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Is a optical network terminal (ONT) a modem? (hexbear.net)

submitted 1 week ago* (last edited 1 week ago) by trompete@hexbear.net to c/technology@hexbear.net

9 comments fedilink hide all child comments

Definition given by Wikipedia:

A modulator-demodulator, commonly referred to as a modem, is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carrier wave signals to encode digital information, while the receiver demodulates the signal to recreate the original digital information.

So fiber optics are not analog, but then again, neither are modern phone lines that use VoIP. No analog (as in analogous to sound waves) signal goes over them, both ends are permanently connected to modems. Yet it's still called a modem.

I think that turning a laser on and off can technically be described as modulating a carrier wave, so that part of the definition fits.

The ONT is fulfilling the same function as a modem, except the medium is a fiber optic cable instead of a copper one, so that makes me want to call it a modem by analogy. An electric burner doesn't burn anything either.

Thoughts?

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[–] trompete@hexbear.net 3 points 1 week ago* (last edited 1 week ago) (1 children)

Very interesting, thanks.

My ISP here in Germany gave me a separate ONT, to connect via ethernet to the router (they also gave me new router, with integrated DSL modem (lol), but I'm pretty sure the old one would have worked fine). I hooked up my own OpenWrt router instead. I'm happy they gave me a separate ONT, means I don't have to buy my own ONT or router that can do fiber to keep using the OpenWrt router. It in fact connects exactly the same as when it was hooked up to the DSL modem. Same PPPoE configuration, same VLAN even.

Which is why I was wondering if technically it's a modem, whether calling it a modem is incorrect. I'd say an integrated modem is still a modem, so I'm not fussed about the modem-vs-router distinction.

I don't think I have a way to see all this info you're talking about, but that would be interesting. Maybe I'll look into if you can connect to the ONT via HTTP or something and see that stuff.

There used to be a DSL router in the apartment building basement, but that stuff wasn't old, they only put in FTTB a couple of years ago. Recently they ran fiber into all the apartments and got rid of the DSL. Since you explain with the PON being easier/cheaper, I imagine that's what they did since they were able to build the whole thing throughout the city in last two decades, so they would have planned for that.

Anyway, I guess you didn't call the ONT a modem, but is it wrong to call it that? It modulates the laser on the fiber optic line, and it literally replaced a DSL modem which everyone agrees should be called a modem.

[–] invalidusernamelol@hexbear.net 2 points 1 week ago (1 children)

If you have FTTB, your ONT is probably a modem since the PON ends once it hits the building server room. We will usually allocate an unsplit distribution fiber to multi tenant buildings, then the building owner contracts with the ISP or some other company to handle the internal stuff.

My ONT is fiber to the home, so it's literally just a box that converts the raw fiber signal to a SFP connector.

[–] trompete@hexbear.net 2 points 1 week ago* (last edited 1 week ago) (1 children)

It used to be FTTB (DSL from there), only installed a couple of years ago, but recently they ran fiber into all the apartments. There's a new thin plastic cabinet, about 40x40 cm, in the bike cellar (server room lol) with a laser warning sign on it. All done in cooperation with the ISP it seems. In fact the landlord seemed utterly uninvolved.

Also why would it be called a modem in one situation, but not the other? Like what's the difference here.

[–] invalidusernamelol@hexbear.net 2 points 1 week ago* (last edited 1 week ago)

ONTs generally do less work than modems from my understanding. I deal primarily with PON so to me it's all physical fusion splices. We have done some work with older Coax networks, and those have a lot more active mux/demux equipment (as well as powered signal repeaters, which don't really exist on a PON) all over the place to cram as much bandwidth as possible into a single copper cable. That's not really a problem with fiber until you hit an OLT cabinet.

I would also like to add that the terminology in telecom is absolutely insane. It's up there with the oil industry when it comes to acronyms and multiple names for the same thing. We also frequently use "Transmedia" to refer to the cables and we call enclosures "closures".