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Re: [Discuss-gnuradio] Beacon frames of BBN 802.11

From: Jane Chen
Subject: Re: [Discuss-gnuradio] Beacon frames of BBN 802.11
Date: Sat, 21 Feb 2009 16:24:01 -0800 (PST)

Thank you for your reply!  I ran the ./bbn_80211b_tap.py and then I  used Ctrl-C to stop the bbn_80211b_tap.py.  After that I 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 <module>
    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__
  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,

From: Doug Geiger <address@hidden>
To: Jane Chen <address@hidden>
Cc: address@hidden
Sent: Saturday, February 21, 2009 8:52:34 AM
Subject: Re: [Discuss-gnuradio] Beacon frames of BBN 802.11

Hash: SHA1

Jane Chen wrote:
> Hi all,

> I ran bbn_80211b_rx.py and got the information as follows:
> PKT: len=163, rssi=-18, src="" time=13720, rate=1 Mbps
> PKT: len=163, rssi=-23, src="" time=21272, rate=1 Mbps
> .......

> //
> 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 Mbps
> 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!

> 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 Geiger
Research Assistant
Communications and Signal Processing Lab
Oklahoma State University
Version: GnuPG v2.0.10 (Darwin)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org


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