Problem with BBN's 802.11 MAC

GNU Radio
1

Hi,

I am using gnuradio with BBN’s 802.11 mac in Ubuntu platform.

When I am using bbn_80211b_rx.py, I cannot capture any packet.
But, when I am transmitting using bbn_80211b_tx.py, I can capture all
the packets as transmitted by the transmitter.

Has anybody faced this problem?

Thanks and Regards,
Dola

2

Could you explain more precisely what you are doing, and what happens?

I have run the code under NetBSD with modified tap(4) driver that
handles 802.11 in addition to Ethernet. I am not clear on the state of
802.11 support in the Linux tap driver.

–
Greg T. [email protected]

3

When I run
./bbn_80211b_rx.py -v

I get the following output:

Bits Per Encoded Sample = 8
adc frequency = 64000000
decimation frequency = 16
input_rate = 4000000
gain = 45.0
desired freq = 2400000000.0
baseband frequency 2396000000.0
dxc frequency -4000000.0
Samples per data bit = 8

gr_fir_ccf: using SSE

No packet is captured.

However, when I use ./bbn_80211b_tx.py to transmit packets, I can
capture those packets and the output of ./bbn_80211b_rx.py -v is as
follows (with ./bbn_80211b_tx.py run in another terminal)

Bits Per Encoded Sample = 8
adc frequency = 64000000
decimation frequency = 16
input_rate = 4000000
gain = 45.0
desired freq = 2400000000.0
baseband frequency 2396000000.0
dxc frequency -4000000.0
Samples per data bit = 8

gr_fir_ccf: using SSE
uOPKT: 1, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=6981528,
rate=1 Mbps
PKT: 2, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=6993624, rate=1
Mbps
uOuOuOPKT: 3, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8045696,
rate=1 Mbps
PKT: 4, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8057792, rate=1
Mbps
PKT: 5, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8069888, rate=1
Mbps
PKT: 6, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8139992, rate=1
Mbps
PKT: 7, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8164184, rate=1
Mbps
PKT: 8, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8188376, rate=1
Mbps
PKT: 9, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8212568, rate=1
Mbps
PKT: 10, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8236760, rate=1
Mbps
PKT: 11, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8335648, rate=1
Mbps
PKT: 12, len=1477, rssi=-19, src=20:61:6e:64:20:73, time=8347744, rate=1
Mbps

The packet counts are not from original code, I printed them.

Thanks,
Dola

4

Are you trying to capture real 802.11 1Mbps packets, or what?

To do that you’ll need to do:

$ ./bbn_80211b_rx.py -f 2.462G -d 8 -b

gr_fir_ccf: using SSE
Packet received, length = 148, rssi = -15, rate = 1.0 Mbps
Packet received, length = 147, rssi = -40, rate = 1.0 Mbps
Packet received, length = 148, rssi = -16, rate = 1.0 Mbps

The -d 8 is so it gets enough of the spectrum, the -b is so it uses the
Barker spreading from the 802.11 spec.

However, I wouldn’t expect to receive much more than beacons, probe
requests and responses, and CTS-to-self for 802.11g protection mode. At
least that’s what I see in our wifi network.

-Dan

5

I think you should see real data packets at 1 Mb/s if there are any. I
would expect multicast in IBSS mode to be like this.

–
Greg T. [email protected]

6

Thanks a lot. This worked for me.

Dola

7

Greg T. wrote:

I think you should see real data packets at 1 Mb/s if there are any. I
would expect multicast in IBSS mode to be like this.

Sorry; I was unclear. Yes, if I put my laptop into 1Mbps mode then I can
see data packets. Even in 2Mbps mode (especially if I use the -p
option). I just don’t expect there to be any 1Mbps traffic on a modern
network.

-Dan

8

Actually, I mostly see u0 (which I believe is usrp overruns). However,
I did receive 2/3 packets.

Dola

9

Dan H. [email protected] writes:

Sorry; I was unclear. Yes, if I put my laptop into 1Mbps mode then I can
see data packets. Even in 2Mbps mode (especially if I use the -p
option). I just don’t expect there to be any 1Mbps traffic on a modern
network.

That makes sense. The environment we developed and tested this in was
IBSS mode, and there multicast packets are sent at the basic rate of the
IBSS. I think that’s required by the specification. But I realize that
I’m not normal to consider IBSS mode a normal case.