XDSL Internet Connection Over Optical Fibre Telephone Line?

Question

I have an ADSL2+ and a VDSL modems, and my flat has Optical Fibre for the telephone lines. I don't want to spend money on an FTTH modem since the ISP is limiting the speed and traffic of the Fibre plans. They are the same as the VDSL plans. There could be ping advantages in getting FTTH but I don't require it for my needs.

Are ISPs able to provide XDSL internet connection over Optical Fibre lines?

Because I've searched a lot for this, and from the ADSL and VDSL Wikipedia pages, I only see that they mention copper lines:

ADSL:

Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide.

VDSL:

VDSL offers speeds of up to 52 Mbit/s downstream and 16 Mbit/s upstream, over a single flat untwisted or twisted pair of copper wires using the frequency band from 25 kHz to 12 MHz.

Answer 1

Well, to begin with, you can see that your modem has an electrical connection for xDSL – but it does not have an optical input, so how are you going to connect the ISP's fibre? Only by using a converter. Either you use a device to convert the optical signal to copper Ethernet, or a device to convert the optical signal to copper VDSL, but you're going to need a converter one way or the other.

And the equipment you would need to provide your modem with an xDSL signal would cost several times more than a regular Ethernet converter, not to mention you'd be paying extra for the electricity. (Based on a quick ebay search, it seems even a used DSLAM might very well be into hundreds of dollars, whereas a GPON-to-Ethernet converter costs maybe $50.)

So converting to xDSL is only practical at ISP level. (Indeed ISPs very often just run fiber to the curb and use it to feed equipment which provides fast local VDSL for everyone on the street.) But it's not something you'll be able to get if you already have fiber directly at home, and honestly it's not something that would make any sort of practical sense to get at home.

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That said, the "fiber modem" does not need to replace your current router, it can act purely as a bridge (media converter or ONT). Some ISPs even provide the converter completely separately from the actual router so you can mix and match. Others bundle the ONT together with a complete home router in one device, but it's usually easy to switch that to "bridge mode" anyway.

So if you really want to continue using your current xDSL modem as a router, you can usually do so, as long as it can be configured to use Ethernet as WAN input.

Answer 2

No. They can't. The way DSL works is not compatible with optic lines. They could market something as DSL or DSL like but it wouldn't be. You'd need at he very least some form of media converter in between. They could provide you such a device, e.g. a regular phone won't be able to use an optic line either. They probably will integrate this into some kind of modem or router.

You might be able to use their "basic" device and chain your current one behind it depending on the connections available and types. This might lead to some other issues as you might be creating a NAT behind a NAT scenario.