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:o...@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 <ja...@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 <o...@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 <ja...@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 <ja...@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 <khe...@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 >> -------------------------------- >> >> > >
