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Re: Going the distance


  With regards to the standards body "legislating under-achieving
link lengths to accommodate the simultaneous worst-case everything",
that is *exactly* what it must do -- because each vendor CAN build
their devices in the cheapest possible manner to meet the standard,
it is likely that SOME devices, links, etc. may be at some minimum
that the standard allows.  If we put out a standard that said "if
most of your equipment is better than our specs, only then can you
count on the distances we specify" it would be a worthless standard!!!

  Customers must be able to KNOW that if they buy a NIC from vendor A,
a switch from vendor B, have cable installed by vendor C, use patch
cables from vendor D, that as long as every vendor meets the standard,
it WILL WORK!  Extra distance, lower BER, etc. on top of this because
you choose to build your device/network using above-standard parts are
gravy, something that vendors can sell as "value added".  It is NOT
something that belongs in the standard, IMHO.

Bruce LaVigne

Larry Miller wrote:
> Ed,
> In our case the huge majority of increased link length came from the fact
> that the LX receivers are 6dB or more quieter than SX (or the standard), and
> on SM fiber this translates into a much larger link budget. One of the
> reasons we standardized on this is that transceivers with lower noise seem
> to be more reliable as well.
> It was not until we got into some custom 50 km links that we had to go to
> "death ray" lasers of increased power.
> This was a case of getting a 2X improvement over the standard "for free".
> Obviously, this may not happen in the 10GbE world.
> I suspect that if the Committee, in its wisdom, legislates under-achieving
> link lengths to accommodate the simultaneous worst-case everything as was
> done in 802.3z, then we will have a similar phenomenon as we have today: if
> you cannot easily double the link lengths (at least) then you probably
> bought some pretty cheesy equipment. Sales people, I think, would rather
> have the standard reflect more closely what the technology will reliably do,
> not some pruned-back number that they have to talk around.
> Larry Miller
> Nortel Networks
org:Hewlett-Packard, Workgroup Networks Division
title:Design Engineer
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fn:Bruce LaVigne