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Re: [Discuss-gnuradio] new 802.11b receiver

From: John Gilmore
Subject: Re: [Discuss-gnuradio] new 802.11b receiver
Date: Tue, 01 Apr 2008 09:36:23 -0800

> >> available? What causing the USRP2 can overcome the USB limitation ... ?
> >
> > USRP2 uses gigabit ethernet
> Yes, new USRP will support Gigabit Ethernet, but most computers don't 
> support that. You have to buy an extra card  or buscard for your 
> desktop or laptop.

Most applications of the USRP2 won't require the full bandwidth of the
GigE interface, just as most applications of USRP1 don't absolutely
max out the USB bus.  The USRP2 will also have a lot more processing
power next to the digitizers, so it can do the very highest bandwidth
calculation on-board, and only communicate lower bandwidth processed
signals with the host.

Most GigE implementations (and perhaps all certified ones) fall back
to 100 Mbit/sec or 10 Mbit/sec if plugged into a lower speed device.
Since the GigE in the USRP2 is implemented in free "software" in the
FPGA, that fallback code may be "unimplemented", at least in the
beginning.  Then again, 100 Mbit/sec may be the first Ethernet
implementation that works!

Whether or not low speed fallback is implemented, you should be able to
trivially interface a USRP2 to a lower speed Ethernet (e.g. on a
laptop) by plugging both into a $50 GigE switch, which will do the
rate adaptation for you.

This flexibility is just a piece of the power that comes from USRP2's
use of standardized Ethernet (and possibly IP) networking.


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