LAN and Telecom Cabling How to implement TDR in software?

Hi!

I wonder if anyone can help me understand something. I've just read the
whitepaper about the VCT Technology by Marvell and the TDR technique used.
I was just wondering, how did they implemented TDR in software? Did they
manufacture the NIC in such a way that it acts as a reflectometer or did
they program it? If it's the latter, how is that possible?

Thanks for your time. Have a nice day!

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NANewbie wrote:


As far as I know, there's no way to create a TDR, with a standard NIC.

This is probably true.  The PCI bus which carries the NIC interrupts
runs at 33 MHz.  That 30ns period is about 20 ft of signal in Cat5+.
So that's going to be the limit of resolution if you can program
the hardware to even be that good.  Some on-card special function
could be faster, but it will have to have a fast clock.

Pentascanners [et al] aren't cheap for good reason.

-- Robert

I've seen a reference to using a GB NIC, with the right software, as a
TDR.  I think "marvel" is always mentioned.

Given that one bit, at a BG rate, is about one foot (as a wildass
simplification and approximation) it's not out of the question.  The
software could do some sort of a statistical analyisis to get the
uncertaintity range down to a small number of feet.

Google finds this, along with other stuff.

http://www.marvell.com/products/transceivers/quadport/VCT_White_Paper.pdf




--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

Ah, but all four pairs are used in a fancy encoding scheme.
The transitions on any given pair are happening at 100 MHz,
or a period of 10 ns, about 2m/7ft wire.  Divided by two
since the reflection takes double.


Statistical analysis on digital signals?  Only if there's
big scatter or the signal is midrange so it splits.


Oh, if the software or hardware functionality is built-into
the GBE controller chip, resolutions down to it's clock
are possible.

-- Robert