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Re: [Discuss-gnuradio] The ultimate SDR

From: John Gilmore
Subject: Re: [Discuss-gnuradio] The ultimate SDR
Date: Mon, 22 Oct 2001 20:42:40 -0700

> Assume we can utilize 50Mbit/sec of 100Mbit/sec ethernet (Is this a
> valid assuption?  What kind of throughput can actually be sustained?),

David Miller has pushed more than 10 mbytes/sec (user process to user
process) through a 100Mbit Ethernet, USING TCP under Linux!  So
clearly the raw hardware can move >80mbit/sec of payload info, even
when acknowledgement packets are interspersed with the data.  I would
have to dig around to get the actual max, but on switched twisted pair
you can run back-to-back packets containing 1500 bytes of payload
each, with only about a 20-byte header and a couple dozen bits of
framing on each end.  My guess is you get well over 95 mbit/sec if
your hardware is well designed.

Full duplex Ethernet gives you the entire available bandwidth in each
direction.  FDX is pretty standard in the 100mbit Ethernet controller
market.  It only works if there's a switch rather than a hub on the
other end, but the two ends negotiate this automatically when first
plugged in.  You could clearly require somebody doing this to use a
switch; they're cheap and tiny.  (Using a crossover cable between the
PC and the SDR box should also work, if the Ethernet controllers know
to negotiate FDX with another controller rather than with a switch.
I've had mixed results with that, while switch connections are


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