Re: [Discuss-gnuradio] updated packet format on USRP inband signaling

[Eric Blossom]

On Tue, Feb 27, 2007 at 07:49:02AM -0500, Greg Troxel wrote:
>   I'm thinking layer 2 with a unique Ethernet packet type (probably use
>   some abandoned packet type).  That said, there's nothing stopping us
>   from doing UDP, except the additional bandwidth.  I don't see any need
>   to do TCP.
> 
> I think that it should be possible for an unprivileged user (on most
> Free systems) to interact with a USRP over GigE.  Actually this raises
> the issue of authorization and confidentiality/integrity of the data,
> probably taken care of by a dedicated ethernet port.

Under GNU/Linux they may need to be holding CAP_NET_RAW, since I
think the way to get the raw ethernet frames is with libpcap and/or
opening a raw socket using socket(PF_PACKET, SOCK_RAW, ...)

Actually, according to man 7 packet, socket(PF_PACKET, SOCK_DGRAM, 
hton(ETH_P_foo)) 
may work too.  It's been a while since I played with this stuff.

Any idea how we would get this done under *BSD?

I'm hoping on suitable machines to be able to run near wire-speed, so
that also argues for a dedicated ethernet port.

Also, absent some driver hacking to mux and demux commands and
responses, we may need a user space process to handle that stuff.  In
that case, only that processes would need access to the magic socket,
and the rest of the user code would use some kind of IPC to talk to
that one.

> USB is said to be reliable.   Presumably you mean to have that same
> property via pause frames.

Pause frames provide flow control.  According to folks at Vanu
(who use Gigabit ethernet to implement their basestations), that's
been sufficient, assuming any switches along the way aren't brain
damaged. 

If somebody wanted to ship samples a long way reliably, then some
higher-level protocol is probably in order.

Eric