I have been troubleshooting an issue with possible packet relflections and
cannot figure out the cause. I am running tunnel.py on two USRP2s that are
cabled together with a 20dB attenuator between them. The settings I am using on
both sides for tunnel.py are:
Tx Gain: 15 dB
Rx Gain: 10 dB
Carrier Threshold: -80
Rx Tunnel Freq: 400 MHz
Modulation: GMSK
Bit Rate: 1Mb/sec
When I use VLC to stream a video from computer A to computer B over the USRP
link it works ok but there are alot of reflected packs being recorded by
computer A. The same thing happens when I try to stream from computer A to
computer B. This also occurs when I use iperf to test the link. Strangely,
though there are NO reflected packets when I ping between the computers.
Below is a paste of some of the output from computer A. I put in a timestamp on
the left of when events occur. I also put in an explicit statement to print out
when tunnel is backing off and for how long. I added sequence number to make it
blatantly obvious that the computer is receiving its own packet. Any packet
with a sequence number beginning originates from computer A. If the packet
originated from computer B it shows up at RX_packet=none. As it shows computer
A is receiving its own packets!
[ 63.61 ] Tx: seq_no = 100054 | len(payload) = 1448
[ 63.61 ] Tx: seq_no = 100055 | len(payload) = 186
[ 63.61 ] Tx: seq_no = 100056 | len(payload) = 1310
[ 63.61 ] Tx: seq_no = 100057 | len(payload) = 1448
[ 63.61 ] Tx: seq_no = 100058 | len(payload) = 1021
[ 63.61 ] Backing off for 0.001 sec
[ 63.62 ] Backing off for 0.002 sec
[ 63.62 ] Backing off for 0.004 sec
[ 63.63 ] Backing off for 0.008 sec
[ 63.64 ] Backing off for 0.016 sec
[ 63.64 ] Rx: ok = True | seq_no = 100054 | len(payload) = 1448
[ 63.66 ] Backing off for 0.032 sec
[ 63.64 ] Rx: ok = True | seq_no = 100055 | len(payload) = 186
[ 63.66 ] Rx: ok = True | seq_no = 100056 | len(payload) = 1310
[ 63.66 ] Rx: ok = True | seq_no = 100057 | len(payload) = 1448
[ 63.67 ] Backing off for 0.064 sec
[ 63.67 ] Rx: ok = True | seq_no = 100058 | len(payload) = 1021
[ 63.72 ] Tx: seq_no = 100059 | len(payload) = 1448
[ 63.72 ] Tx: seq_no = 100060 | len(payload) = 70
[ 63.72 ] Tx: seq_no = 100061 | len(payload) = 1448
[ 63.72 ] Tx: seq_no = 100062 | len(payload) = 150
[ 63.72 ] Tx: seq_no = 100063 | len(payload) = 1448
[ 63.72 ] Tx: seq_no = 100064 | len(payload) = 248
[ 63.72 ] Backing off for 0.001 sec
[ 63.72 ] Backing off for 0.002 sec
[ 63.73 ] Backing off for 0.004 sec
[ 63.74 ] Backing off for 0.008 sec
[ 63.75 ] Backing off for 0.016 sec
[ 63.74 ] Rx: ok = True | seq_no = 100060 | len(payload) = 70
[ 63.75 ] Rx: ok = True | seq_no = 100061 | len(payload) = 1448
[ 63.76 ] Backing off for 0.032 sec
[ 63.75 ] Rx: ok = True | seq_no = 100062 | len(payload) = 150
[ 63.76 ] Rx: ok = True | seq_no = 100063 | len(payload) = 1448
[ 63.76 ] Rx: ok = True | seq_no = 100064 | len(payload) = 248
[ 63.78 ] Tx: seq_no = 100065 | len(payload) = 1448
[ 63.78 ] Tx: seq_no = 100066 | len(payload) = 566
[ 63.78 ] Tx: seq_no = 100067 | len(payload) = 1448
[ 63.78 ] Tx: seq_no = 100068 | len(payload) = 987
[ 63.78 ] Backing off for 0.001 sec
[ 63.79 ] Backing off for 0.002 sec
[ 63.79 ] Backing off for 0.004 sec
[ 63.79 ] Backing off for 0.008 sec
[ 63.8 ] Backing off for 0.016 sec
[ 63.8 ] Rx: ok = True | seq_no = 100066 | len(payload) = 566
[ 63.82 ] Backing off for 0.032 sec
[ 63.82 ] Rx: ok = True | seq_no = 100067 | len(payload) = 1448
[ 63.82 ] Rx: ok = True | seq_no = 100068 | len(payload) = 987
[ 63.84 ] Tx: seq_no = 100069 | len(payload) = 1448
[ 63.84 ] Tx: seq_no = 100070 | len(payload) = 1448
[ 63.84 ] Tx: seq_no = 100071 | len(payload) = 1448
[ 63.84 ] Tx: seq_no = 100072 | len(payload) = 321
[ 63.84 ] Tx: seq_no = 100073 | len(payload) = 1448
[ 63.84 ] Tx: seq_no = 100074 | len(payload) = 855
[ 63.84 ] Backing off for 0.001 sec
[ 63.84 ] Backing off for 0.002 sec
[ 63.85 ] Backing off for 0.004 sec
[ 63.85 ] Backing off for 0.008 sec
[ 63.86 ] Backing off for 0.016 sec
[ 63.87 ] Backing off for 0.032 sec
[ 63.86 ] Rx: ok = True | seq_no = 100070 | len(payload) = 1448
[ 63.89 ] Rx: ok = True | seq_no = 100071 | len(payload) = 1448
[ 63.89 ] Rx: ok = True | seq_no = 100072 | len(payload) = 321
[ 63.89 ] Rx: ok = True | seq_no = 100073 | len(payload) = 1448
[ 63.9 ] Backing off for 0.064 sec
[ 63.9 ] Rx: ok = True | seq_no = 100074 | len(payload) = 855
Does anyone have any idea why this could be occurring? I thought maybe it
would be a physical reflection but dont understand why ping packets would not
be reflected in that case.
Thanks,
Dave
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