For reasons too long-winded to be interesting, we have two phone lines that are delivered over a single copper pair from the exchange. This is achieved by the magic of a DACS unit which effectively multiplexes two voice lines over one physical line. The way this is done means that the line is no use for ADSL, for example, but it’s fine for voice-only lines. However, because it’s been a requirement that all new connections can support an ADSL link, they’re no longer installed (so the Openreach engineers tell me).
For several years we’ve had an intermittent fault on the lines supplied from the DACS resulting in them becoming noisy to the point of unusability — we’d get no dial tone or calls dropping for example. Try to explain the situation to a BT call centre person however and you’re deep into a rabbit hole. They have absolutely no idea what a DACS is any more and the scripts they work from have no way of handling it. In our case the lines leave the DACS unit at our end (which is on the outside wall of the house) on separate cables and take completely separate paths to different parts of the property, yet when I call to report a fault that occurs on both lines at the same time the response is always to assume that the reason must be something we have changed on our side of the master socket. Pointing out that the lines are independent after the DACS seems most likely to elicit the response that I shouldn’t have put this weird DACS thing on the line and perhaps I should try removing it.
You’d hope (in vain, it seems) that BT would at least tell their fault systems people about hardware that was still in use but uncommon so they could deal with customers properly rather than driving them to distraction.
As it happens this time I reported a fault it was eventually referred to a group of engineers who actually really understand how things work after a few times around the same loop. It took him perhaps ten minutes at the most to diagnose the fault, a further five up a ladder at one of our nearby poles to remake the circuits and we were done. As a consequence of the work he also had to remake the circuit for the our ADSL line and as a result our ADSL link has increased in speed from “glacial” to “snail’s pace” which I count as a pretty good outcome. It’s hardly overwhelmingly impressive that it took so many visits to tie the problem down however.