Re: [Discuss-gnuradio] USRP2 / Tunnel.py packet reflection issue

I have been running into problems using tunnel.py as well so instead of creating a new post I thought I'll just continue this thread.

My setting:

USRP2

XCVR2450

Ubuntu 10.04 (32bit)

The problem I have is that after running tunnel, whenever I do ping, my system gets stuck on the ARP exchange. Say A wants to ping B. A broadcasts an ARP packet to find the MAC address of B's IP. B gets the ARP request, immediately sends an ARP response back to A with its MAC. However, in my system, A never gets the ARP reply. 

I seriously can't think of a reason for this. I can guess a possible cause is that B sends the ARP reply too quickly that A doesn't have enough time to go from transmit mode to receive mode (XCVR2450 is a half-duplex daughterboard). But I don't know how to verify this hypothesis.

Can anyone help me?

Thank you,

Johnny

On Thu, Oct 20, 2011 at 11:24 AM, Marcus D. Leech <mleech@ripnet.com> wrote:

On 20/10/2011 10:25 AM, David Barton wrote:

 

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

There's generally only about 45dB of isolation available between TX and RX, so if you're running in full-duplex, your receiver will see its
  own transmissions.

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