USRP2 with a Switch

Dear all,
We have 12 USRP2 boards which we would like to synchronise and run in a
phase array system as an expansion of the 4 element system we currently
have
running using the VRT branch of GNURadio.

Currently we use a 4 port PCIe Gb Ethernet Card to connect the USRP2
boards
to the host computer. Our Communications group suggested that we could
use
an Ethernet switch to support 12 boards instead of trying to find a
computer
we can stuff that many Ethernet cards in to.

Data from all 4 boards should get streamed into a data buffer on the
switch
and then be accessed sequentially by the host computer at a rate to
avoid
the over-run of the buffers. Switches work on the ethernet layer and
hence
the protocol should be compatible.

We have read about some problems on the forums regarding using a switch
for
the USRP2’s. Does anybody know if it is a realistic task to be able to
use a
switch to stream data in from multiple boards in this manner and how one
might start in creating a system which can do this? Does a new protocol
for
sending packets to the computer need to be created. If so then where is
the
current protocol specified?

Best regards,
Valentin.

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On Tue, Mar 23, 2010 at 09:54:37AM -0700, ValentinG wrote:

current protocol specified?

Best regards,
Valentin.

Are you transmitting or just receiving?

In an Rx only application, the switch will probably work out OK.
If you attempt to transmit, and the transmit data flow is not somehow
controlled on the host you’ll probably have a problem with the switch.

If you read and understand the gigabit ethernet specification on pause
frames and asymmetric flow control, you’ll have the background details
to reason about what you’re trying to do.

Eric

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