There are two limitations - max distance due to both timing and light that are currently 60km but I think it’s theoretically limited at 100km. There is also a max difference between the closest and farthest ONT on any given port - and that is typically 20km or 40km, but some platforms will let you set something in-between 20 and 40km.
If you are using 20km optics the max split doesn’t matter. If you are using 40km optics and you can put at ONT at 1m and one at 20.001km and it should work, but the ONT at 21km won’t - unless you set the max differential to 40km. It costs you a bit of bandwidth to do. 60km are the same way - 20 or 40km max differential. The bigger issue with 40 and 60km optics is return loss. You can keep picking better optics at the OLT - A, B, C, C+ and increasing the output power, but the ONT’s are all the same output power, and they transmit back on the higher loss wavelength. The C and C+ optics have better receive sensitivity and additional error correction (FEC), but ultimately even though the ONT can hear the signal fine, it can’t communicate back to the head end. You will likely also find that when running at >30km the difference in ONT and OLT receive signals confuses the techs. They get very used to seeing receive light levels that about match - but forget that the 1577nm (0.2dB/km) downstream wavelength has much lower loss per km than the 1270nm (0.35dB/km) upstream wavelength. We ended having to build a tool to do the calculations for the techs: Customer:xxxxxxx-ont RX at the ONT: -14.9 dB TX from the ONT: 6.5 dB Expected Loss: 28.5 dB Actual Loss: 26.2 dB Difference: -2.3 dB RX at the OLT: -26.5 dB Expected Loss: 34.9 dB Actual Loss: 33 dB Difference: -1.9 dB Distance from OLT: 42.68 km Without it they tended to freak out - what’s wrong with the fiber - the ONT is at -14.9dB and the OLT is seeing -26.5dB? Do the math at 42.68km and they are both about 2dB better than the expected at that distance. This one is within 3dB of theoretical - and good to go. Mark > On Aug 19, 2025, at 4:55 PM, Chuck <[email protected]> wrote: > > There was in the beginning due to the timing and cuing of ONT upstream. It > was to ensure 32 ONTs could all be transmitting max traffic at the same time. > That is what Calix told me many years ago. > Sent from my iPhone > >> On Aug 19, 2025, at 11:50 AM, Josh Luthman <[email protected]> >> wrote: >> >> >> From what I've read, the issue was the timing between the farthest & closest >> ONT. There was no 20km timing limitation from OLT to anything. >> >> On Tue, Aug 19, 2025 at 12:39 PM <[email protected] >> <mailto:[email protected]>> wrote: >>> Original GPON specs had a timing limitation of 20 km. >>> >>> >>> >>> >>> >>> From: AF <[email protected] <mailto:[email protected]>> On >>> Behalf Of Josh Luthman >>> Sent: Tuesday, August 19, 2025 6:31 AM >>> To: AnimalFarm Microwave Users Group <[email protected] >>> <mailto:[email protected]>> >>> Subject: Re: [AFMUG] how is underground FTTH done? >>> >>> >>> >>> Class C optics are rated for 60km or 42mi. That's a hell of a distance >>> when you're only doing 1:32. We did 1:2 and 1:32 on the sixteenth PON port >>> until we built more to justify another OLT. >>> >>> >>> >>> On Mon, Aug 18, 2025 at 6:13 PM Chuck McCown <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> When you work out a 32:1 GPON, the timing distance limitations are >>> exhausted before you run out of light. Splits are a 3 dB loss. A good >>> splice will be .02dB. So don’t worry about splices. >>> >>> >>> >>> From: AF [mailto:[email protected] <mailto:[email protected]>] >>> On Behalf Of Dev >>> Sent: Monday, August 18, 2025 9:56 AM >>> To: AnimalFarm Microwave Users Group <[email protected] >>> <mailto:[email protected]>> >>> Subject: Re: [AFMUG] how is underground FTTH done? >>> >>> >>> >>> The thing with PON is that every time the light hits a splitter it loses a >>> bit of strength, so you sort of have to plan to use a little hotter SFP in >>> your OLT sometimes. Luckily, those are getting way cheaper nowadays, so >>> it’s not the end of the world, but you do have to plan for that. >>> >>> >>> >>> Plus, each splice you do cuts down the signal a bit more. Fusion splicers >>> only lose a tiny bit, but a physical connector can lose a bunch more, like >>> the equivalent of a mile or more of distance, and a piece of crud on an >>> uncleaned connector can lose 5 miles distance, so make sure you clean them >>> with those cheap cleaner tools. >>> >>> >>> >>> On Aug 18, 2025, at 8:39 AM, Josh Luthman <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>> >>> Splitters are waaay small. Smaller than a standard house key. >>> >>> >>> >>> What you are looking at is an MST terminal, looks like 8 ports. There can >>> be a splitter inside of that yes. You can have the MST with 8 fibers >>> splice to another 8 fibers or you can have what is in your picture have 1 >>> fiber in, split 1x8, and then have 8 ports out for the installers to simply >>> plug in to. >>> >>> >>> >>> If that MST is a 1x8, you can have a 1x4 before it, between the MST and >>> OLT. That makes for OLT -> 1x4 splitter -> 1x8 splitter/MST. That is >>> still a 1x32 split. >>> >>> >>> >>> On Mon, Aug 18, 2025 at 11:34 AM Ken Hohhof <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> I thought PON used like 16:1 or 32:1 splitters, and in this photo, I >>> assumed that’s what the black boxes were. >>> >>> >>> >>> From: AF <[email protected] <mailto:[email protected]>> On >>> Behalf Of Josh Luthman >>> Sent: Monday, August 18, 2025 10:16 AM >>> To: AnimalFarm Microwave Users Group <[email protected] >>> <mailto:[email protected]>> >>> Subject: Re: [AFMUG] how is underground FTTH done? >>> >>> >>> >>> Don't assume that about aerial. That's not how it works. Don't think >>> about it in terms of taps. >>> >>> >>> >>> Generally speaking, installations are PON. What we do is design the fiber >>> so we can hook up 100% of homes. We assign a color to every house. >>> >>> >>> >>> The first thing to think about is that you have to access the individual >>> strand out of the cable, be it 12/24/48/144/etc. That is done with a >>> SpliceCase or you splice on an MST for an ez mode plug. At Imagine we only >>> splice - no connectors, no MST, no plugs, etc. >>> >>> >>> Second thing is that when there's a cable up and down the road, you just >>> need access to it through the case/MST from the house. This can be from >>> the house to the handhole (concrete box in the ground) or you can run it >>> from the house to the handhole through some 1.25" duct to the next handhole >>> where there is one case. >>> >>> >>> >>> I can show you what it looks like if you don't get it yet. >>> >>> >>> >>> On Mon, Aug 18, 2025 at 11:11 AM Ken Hohhof <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> The fiber train left without me, so maybe someone here can help me >>> understand how the physical installation is typically done. >>> >>> >>> >>> I’ve seen aerial fiber and it’s pretty straightforward, I see splitters up >>> on poles maybe at each intersection, and to hook up a customer, they run a >>> drop wire from the nearest splitter to the house. If take rate is better >>> than expected or a new house is built, worst case I assume they just add a >>> splitter. >>> >>> >>> >>> But I also see FTTH deployments going in where they are boring for duct in >>> the ROW and putting a little handhole in front of every house. How does >>> this work? Are they using taps instead of splitters? If not, when they >>> get a customer install order, do they pull his drop cable through all the >>> handholes to a splitter? That doesn’t seem feasible. Are they dedicating >>> a strand to each house and pulling the main cable out each time and >>> splicing to that strand? And what if they estimate the take rate wrong, or >>> a new house is built? >>> >>> >>> >>> There’s probably a simple explanation and once someone enlightens me it >>> will be a Duh! moment. >>> >>> -- >>> AF mailing list >>> [email protected] <mailto:[email protected]> >>> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >>> >>> -- >>> AF mailing list >>> [email protected] <mailto:[email protected]> >>> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >>> >>> -- >>> AF mailing list >>> [email protected] <mailto:[email protected]> >>> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >>> >>> >>> >>> -- >>> AF mailing list >>> [email protected] <mailto:[email protected]> >>> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >>> >>> -- >>> AF mailing list >>> [email protected] <mailto:[email protected]> >>> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> -- >> AF mailing list >> [email protected] >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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