to run either
tcpdump or wireshark on the tap/tun interface it creates and you can get
some more information about the packets.
Doug

Doug G.
Research Assistant
Communications and Signal Processing Lab
Oklahoma State University
[email protected]
[email protected]
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