[hpsdr] Call for Comments and Discussion - OzyII

[Larry Gadallah]

2009/7/21 jeff millar <jeff at wa1hco.net>:
>
> If it's too soon for PCI-E for ham applications, Ethernet Layer 2 will do
> just fine. Stay away from a Layer 3 protocol, it doesn't serve any useful
> purpose.
>
> People keep equating Ethernet with TCP/IP. NOT TRUE!!! Ethernet has layer 2
> frames containing data addressed by MAC addresses. Layer 3 adds a lot of
> overhead, and features and uses IP addresses. For direct connected real time
> applications, stick to Layer 2 framing only.
>
> I've worked on a couple of projects embedding processors into FPGA's, using
> Xilinx MIPS. Disappointing in each case. Hooking the processor into the rest
> of the FPGA ended up taking a lot of logic resources. The software tools did
> not provide much confidence. It just didn't seem like it was worth the
> trouble. Altera NIOS might be better. But, overall I think you have be
> highly motivated to want to put a processor in the FPGA.
>
> I've also designed a system using USB for connecting to an SDR. ...also a
> somewhat disappointing experience. Achieving good performance required too
> many tricks. For Linux the trick are open, but for windows, there's a lot of
> secret sauce to make to work well.
>

I agree with Jeff regarding Ethernet layer 2 versus layer 3: Look at
this quote from the Wikipedia page describing ATA over Ethernet
(http://en.wikipedia.org/wiki/ATA_over_Ethernet):

"ATA over Ethernet (AoE) does not rely on network layers above
Ethernet, such as IP and TCP. In this regard it is more comparable to
Fibre Channel over Ethernet than iSCSI. While the non-routability
means AoE cannot be accessed over the Internet or other IP networks,
the feature makes AoE more lightweight (with less load on the host),
easier to implement, provides a layer of inherent security, and offers
higher performance. The AoE specification is 12 pages compared with
iSCSI's 257 pages"

To reiterate a comment I made earlier, if access to SDR data is needed
over the Internet, there are scads of general purpose, commodity
priced computers of every size and shape available, with existing
Operating Systems, TCP/IP stacks, Ethernet interfaces, and general
purpose CPUs that could act as routers/proxies between the Internet
and the LAN-attached SDR hardware.

-- 
Larry Gadallah, VE6VQ/W7                          lgadallah AT gmail DOT com
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