You'd hope it signifies a better capability in automatic testing of the line, which can then feed back at the time of sale.

If ISPs can be given a reliable indication of whether the A range or the B range applies, it gives some scope to upsell an engineer install.

Catch 22 though, you cannot make a test for a bridge tap on an FTTC circuit until the service is up and running.

I think it only appears with the telephone number chacker?

Yes.

In reply to a post by Zarjaz:

Catch 22 though, you cannot make a test for a bridge tap on an FTTC circuit until the service is up and running.

I have to admit that I though a TDR - when employed at the exchange end, say, as part of a test head - would highlight reflections from both the main pair and the tap.

Ah - that explains why I couldn't see it here

Think about it ...

As it is referring to a condition on a specific copper pair, it can only be returned on a telephone number check or for a specific line ID.

An address check cannot as there may be multiple lines serving that address.

It shows "N" for our number, which I expected. I presume if it says "Y" then the router is connected to an extension?

I seriously doubt that, and even then surely a TDR couldn't differentiate between those extensions connected after an SSFP or without.

It will certainly highlight the point at which the tap is connected and I too believe there may then be two reflections but discrimination may be difficult.

TDRs can be and are used to locate intercepts (wire taps) on phone lines too.

Some bare TDR waveforms can be found here:
http://pe2bz.philpem.me.uk/Comm01/-%20TestEquip/-%20...

The fifth one shows a few small reflections caused by taps, followed by an unterminated end.

The ninth one shows a splitter in use (probably on coax), with reflections for the 2 legs.

In raw terms, I'd expect a TDR to be able to show reflections from every termination of a line.

However, while this ought to apply to bare lines, I don't know how they'd apply to a BT line that properly terminates in a master.

I imagine that a filter (such as an SSFP) does a good job of hiding any taps that occur behind it ... which should be fine. Taps behind filters are good. Taps before filters are the bad ones.