Network and infrastructure
VDSL
Acronym: VDSL
VDSL is the successor to ADSL on the copper pair: it offers much higher speeds, but only on short lines.
It uses a far wider frequency band than ADSL, which multiplies the speed as long as the line is shorter than about a kilometre; beyond that, attenuation pulls it back towards the performance of its predecessor. It served as a stopgap where fibre had not yet been rolled out.
Why it matters for fax
A VDSL plan is almost always fully unbundled access: the phone is provided by the router as voice over IP. For a fax machine, the situation is therefore that of fibre, not that of the old analogue line, even though the cable is still copper.