Question for Zarjaz or anyone

Had an email earlier from Openreach regarding our FTTP build.

What could be the cause of "Light Loss" or similar holding our progress up.

Also what is the procedure for fixing it.

Re-Splice the fibre again. Just guessing.

Hi Mr P******

I have spoken to the delivery manager and she was aware that our contractors had been doing some light loss testing. She has advised that unfortunately these results won’t be accepted as there are still some build issues which will prevent acceptable results at the moment. These build issues are being looked at.

Regards Richard P*****
Infrastructure Solutions Executive Level Complaints Team
Openreach

Edited by busterboy (Sun 02-Aug-20 21:24:25)

In reply to a post by busterboy:

What could be the cause of "Light Loss" or similar holding our progress up.

Bad splices.

Also what is the procedure for fixing it.

Re-Splice the fibre again. Just guessing.

You guessed correctly.

That sort of problem can happen when Zarjaz hasn't done your installation.

Loss in fibre is down to:
- attenuation due to length, but for the total lengths involved with single mode fibre and the total lengths found in FTTP is not *really* a major concern.
- attention due to fibre connectors. Solution is to minimise the total number in a given link. Also APC style connectors are used in PON architectures to minimise the reflections / loss on the return path.
- attenuation due to splitters used in PON architectures. The designers know the limits here during design.
- attenuation due to splices. A good fusion splice is far superior than non-fusion here.
- attenuation due to fibre defects, either during manufacturing or install (crush, kink, too small bend radii etc)

All if the above can be estimated during design and measured following install using a combination of OTDR and light source and power meter.

And don't forget dirt on the connectors.

In reply to a post by candlerb:

And don't forget dirt on the connectors.

Never seen splicing done before but did watch the chap at the end of my drive when he was here.

I noticed he had a bottle of cleaning solution and wipes and did (at least when I watched him) cleaned every joint before using the splicer.

Fingers crossed for a quick fix tomorrow.

Splicer in use pictured here.

In reply to a post by candlerb:

And don't forget dirt on the connectors.

Absolutely. The ferule faces should be inspected (and cleaned) as a matter of routine before commissioning. Whether they actually are or not...

Would be interested to know if the issue is between the handover exchange and your local splitter or between the splitter and your CBT's.

Can add wrong SFP to list of possibilities

In reply to a post by witchunt:

Can add wrong SFP to list of possibilities

I’d put that into the “misconfiguration” bucket, rather than physical “light loss” or attenuation issue, which suggests (to me at least) a physical link issue.

I think many posters are reading the quote in the opening post incorrectly. Including the the OP himself.

It is stated that the light loss tests are being rejected because there are build issues that are being looked into.

That would tie in with the possibility of an incorrect SFP having been fitted, as suggested by witchunt. An SFP being a physical link.

Edited by RobertoS (Mon 03-Aug-20 23:03:22)

In reply to a post by RobertoS:

I think many posters are reading the quote in the opening post incorrectly. Including the the OP himself.

It is stated that the light loss tests are being rejected because there are build issues that are being looked into.

That would tie in with the possibility of an incorrect SFP having been fitted, as suggested by witchunt. An SFP being a physical link.

It could also mean the fibres might also be in the wrong trays at the Splitter Node resulting in the wrong fibre at the DP, they class that as a build issue too and it would also fail the light loss tests due to the engineer would be testing at the tray / fibre at the DP for that line which would be the incorrect fibre.

We had that same build issue at first which the engineer had to re-do all the fibres at our splitter node.

Once that was completed and commissioned off as complete our install went ahead.

Paul

In reply to a post by RobertoS:

I think many posters are reading the quote in the opening post incorrectly. Including the the OP himself.

It is stated that the light loss tests are being rejected because there are build issues that are being looked into.

That would tie in with the possibility of an incorrect SFP having been fitted, as suggested by witchunt. An SFP being a physical link.

Yes I read it as build issues for the area, maybe the road or neighbourhood that OP is in. Not for the actual final cable going to their house.

In reply to a post by Icaras:

Yes I read it as build issues for the area, maybe the road or neighbourhood that OP is in. Not for the actual final cable going to their house.

Correct because I haven't got any cable as yet running from the pole to my house.

Contractors working outside today so hopefully get to know something.

In reply to a post by RobertoS:

I think many posters are reading the quote in the opening post incorrectly. Including the the OP himself.

It is stated that the light loss tests are being rejected because there are build issues that are being looked into.

That would tie in with the possibility of an incorrect SFP having been fitted, as suggested by witchunt. An SFP being a physical link.

It's indeed possible. The OP quote mentions light loss testing - the classic method of which simply uses a light source and power meter to test the overall dB loss of the link meets the expected loss 'budget'. You can also use a power meter with the SFP driving the Tx side of link, effectively the light source, but needs measurement before and after any tail fibres are connected to determine the difference and whether there is a fault either with the SFP or cabling. Optical loss test should always be carried out from both directions as fibre can exhibit different forward and return loss.

Whilst I, in the meantime, have nowt to add to what others have said. Sorry.

In reply to a post by busterboy:

Contractors working outside today so hopefully get to know something.

As quoted Telent has been working today and installed this BT chamber like thing.

What it is I haven't a clue but hopefully we are a bit further.

Just this minute received another email from Openreach.

I will find out what’s still required and when whatever it is will be done and I will update you again on Thursday. I think it is just records and commissioning next, but will check and let you know.

Kind regards

R******

In reply to a post by RobertoS:

I think many posters are reading the quote in the opening post incorrectly. Including the the OP himself.

It is stated that the light loss tests are being rejected because there are build issues that are being looked into.

That would tie in with the possibility of an incorrect SFP having been fitted, as suggested by witchunt. An SFP being a physical link.

This may be pedantic semantics, and is not specific to FTTP or PON-based architectures but to fibre comms in general....

"Light Loss" refers to the physical difference in light level from end "A" to end "B"in a fibre link, attributable to the physical characteristics of the passive elements in the link. It is an absolute figure commonly defined in dB. An optical link, consisting of the various fibre plant, including fixed cabling, any jumpers/patch leads, splitters, connectors and splices all the way from end "A" to "B" will add to the overall "loss budget" of the link. If the measured loss (in either the forward or reverse direction) of a given fibre is beyond the design criteria of the link then it would not be deemed to "pass". Then there is the actual "optical budget" of the actual transceivers at either end of the link, this is set by the transceiver (SFP) manufacturers. The physical link loss budget <= the transceivers link loss budget or it simply wont work.

Then there is "Light Level". This is the absolute magnitude of the light either at source or destination. It can be expressed in several measures, but dBm is the typical one.

So a "fault" could be manifest because of excess "light loss" (aka link loss) or the absolute light levels do not meet spec.

An otherwise perfect physical link (correct link/light loss) could still fail on "light levels" if for example an SFP with the incorrect power level was used (too low or even too high) for the transmission distance.

In reply to a post by Pheasant:

This may be pedantic semantics, and is not specific to FTTP or PON-based architectures but to fibre comms in general....

"Light Loss" refers to the physical difference in light level from end "A" to end "B"in a fibre link, attributable to the physical characteristics of the passive elements in the link. It is an absolute figure commonly defined in dB. An optical link, consisting of the various fibre plant, including fixed cabling, any jumpers/patch leads, splitters, connectors and splices all the way from end "A" to "B" will add to the overall "loss budget" of the link. If the measured loss (in either the forward or reverse direction) of a given fibre is beyond the design criteria of the link then it would not be deemed to "pass". Then there is the actual "optical budget" of the actual transceivers at either end of the link, this is set by the transceiver (SFP) manufacturers. The physical link loss budget <= the transceivers link loss budget or it simply wont work.

Then there is "Light Level". This is the absolute magnitude of the light either at source or destination. It can be expressed in several measures, but dBm is the typical one.

So a "fault" could be manifest because of excess "light loss" (aka link loss) or the absolute light levels do not meet spec.

An otherwise perfect physical link (correct link/light loss) could still fail on "light levels" if for example an SFP with the incorrect power level was used (too low or even too high) for the transmission distance.

Mate.....

You have all this info inside you're head...

Kudos to you buddy, makes me look dumb.

That looks like a new JF4. The grass seed is a plus

In reply to a post by Zarjaz:

That looks like a new JF4. The grass seed is a plus

You will understand by reading this mate.