In reply to a post by someuser08:

When they ask to reboot CBT it comes back up for anywhere from 5 to 60 min and then everything goes dead again.

A CBT is completely passive, it cannot be rebooted.

Did you mean reboot the ONT, i.e. the little box inside your house where the fibre terminates? I doubt they have been rebooting the OLT (the active equipment in the exchange) - that would affect hundreds or thousands of users.

If rebooting your ONT fixes it, then either the ONT is bad (in which case they'll swap it) or the light levels are borderline (but they'll be able to measure those). Or else it's something very funky, like spikes on the mains power, but that is highly unlikely.

Keep chasing your service provider. Make sure you get the daily compensation - use it to buy a 4G unlimited SIM. Escalate to Openreach CEO would probably be your next step.

In reply to a post by candlerb:

In reply to a post by someuser08:

When they ask to reboot CBT it comes back up for anywhere from 5 to 60 min and then everything goes dead again.

A CBT is completely passive, it cannot be rebooted.

Did you mean reboot the ONT, i.e. the little box inside your house where the fibre terminates? I doubt they have been rebooting the OLT (the active equipment in the exchange) - that would affect hundreds or thousands of users.

I'm sure its something to do with OLT (ONT can be rebooted to no avail, doesn't affect a thing) whether full thing or specific port is reset. An engineer mentioned that software can power signal to specific CBT(s) if it detects something faulty. That's why it comes back up from time to time. They checked it on the pole - no signal was there...

I'm also sure I'm the only connection on the CBT and the rollout is still ongoing on nearby streets, so its very new install altogether, so there can't be many users yet on it...

In reply to a post by someuser08:

In reply to a post by candlerb:

In reply to a post by someuser08:

When they ask to reboot CBT it comes back up for anywhere from 5 to 60 min and then everything goes dead again.

A CBT is completely passive, it cannot be rebooted.

Did you mean reboot the ONT, i.e. the little box inside your house where the fibre terminates? I doubt they have been rebooting the OLT (the active equipment in the exchange) - that would affect hundreds or thousands of users.

I'm sure its something to do with OLT (ONT can be rebooted to no avail, doesn't affect a thing) whether full thing or specific port is reset. An engineer mentioned that software can power signal to specific CBT(s) if it detects something faulty. That's why it comes back up from time to time. They checked it on the pole - no signal was there...

I'm also sure I'm the only connection on the CBT and the rollout is still ongoing on nearby streets, so its very new install altogether, so there can't be many users yet on it...

No that's not correct.

At the exchange the OLT (really just a very large Layer 2/3 switch) is a chassis with a series of active cards installed. Each of these cards has a series of optical ports (typically 8 or 12-way). Each of the optical ports then drives up to 32 end-user devices (the ONTs) on a Passive Optical Network or PON.

As the individual strand of fibre for a given PON leaves the exchange (amongst hundred of other similar fibre strands that make up a fibre spine cable) the fibre runs to an Aggregation Node where it is spliced to another strand of fibre in another cable that runs to a Splitter Node. This is where the (completely passive) optical splitters are located and the light from that one fibre from the exchange is split 32 ways - dividing the one strand of fibre and its light into each of 32 separate outputs. Each output at the splitter represents a single customer connection going to an ONT at the customer premises.

From the Splitter Node the fibre outputs are then connected to a sequential series of CBT's (connectorised block terminals). As the name suggests these are simply environmentally hardened terminal units that the drop fibre connection to an an individual property is connected to and thence to an ONT in the premises. These are located locally to the properties served, typically on top of poles or underground in chambers (depending on howe FTTP is reticulated in that area) and typically are sized as 4-way, 8-way or 12-way devices. The CBT is just a chunk of plastic with special sealed screw-in connectors for the optical terminals, for the drop fibre property connection, embedded in it.

In a user premises, when an ONT is first powered up (or reset) it undertakes a preset handshaking, authentication and registration process with the OLT at the exchange. The OLT authorises the ONT to 'speak' (transmit) on the PON and the OLT has the capability to specially exclude an ONT from participating in the PON. Basically the OLT can tell the ONT to shut-up and stop transmitting if the OLT thinks it a rogue device, faulty or otherwise shouldn't be part of the network. The OLT however cannot stop sending 'light' to an individual ONT, as the rest of the network is just a passive 'tree'.

Furthermore there is no way an OLT can in any way tell any other part of the network to power on or off - because the network is totally passive. The only active things on a PON are the OLT in the exchange and the ONT in the user premises - everything else in between is 'dumb' and just passes the light in either direction.

Edited by Pheasant (Mon 22-Nov-21 19:20:09)

I don't know what's going on then. I watched an engineer on the pole checking CBT with very low signal, then calling someone who able to remotely (not in the exchange) reset something and signal comes back for 5 min and then disappears again. And they did it twice! When signal comes back (overnight more often) I was able to check the speed and was full 500/75 that I was supposed to be getting. I might not understand how fibre work, but I recon if there was physical breakage somewhere I would never be able to achieve full speed for 30 min. Something must be triggering it though...

Faulty card or SFP or maybe just a bit of dirt/ contamination on the fibre. Trouble is it will probably mean taking offline everyone on that headend card so will need a planned engineering works (PEW) to be done during the night.

That makes sense - but why are BT Retail telling the OP that BT Wholesale engineers need to attend? That just makes no sense.

Yes, I guess it could be hardware, but as for bad splice/contamination - I find it hard to believe that simply by resetting something it can be working for X amount of time without issues...

Another thing I googled - it could be a major fault due to network design: they could have connected more nodes into splitters or aggregates than allowed/supported (not sure if it is possible). So depending on overall load of the network, parts of it could be going down intermittently. When engineers checked local splitter it was also without signal as was CBT... This could be a problem for a large area, but I might be very early adopter and they might not realise how big the problem is due to that.

In reply to a post by Pheasant:

That makes sense - but why are BT Retail telling the OP that BT Wholesale engineers need to attend? That just makes no sense.

Usual BS from their support I recon. I fully expect another regular OR engineer to turn up at my house tomorrow wondering why he was sent if the fault is outside.

If they come to your house and can't get light they should be escalating the cases though, it sounds like they're just closing them out each time and forcing you to have to keep hassling your ISP. Your ISP should be rejecting the fault clear each time.

The question to my mind is where does the OP best focus his energies on an escalation to resolve.

Personally after being out of action for nigh on three weeks I'd probably send a joint email of complaint to the CEO's of both BT Retail (Marc Allera), BT Customer Service Consumer (Nick Lane) and Openreach ([removed by tbb]) and tell them about how poorly joined up their service restoration process actually is....

Edited by seb (Mon 02-Feb-26 21:38:36)