Hack GPON – how to access, change and edit fibre ONTs

GPON is one of those technologies that should have been drowned in the bath before the spec even made it out of its ITU committee. It's just yet another patch papering over how cheap the ISPs were and how they continue to be. Yes, let's add another layer on top of all of the other layers. Now however many millions of links out to subscribers are hamstrung with that decision to split the physical layer up and throw in nonsensical TDM into the mix as well. Good luck squeezing much out beyond 25g in the future, you're just gonna have to rip all of that fiber up anyway and do home runs. Might as well have done it up front with all of the billions that have been given away to the littly piggy piggy ISPs.

I made a comment a few days ago about how I despair when I see anything modern datacenter related. I get the same sort of revulsion when I look at the list of all of the gpon hardware on that page and thing: how much duplicated and wasted effort has gone in to making dozens of different models of the exact same thing. A thing that's not really even needed if a halfway-competent ISP made an investment that's more than the absolute minimum required.

Nice directory democratizing some good reverse engineering, though!

</end soapbox>

I didn’t really understand the criticism. PON is just fine. I have an XGPON ONT and previously there was a GPON ONT. Upgrading was just getting one from the ISP after they upgraded the splitter. GPON and XGSPON can live simultaneously.

I don’t think we will ever hit the limits of PON quite frankly and swapping out PONs for newer and better standards is rather trivial.

I don't like PON either, and I applaud your soapboxing about it, but IMO this overstates the extent of the impending 'rip it all out and replace it'. They can keep most if not all of the fiber runs, and just switch the PON muxes out for DWDM muxes when they need a home run link to each customer.

It's equivalent to an old POTS party line, just with some makeup covering its shambling corpse (read: ITU G-number) and a bit more razzle-dazzle after strapping on some lasers. We can do better!

Yep, you could hack in some DWDM and scale with the capabilities of those endpoints, but at the end of the day it's still running over a shared medium. I don't think it's all impending doom and gloom, just a design decision that I think will not age well. It will be done eventually though I think.

Fiber investment in The Netherlands from the big telcos is now fully based on XGS-PON. Many homes that already had fiber installed do have the technically superior AON (a dedicated fiber to the home), but it seems like investment in this infrastructure has stopped.

The current situation is one where XGS-PON users can get 5Gbps subscriptions, whereas AON users are stuck at 1Gbps - seemingly because the telcos aren’t upgrading their point-of-presence hardware to support anything beyond 1Gbps.

What are the alternatives with passive splitter hardware that can work underwater if shit happens?

i dislike shared media and overly complicated mac as well as the next guy.

25gbps being "short sighted" is a bit of a stretch imho (running with 100mbps dsl and not feeling disadvantaged yet)

> whereas AON users are stuck at 1Gbps - seemingly because the telcos aren’t upgrading

poor souls, though can we care about the low-end first?

I'm no fan of PONs myself[1], but realistically they do still represent more than order of magnitude improvement over copper (or wireless shudder), while also proven to be very economical to deploy. Lets remember that perfect is the enemy of good, I'd much rather have PON with 90% household coverage than active fiber with 10% coverage.

Practically also with 50G PON already being standardized and 200G in the horizon it will take decades before the limitations will be relevant; with typical 1:32 split you get comfortably 1G service to subscribers. I do expect gigabit connectivity to be generously good for 99% of users for long time.

It is also noteworthy that while PON was originally standardized as asymmetric, it seems like ISPs have had a change of heart and are widely deploying symmetric PON (i.e. XGS-PON). I don't know what is driving that change (Twitch streamers and Youtubers? :D) but I'm happy about that.

You blame ITU for PON, but IEEE has been pushing EPON (ethernet-PON) for almost as long (GPON ratified 2003, EPON in 2004). Ultimately standards organizations are driven by industry, not the other way around. With the industry having some very big players in it, I have no doubt that PONs would have happened regardless of their standardization status.

While PON is shared medium which is conceptually yucky, in consumer world its impact is less because lines are massively oversubscribed anyways. It doesn't make much difference if you have PON or active fiber if the bottleneck is the uplink.

[1] https://news.ycombinator.com/item?id=41634415

> It's equivalent to an old POTS party line

I strongly disagree. On a party line information flows along the copper cable to every connected endpoint bidirectionally. While it's true that incoming information flows to all subscribers, never does information that flows out and you only get scrambled data even on the incoming stream. So if you're trying to make a security argument: the system is also safe on a physical level.

> We can do better!

Depends on what "better" is. I was quite critical of PON in the past but I have come around. Practically at this point I think PON is a better way to run networks in most places. At one point you hit a bottleneck anyways and not having to run individual fibers makes for a more resilient and cheaper system.

> but at the end of the day it's still running over a shared medium

Everything is eventually a shared medium. You don't have your own fiber all the way to Facebook. So the question is just at which point do you share and that should be a decision made on throughput and cost.

> poor souls, though can we care about the low-end first?

What is the low end? Austria has a similar problem. There are some quite old and unmaintained AON networks where people are stuck with 100MBit whereas even G.Fast copper eclipses that in some cities at this point.

Yes, exactly like one of those old copper POTS party lines - remember how providers could easily supply a reliable symmetrical multi-gigabit service over those (like we can with XGS-PON) and how they theoretically could use DWDM to move hundreds of gigabits over them? No??

They've also started replacing AON with XGS-PON in some areas, by putting all the fiber combining/muxing devices you need for that inside the AON POP building (and sending out new devices etc.)

For a while the maximum connection speed I could order was limited to 1 gbps. No XGS-PON here, the fiber rollout was 20 years ago in my neighbourhood so it's still the older standard. But interestingly they're now offering 4 gbps connections on the older standard as well.

I'm not sure how many home users order that, given the extra cost of 10g switches, NICs etc and then 90% of usage being via WiFi that only just makes it to 1 gbps. But it makes a lot of sense for businesses with multiple users sharing one connection.

Do they actually bury PON components? Because around here they don’t. Fiber runs from homes to their concentrators and those house both the PON splitters and the OLTs. There’s some roadside boxes as well but afaik they’re only for splices, because those aren’t buried, either.

> What is the low end?

from my pov: <100mbps

Even if you have AON you might have XGS-PON behind the scenes. In Switzerland end user fiber is AON more or less by regulation, but they just deploy the XGS-PON splitters in the COs.

> from my pov: <100mbps

Sure, but it's pretty ironic if you are stuck on a 100MBit fiber connection and a few buildings down you get 300MBit over twisted pair. And the problem with AON losing support is that you often can't find an independent ISP that would actually give you service over that AON you have.

Some providers do what imo is a best of both worlds approach here: Every customer has a full fiber run to the PoP, but there they use GPON to save on the active components. The actual fiber is pretty cheap compared to actually bringing it into the ground and that way you retain full flexibility.

The low end doesn't have to deal with AON vs GPON. They get DSL or DOCSIS, or if they're unlucky dial-up.

And when the poor souls on slow internet do get upgraded, AON vs GPON suddenly decides if they can get upgraded to the new higher speeds in the next ten years or not. 1gbps may be relatively slow in 10 years, but with a widely spread GPON you're not getting much more out of that, while with AON entire neighbourhoods can be upgraded by replacing a single rack in the local POP.

> but with a widely spread GPON you're not getting much more out of that, while with AON entire neighbourhoods can be upgraded by replacing a single rack in the local POP

Except in a few places it has been exactly the other way round. AON networks in Austria for instance have been built a few years back, some random companies ended up owning that infrastructure and don't upgrade. On the other hand the incumbents have built fiber, have rolled out GPON and have in the meantime upgraded to XGS-PON whereas many on AON got stuck. It's slowly moving but very gradually.

Yeah, as long as your ISP link isn't the bottleneck then it doesn't really matter if they are not as fast as they could be. I'm running on the cheapest FIOS plan and I can count on one hand the number of services where it is the bottleneck. In fact I can only thing of one at the moment: Steam, and even then only sometimes. Even then the difference is downloading a game in 12 minutes instead of 10 minutes assuming it isn't release week on a big game and the servers are slow.

Where I am, the low end are all on 4G/5G, as the plans are cheaper and don't require contracts or construction fees like wired internet.

PON generally uses PLC splitters which are pretty much wavelength agnostic, so you don't even need to swap out the splitters in outside plant. It it entirely possible to overlay DWDM wavelengths on PON segments without even removing or changing any of the PON equipment, making it possible to do a customer by customer migration from PON to DWDM if desired. You do end up having to use 80 or 100km optics to compensate for the insertion loss of the splitter, but it's not like even 10Gbps DWDM optics are too expensive for that (they're on the order of $200 a piece). More important is the security concern as any customers on the PON segment would be able to snoop on traffic making use of MACSEC mandatory.

That said, it is unlikely that major telcos will deploy DWDM to the home outside of niche markets. The savings in feeder fibres costs are nice, but the bigger concern is that there is a very real cost to hosting enough ethernet switches to provide an ethernet port per customer. Most of the GPON deployments around where I live use 1:32 splits, but 1:128 is viable for residential subscribers at shorter distances and when using XGSPON or 10G-EPON (although I stick to 1:32 in my own network). With 48 ports in 1U of space a carrier can serve up to 1536 to 6144 customers in 1U with PON. That would be racks worth of equipment using 1:1 ethernet. DWDM-only would drive up operating costs for space, power, HVAC and equipment maintenance by orders of magnitude.