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Re: [Discuss-gnuradio] Gigabit ethernet
From: |
John Gilmore |
Subject: |
Re: [Discuss-gnuradio] Gigabit ethernet |
Date: |
Tue, 23 Nov 2004 01:13:26 -0800 |
> -max data rate ~750Mb/s, the rest is lost as signaling overhead
Actually it's better than that. With 1500 byte packet sizes the
Ethernet overhead is only a few percent, so well driven hardware runs
well over 950 Mbit/sec. IP and UDP would eat a bit more of that,
but it's only 28 out of 1500 bytes (another 2%).
GigE always runs full duplex, which is a big advantage over USB2. You
get the same bandwidth simultaneously in each direction (2 Gbit/sec
total) and they don't interfere with each other on the wire.
I'd skip using jumbo frames, since they're nonstandard and might not
work through various switches or networks. See:
http://darkwing.uoregon.edu/~joe/jumbos/jumbo-frames.pdf
> -gigabit ethernet interfaces are becoming common and cheap
True. But they don't exist on very many laptops, and it would be a
lot more work to make it ramp down to do the 100 Mbit Ethernet PHY
when plugged into one. (The USRP still won't run on USB1, only USB2;
Eric says it's too much work and he wants to clean that up later, or
preferably never.) I've only seen GigE on Apple laptops so far,
though I haven't looked very hard.
> -can remotely locate hardware
Well, if you have a gigabit fiber between the hardware and the PC...
or a 100m coax cable. But indeed 100m is further than USB cables go.
We did look at GigE. I think the big kicker was (1) we didn't expect
GigE on laptops as soon as USB2 on laptops, and (2) a very handy
PHY/controller chip was available for USB2.
But feel free to start hacking on one yourself, it would be useful!
Make it take the same daughterboards as the USRP...
John