FTTP repair process

After some enlightenment on process of fixing fibre faults. Had red LOS light on now for 11 days. Only had it for a couple of months, it may or may not be significant that the installation engineer said the light levels at the CBT was lower than expected, but still in range.
Openreach engineer attended next day, diagnosed fault beyond the CBT, and referring it to others that cover the wider network.
Seems little information passed to ISP, who on todays update, stated it was down as wait resource allocation and fault was affecting multiple premises.
In the days of ADSL, fault fixing came primarily down to repairing bad connections.

I'm guessing on storm related damage and OR have been caught short dealing with a backlog of faults

After our end of village got FTTP it failed twice due to issues along the line, both times it took out all the properties. As I posted couple of years ago there will be issues, just not the same ones.

The fault happened the Tuesday before ISHA, but undoubtedly with the extended repair time is will now be a factor.

It would be interesting to know a bit more about how the fibre gets from the CBT to the OR kit (OLT?) where the optical links become ethernet or FCoE (not sure if OR use this).

I was wondering about resilience to power outages, with FTTC it seemed to hang in there until my own UPS had shut down if the mains was down for long enough, so far we have not had a mains outage since FTTP went live just before Christmas 2023.

There are some explanations about this around but the ones I found appear to be a little out of date as they don't mention CBTs, which I understand have a reflection port that can be used by OR to check that light is reaching the CBT (and allow diagnosis if an ONT loses signal).

Optics is rather different to RF with which I am much more familiar, I am not at all familiar about the splitting and combining of the optical signals as described. Time to do some more research I suppose.

The CBT to the ONT is all connectorised fibre as far as I can tell. The diagnostics seemed to be to check the light level at every joint, then declare it not getting to the CBT, and saying it needed one of the network guys. Unfortunately still waiting for a fix.
Again quite a bit of experience of 50Hz to RF in copper, but done nothing with optical fibre.

Yeah, I know all about lumped and distributed splitters and combiners for RF, diplexers etc, been doing it for 45 years plus, but optical stuff is just different.

I do like that good old optics lab warning notice:

"Do not look into laser beam with remaining eye!"

Openreach use PON, so for the majority of their FTTP there is nothing powered externally between the headend in the exchange and the ONT at the end user. Only exceptions are where they have utilised a remote headend to either extend the distance of the PON network or to save building extra fibre spine capacity.

Sounds to me like a break in the fibre cable somewhere.

The standard way to debug this is to use an Optical Time Delay Reflectometer (OTDR) to send light pulses down the fibre and time the reflections coming back. This gives a direct measurement of the distance to the break, or other anomaly like a faulty splice.

OTDR, correct me if wrong but doing test at at customer endpoint or telecom headend, would give same equivalent result. So there no need to conduct a test at customer end to be able to locate the location of fault.