IEEE 40GE & 100GE

Robert E. Seastrom rs at seastrom.com
Wed Dec 12 19:20:21 UTC 2007


"Chris Cole" <chris.cole at finisar.com> writes:

> One of the points made by Ted Sealy from Sprint is that they take
> advantage of the extra link budget in 10GBASE-LR 10km link budget to
> account for extra connector loss, etc.

Ted Seely and I are of the same mind on this.  2 dB sounds like plenty
for connector loss right up until you have to deal with multiple patch
bays in a structured system with amateurishly applied mechanical
splices.  The difference between noting that the loss is a little high
but the link still works so you roll with it, and having to spend time
on the phone arguing with someone who thinks 24 dB link loss is A-OK,
will make the slight additional up front cost for the better grade
optics look very inexpensive indeed...

> From this discussion it sounds to me like we should stick with 10km
> initially, and then later come back with an additional specification
> optimized for low cost, perhaps covering 2km.

I'm on board with that as far as it goes, but has the scenario of
adjustable launch powers so that you don't ever need attenuators plus
the economy of scale that would come from having *one* type of
interface for 1m-10km runs been considered?  It seems to me based on
what I've seen of the optics market that once you make something a
mass-produced commodity the price falls awfully far - suppose the
price difference was $250 vs. $375, that's a big difference on a
percentage basis but pocket change on an absolute basis.

                                        ---rob

>
> Chris
>
> -----Original Message-----
> From: Robert E. Seastrom [mailto:rs at seastrom.com] 
> Sent: Wednesday, December 12, 2007 5:06 AM
> To: Justin M. Streiner
> Cc: nanog at merit.edu; Chris Cole
> Subject: Re: IEEE 40GE & 100GE
>
>
> "Justin M. Streiner" <streiner at cluebyfour.org> writes:
>
>> I haven't read the draft spec yet to see what's being proposed for a
>> link budget at 3/4/10km, but that's just as important as the physical
>> distance.
>
> That's a really good point, and one which I didn't originally consider
> pre-coffee.  :-)
>
> Link budget information on page 4, here:
> http://www.ieee802.org/3/hssg/public/reach/Matsumoto_r1_1207.pdf
> Relative cost estimates on page 5.
>
> Suppositions for ingredients to link budget are here:
> http://grouper.ieee.org/groups/802/3/hssg/public/nov07/cole_01_1107.pdf
> (page 3)
>
> I'm kind of looking longingly at that extra 3dB, given the slight
> marginal extra cost and my knowledge of the trained chimp quality
> mechanical splices that are rife in certain <cough> data centers.
>
>                                         ---Rob



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