VS: Muni fiber: L1 or L2?
Henri Hannula
henri.hannula at msoy.fi
Fri Feb 1 22:59:46 UTC 2013
You propably calculated the second one (5 - 2.34 -16)-15 + 0.26 since you got -28.08
(5 - 16 - 2.6) - 15 = -28.6
(5 - 2.34 - 16) - 15 - 0.26 = -28.6
-Hena
-----Alkuperäinen viesti-----
Lähettäjä: Owen DeLong [mailto:owen at delong.com]
Lähetetty: 2. helmikuuta 2013 0:00
Vastaanottaja: Jason Baugher
Kopio: NANOG
Aihe: Re: Muni fiber: L1 or L2?
On Feb 1, 2013, at 1:43 PM, Jason Baugher <jason at thebaughers.com> wrote:
> 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:
>
Nope. The power going into each fiber out of the splitter is 1/16th that of what went into the splitter.
Yes, your total in-line loss is still 10km, but you are forgetting about the fact that you lost 15/16th of the power effectively going to the fiber when you went through the splitter (in addition to the splitter loss itself).
So: CO Based splitter:
Each customer gets (IN - 16dB - (10km x .26db))/32
Splitter at 9km:
Each customer gets (IN - (9km x .26dB) -16db)/32-(1km x .26db)
If we use 5dBm as our input, this works out:
CO: (5db - 16db - (10km x .26db) / 32
/32 is effectively -15 db (-3db = ½ power, 32 = 2^5)
Substituting: (5db - 16db - 2.6db) -15db = -28.6db to each customer.
Spitter at 9km: (5db - (9km x .26db) -16db)/32-(1km x .26db)
Substituting: (5db - 2.34db -16db)-15db-.26db = -28.08db to each customer
So there is a difference, but it seems rather negligible now that I've run the numbers.
However, it's entirely possible that I got this wrong somewhere, so I invite those more expert than I to review the calculations and tell me what I got wrong.
Owen
> 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 at 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 at 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 at 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 at 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
>> --------------------------------
>>
>>
>
>
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