Re: Muni fiber: L1 or L2?

[Jason Baugher <jason () thebaughers com>]

It's still a 23dB loss for each customer from the CO to the ONT.

I have an OLT that launches at +5dBm. At 1490nm, I should see about a .26dB
loss per km. My 1x32 splitter is going to add about 16dB more loss.
Assuming we ignore connector losses, and also assume that the customer is
10km away:

CO-based splitter:
+5dBm - 16dB - (10km x .26dB) = -13.6

Splitter at 9km:
+5dBm - (9km x .26dB) - 16dB - (1km x .26dB) = -13.6


If someone can explain why this math would be wrong, I'd love to hear it
and I'd be happy to run it past our vendor to see if they agree.


On Fri, Feb 1, 2013 at 3:16 PM, Owen DeLong <owen () delong com> wrote:

> Actually, this is an issue… I should have seen it.
>
>
> You have 3 loss components… Power out = (Power in - loss to splitter -
> splitter loss) / nOut - loss-to-customer
>
> So, if the loss to the splitter is 3db and you have 20db (effective 320db
> on a 16x split) loss on each customer link, that's
> a radically worse proposition than 20db loss to the splitter and 3db loss
> to each customer (which is effectively 48db
> loss on a 16x split).
>
> It's still do-able, but you either need amplifier(s) or very short
> distances between the customer and the MMR.
>
> Given this consideration, I think the situation can still be addressed.
>
> Put the splitters in the B-Box and allow for the possibility that each
> subscriber can be XC to either a splitter or
> an upstream dedicated fiber. The provider side of each splitter would be
> connected to an upstream fiber
> to the MMR.
>
> So, each B-Box contains however many splitters are required and each
> splitter is connected upstream to a
> single provider, but you can still have multiple competitive providers in
> the MMR.
>
> This setup could support both PON and Ethernet as well as other future
> technologies.
>
> Owen
>
> On Feb 1, 2013, at 1:04 PM, Jason Baugher <jason () thebaughers com> wrote:
>
> I should clarify: Distance x loss/km + splitter loss. = link loss.
>
>
> On Fri, Feb 1, 2013 at 3:03 PM, Jason Baugher <jason () thebaughers com>wrote:
>
> > I disagree. Loss is loss, regardless of where the splitter is placed in
> > the equation. Distance x loss + splitter insertion loss = total loss for
> > purposes of link budget calculation.
> >
> > The reason to push splitters towards the customer end is financial, not
> > technical.
> >
> >
> > On Fri, Feb 1, 2013 at 2:29 PM, Scott Helms <khelms () zcorum com> wrote:
> >
> > > Owen,
> > >
> > > You're basing your math off of some incorrect assumptions about PON.  I'm
> > > actually sympathetic to your goal, but it simply can't work the way
> > > you're
> > > describing it in a PON network.  Also, please don't base logic for open
> > > access on meet me rooms, this works in colo spaces and carrier hotels but
> > > doesn't in broadband deployments because of economics.  If you want to
> > > champion this worthy goal you've got to accept that economics is a huge
> > > reason why this hasn't happened in the US and is disappearing where it
> > > has
> > > happened globally.
> > >
> > >
> > > > Bottom line, you've got OLT -> FIBER(of length n) -> splitter ->
> > > > fiber-drops to each house -> ONT.
> > >
> > > So far you're correct.
> > >
> > >
> > > > All I'm proposing is making n really short and making "fiber-drops to
> > > each
> > > > house" really long.
> > > > I'm not proposing changing the fundamental architecture. Yes, I
> > > recognize
> > > > this changes the economics and may well make PON less attractive than
> > > other
> > > > alternatives. I don't care. That's not a primary concern. The question
> > > is
> > > > "can PON be made to work in this environment?" It appears to me that
> > > it can.
> > > >
> > >
> > >
> > > Here is where you're problems start.  The issue is that the signal *prior
> > > to being split* can go 20km if you're splitting it 32 ways (or less) or
> > > 10km if you're doing a 64 way split. AFTER the splitter you have a MAX
> > > radius of about 1 mile from the splitter.
> > >
> > > Here is a good document that describes the problem in some detail:
> > >
> > > http://www.ofsoptics.com/press_room/media-pdfs/FTTH-Prism-0909.pdf
> > >
> > >
> > > Also, here is a proposed spec that would allow for longer runs post
> > > splitter with some background on why it can't work in today's GPON
> > > deployments.
> > >
> > >
> > > http://www.ericsson.com/il/res/thecompany/docs/publications/ericsson_review/2008/3_PON.pdf
> > >
> > > --
> > > Scott Helms
> > > Vice President of Technology
> > > ZCorum
> > > (678) 507-5000
> > > --------------------------------
> > > http://twitter.com/kscotthelms
> > > --------------------------------