Muni fiber: L1 or L2?

Sat Feb 2 03:54:24 UTC 2013

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 at msoy.fi> wrote:

> 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
>>> --------------------------------
>>> 
>>> 
>> 
>> 
> 
> 