How to implement TDR in software?
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Posted by NANewbie on August 29, 2005, 8:53 am
Please log in for more thread options 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! ------------------------------------- ##-----------------------------------------------## Article posted with Cabling-Design.com Newsgroup Archive http://www.cabling-design.com/forums no-spam read and post WWW interface to your favorite newsgroup - comp.dcom.cabling - 2335 messages and counting! ##-----------------------------------------------## | |||||||||||||||||||||||||||||||||||||
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Posted by James Knott on August 29, 2005, 8:58 am
Please log in for more thread options NANewbie wrote: As far as I know, there's no way to create a TDR, with a standard NIC. | |||||||||||||||||||||||||||||||||||||
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Posted by Robert Redelmeier on August 29, 2005, 1:46 pm
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> NANewbie wrote:
>> 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? > 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 | |||||||||||||||||||||||||||||||||||||
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Posted by Al Dykes on August 29, 2005, 11:43 am
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>> NANewbie wrote:
>>> 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? >
>> 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. | |||||||||||||||||||||||||||||||||||||
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Posted by Robert Redelmeier on August 29, 2005, 4:09 pm
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> Given that one bit, at a BG rate, is about one foot (as
> a wildass simplification and approximation) 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. > 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. Statistical analysis on digital signals? Only if there's big scatter or the signal is midrange so it splits. > http://www.marvell.com/products/transceivers/quadport/VCT_White_Paper.pdf
Oh, if the software or hardware functionality is built-into the GBE controller chip, resolutions down to it's clock are possible. -- Robert | |||||||||||||||||||||||||||||||||||||
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>
> 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?