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Re: [Discuss-gnuradio] Running tunnel.py/benchmark tx.py (OFDM) with XCV

From: Florian Schlembach
Subject: Re: [Discuss-gnuradio] Running tunnel.py/benchmark tx.py (OFDM) with XCVR2450?
Date: Wed, 01 Feb 2012 18:05:53 +0100
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20111109 Thunderbird/3.1.16

We are now trying to establish an TCP/IP connection between both USRP2s
with the tunnel.py script.
Unfortunately, it says "Destination Host unreachable" when pinging the
other USRP. We should have set up the tunnel correct as some packets are
received and transmitted after having configured the IP address. The
pinged USRPs is indicating the received icmp packet but there is still
no confirmed ping-request though.

Short answer; dont do that. Yes, this particular USRP is a network
device, but that is completely unrelated to the purpose of tunnel.py.
You probably have to play with routing tables to make this work...

Why is that unrelated to the purpose of tunnel.py? Shouldnt a simple ping request be a basic application of using this TUN/TAP application? Anyway, we have now set up the routing table correctly by using TUN instead of TAP. As we are transmitting the ping from one of the USRPs, we are also receiving them at the RX-USRP which is answering with a ping reply:


Rx: ok = True  len(payload) =   84
Tx: len(payload) =   84
send now!

Observing the IP dataflow via Wireshark (at RX-USRP) confirms that.
However, we are NOT receiving this ping reply and the transmitting USRP.
It seems, like it cannot transmit and receive simultaneously. Exactky the same happens if we swap the role of transmitting and receiving USRPs.

Anybody has an idea how we could overcome this problem? Basically, we want to measure the latency of a "real" application.

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