[160191] in North American Network Operators' Group
Re: Muni fiber: L1 or L2?
daemon@ATHENA.MIT.EDU (Owen DeLong)
Fri Feb 1 22:59:05 2013
From: Owen DeLong <owen@delong.com>
In-Reply-To: <14EB28242B5FC84E97BF638994426B58283457@posti2.msoy.local>
Date: Fri, 1 Feb 2013 19:54:24 -0800
To: Henri Hannula <henri.hannula@msoy.fi>
Cc: NANOG <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
OK... Like Einstein, math is not my strong suit.
Unfortunately, I don't have his prowess with physics, either.
Owen
On Feb 1, 2013, at 14:59 , Henri Hannula <henri.hannula@msoy.fi> wrote:
> You propably calculated the second one (5 - 2.34 -16)-15 + 0.26 since =
you got -28.08
>=20
> (5 - 16 - 2.6) - 15 =3D -28.6
> (5 - 2.34 - 16) - 15 - 0.26 =3D -28.6
>=20
>=20
> -Hena
>=20
> -----Alkuper=E4inen viesti-----
> L=E4hett=E4j=E4: Owen DeLong [mailto:owen@delong.com]=20
> L=E4hetetty: 2. helmikuuta 2013 0:00
> Vastaanottaja: Jason Baugher
> Kopio: NANOG
> Aihe: Re: Muni fiber: L1 or L2?
>=20
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> On Feb 1, 2013, at 1:43 PM, Jason Baugher <jason@thebaughers.com> =
wrote:
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>> It's still a 23dB loss for each customer from the CO to the ONT.=20
>>=20
>> 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:
>>=20
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> Nope. The power going into each fiber out of the splitter is 1/16th =
that of what went into the splitter.
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> 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).
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> So: CO Based splitter:
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> Each customer gets (IN - 16dB - (10km x .26db))/32
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> Splitter at 9km:
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> Each customer gets (IN - (9km x .26dB) -16db)/32-(1km x .26db)
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> If we use 5dBm as our input, this works out:
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> CO: (5db - 16db - (10km x .26db) / 32
> /32 is effectively -15 db (-3db =3D =BD power, 32 =3D 2^5)
> Substituting: (5db - 16db - 2.6db) -15db =3D -28.6db to each customer.
>=20
> Spitter at 9km: (5db - (9km x .26db) -16db)/32-(1km x .26db)
> Substituting: (5db - 2.34db -16db)-15db-.26db =3D -28.08db to each =
customer
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> So there is a difference, but it seems rather negligible now that I've =
run the numbers.
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> 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.
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> Owen
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>> CO-based splitter:
>> +5dBm - 16dB - (10km x .26dB) =3D -13.6
>>=20
>> Splitter at 9km:
>> +5dBm - (9km x .26dB) - 16dB - (1km x .26dB) =3D -13.6
>>=20
>>=20
>> 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.
>>=20
>>=20
>> 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.
>>=20
>>=20
>> You have 3 loss components. Power out =3D (Power in - loss to =
splitter -=20
>> splitter loss) / nOut - loss-to-customer
>>=20
>> So, if the loss to the splitter is 3db and you have 20db (effective=20=
>> 320db on a 16x split) loss on each customer link, that's a radically=20=
>> worse proposition than 20db loss to the splitter and 3db loss to each =
customer (which is effectively 48db loss on a 16x split).
>>=20
>> It's still do-able, but you either need amplifier(s) or very short =
distances between the customer and the MMR.
>>=20
>> Given this consideration, I think the situation can still be =
addressed.
>>=20
>> Put the splitters in the B-Box and allow for the possibility that =
each=20
>> subscriber can be XC to either a splitter or an upstream dedicated=20
>> fiber. The provider side of each splitter would be connected to an =
upstream fiber to the MMR.
>>=20
>> So, each B-Box contains however many splitters are required and each=20=
>> splitter is connected upstream to a single provider, but you can =
still have multiple competitive providers in the MMR.
>>=20
>> This setup could support both PON and Ethernet as well as other =
future technologies.
>>=20
>> Owen
>>=20
>> On Feb 1, 2013, at 1:04 PM, Jason Baugher <jason@thebaughers.com> =
wrote:
>>=20
>>> I should clarify: Distance x loss/km + splitter loss. =3D link loss.
>>>=20
>>>=20
>>> 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 =3D total =
loss for purposes of link budget calculation.
>>>=20
>>> The reason to push splitters towards the customer end is financial, =
not technical.
>>>=20
>>>=20
>>> On Fri, Feb 1, 2013 at 2:29 PM, Scott Helms <khelms@zcorum.com> =
wrote:
>>> Owen,
>>>=20
>>> You're basing your math off of some incorrect assumptions about PON. =
=20
>>> I'm actually sympathetic to your goal, but it simply can't work the=20=
>>> way you're describing it in a PON network. Also, please don't base=20=
>>> logic for open access on meet me rooms, this works in colo spaces =
and=20
>>> carrier hotels but doesn't in broadband deployments because of=20
>>> economics. If you want to champion this worthy goal you've got to=20=
>>> accept that economics is a huge reason why this hasn't happened in=20=
>>> the US and is disappearing where it has happened globally.
>>>=20
>>>=20
>>>> Bottom line, you've got OLT -> FIBER(of length n) -> splitter ->=20
>>>> fiber-drops to each house -> ONT.
>>>>=20
>>>=20
>>> So far you're correct.
>>>=20
>>>=20
>>>>=20
>>>> All I'm proposing is making n really short and making "fiber-drops=20=
>>>> to each house" really long.
>>>> I'm not proposing changing the fundamental architecture. Yes, I=20
>>>> recognize this changes the economics and may well make PON less=20
>>>> attractive than other alternatives. I don't care. That's not a=20
>>>> primary concern. The question is "can PON be made to work in this =
environment?" It appears to me that it can.
>>>>=20
>>>=20
>>>=20
>>> Here is where you're problems start. The issue is that the signal=20=
>>> *prior to being split* can go 20km if you're splitting it 32 ways =
(or=20
>>> less) or 10km if you're doing a 64 way split. AFTER the splitter you=20=
>>> have a MAX radius of about 1 mile from the splitter.
>>>=20
>>> Here is a good document that describes the problem in some detail:
>>>=20
>>> http://www.ofsoptics.com/press_room/media-pdfs/FTTH-Prism-0909.pdf
>>>=20
>>>=20
>>> Also, here is a proposed spec that would allow for longer runs post=20=
>>> splitter with some background on why it can't work in today's GPON=20=
>>> deployments.
>>>=20
>>> =
http://www.ericsson.com/il/res/thecompany/docs/publications/ericsson_
>>> review/2008/3_PON.pdf
>>>=20
>>> --
>>> Scott Helms
>>> Vice President of Technology
>>> ZCorum
>>> (678) 507-5000
>>> --------------------------------
>>> http://twitter.com/kscotthelms
>>> --------------------------------
>>>=20
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