[160189] in North American Network Operators' Group
Re: Muni fiber: L1 or L2?
daemon@ATHENA.MIT.EDU (Leo Bicknell)
Fri Feb 1 19:44:10 2013
Date: Fri, 1 Feb 2013 16:43:56 -0800
From: Leo Bicknell <bicknell@ufp.org>
To: NANOG <nanog@nanog.org>
Mail-Followup-To: NANOG <nanog@nanog.org>
In-Reply-To: <CAMrdfRyQSC2Q0My12N-QXKk_ZOtvhCW6zC_9GAHF2rxf73G3_w@mail.gmail.com>
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In a message written on Fri, Feb 01, 2013 at 03:29:32PM -0500, Scott Helms =
wrote:
> You're basing your math off of some incorrect assumptions about PON. I'm
I'd like to know more about the PON limitations, while I understand
the 10,000 foot view, some of the rubber hitting the road issues
are a mystery to me.
My limited understanding is that fiber really has two parameters,
loss and modal disperson. For most of the applications folks on
this mailing list deal with loss is the big issue, and modal disperson
is something that can be ignored. However for for many of the more
interesting applications involving splitters, super long distances,
or passive amplifiers modal disperson is actually a much larger
issue.
I would imagine if you put X light into a 32:1 splitter, each leg
would leg 1/32nd of the light (acutally a bit less, no doubt), but
I have an inking the disperson characteristics would be much, much
worse.
Is this the cause of the shorter distance on the downstream GPON
channel, or does it have to do more with the upstream GPON channel,
which is an odd kettle of fish going through a splitter "backwards"?
If it is the issue, have any vendors tried disperson compensation with
any success?
The only place PON made any sense to me was extreme rural areas.
If you could go 20km to a splitter and then hit 32 homes ~1km away
(52km fiber pair length total), that was a win. If the homes are
2km from the CO, 32 pair (64km fiber pair length total) of home
runs was cheaper than the savings on fiber, and then the cost of
GPON splitters and equipment. I'm trying to figure out if my assessment
is correct or not...
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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