Re: [Discuss-gnuradio] Explanation about gr0

[Josh Blum]

On 09/17/2012 08:58 PM, usrp n210 wrote:
> When we run tunnel.py we set gr0 interface as "sudo gr0 192.168.200.1".
> As per my understanding ,in tunnel.py internally maintains routing table
> like in NAT which has entry name as gr0 with mapping of

tunnely.py just opens a virtual ethernet interface. In the place of an
ethernet card, the tunnel.py application handles the inbound and
outbound ethernet traffic for this virtual interface.

The inbound and outbound packets interface directly with a packet framer
and packet correlation. Its so simple like that, there is no NAT involved.

> USRP IP address to gr0 IP address at network layer.So is my understanding
> correct?

The N120 interfaces with the PC using a network interface. But, hey,
some USRPs use USB. Basically, the fact that the USRP has an IP address
has zero relation to the IP addresses in the tunnel.py example.

> *and If I want to change or modify interface gr0 ,In what part of code I
> should look?*
> 

You can read more about tun/tap: https://en.wikipedia.org/wiki/TUN/TAP

If you are really trying to get into gnuradio. gnuradio-companion is
really the place to start. All of the modulation and framer blocks in
the tunnel.py example are in GRC with the GUI environment and all.

-josh