How does splicing / splitting work?

You have a 'spine' of fibre running down a road with - lets just say - ten strands of individual fibres. At some point you need to split off one fibre, send it to (up to) 32 houses down a side road. How is the main cable physically split? Is it unsheathed and a fibre exposed?

Then you have nine strands continue down the main road. At this point there are still ten but one is unlit and redundant? At some point are there more redundant strands, or at some point does is the cable replaces with ( say) one containing four individual fibres?

I don't know why, but I need to know!

In reply to a post by Woolwich:

You have a 'spine' of fibre running down a road with - lets just say - ten strands of individual fibres. At some point you need to split off one fibre, send it to (up to) 32 houses down a side road. How is the main cable physically split? Is it unsheathed and a fibre exposed?

Then you have nine strands continue down the main road. At this point there are still ten but one is unlit and redundant? At some point are there more redundant strands, or at some point does is the cable replaces with ( say) one containing four individual fibres?

I don't know why, but I need to know!

Working backwards: at the endpoint, there are CBTs with say 4 or 8 or 12 ports. They are sized to cover the number of properties served.

As I understand, generally each CBT has its own cable all the way back to the splitter node - e.g. for a 12-port CBT there will be a 12-fibre cable running straight to the splitter. In principle a splice joint *could* be put along the route, but they really prefer not to do this.

At the splitter node, the appropriate number of fibres from each CBT will be attached to a splitter (these are tiny by the way, smaller than a matchbox - with fibre pigtails coming out into separate trays). If the splitter node serves more than 32 properties then there will multiple splitters.

From there, there are cables which run back to the fibre aggregation node, lighting a strand for each splitter. Again, it's *possible* to have splices along the route, but they prefer not to do that, since each splice is potentially a weakness.

For my FTTPoD install, I was talking to the engineers about this. They said that initially they had considered running a cable in sections with 4 or 5 splices along the route - presumably that would make it easier to branch off later to serve other splitter nodes. In the end they decided to do the "traditional" approach of pulling a subduct (tube) all the way from the fibre aggregation node to my splitter node, and blowing a cable in one piece through that. More reliable.

They haul up fibre cables from the ocean floor, open them up and splice in joints on a ship in the middle of the ocean. It's only weak if you are not doing it properly.

Ask the people doing that job if they would rather break into an existing armoured cable or access it at a point designed for splitting, hence called a splitter.

Also what they do on sub sea cables is a whole different league of costs e.g. if running a new fibre is cheaper they would do that rather than disturb an active cable.

I have been trying to understand how Openreach plans and builds their fibre network and your comments on splicing/splitting help but don't answer all my questions. I am lead in a Community Fibre Partnership for a community of some 40 properties. We now have funding in place and the project is being handed over to the delivery team. We have an aggregation node already in the middle of the village (part of a DSSB project that did not get completed).
To complete the build requires filling gaps in the fibre spine to the village. There are a couple of isolated properties that this spine will pass that I tried to get included in the project but this was declined although they could have been included if we enlarged the CFP to cover a much bigger area. This I declined as being unmanageable. Whilst I appreciate one cannot just break into a fibre and pick up a twisted pair as would happen with copper, how will Openreach connect individual isolated properties? Does each one need an individual fibre running back to a remote aggregation node or can joints be spliced in along the way? I believe that fibre now comes in various formats including armoured surround that does not need a duct or will every property need a mini duct of some sort that could have to run for miles?

I was confused by these two conflicting comments in your post

In reply to a post by chriswillsher:

We have an aggregation node already in the middle of the village

In reply to a post by chriswillsher:

To complete the build requires filling gaps in the fibre spine to the village.

Believe it or not the aggregation node was installed in the ground outside my house in 2017. I have photos to show it. Last year Openreach contractors returned and installed fibre splitters and CBTs on the poles around the village and we were expecting to be able to order FTTP soon. We had been "in scope" for FTTP since 2015. Then everything halted and we were told that 1.5Km of ducting needed replacing and the fibre link to the village was incomplete. The DSSB project was terminated. All efforts to get the job finished - letters to politicians, pleas to Openreach etc failed and a CFP became the only way to get the job finished. As it was assumed it would be completed under DSSB it was left out of the successor R100 plan and the checker showed "no plans". Helped by a contact in the Scottish government I established the CFP and now the Openreach cost will be fully funded by the Gigabit voucher scheme with the local supplements. Vouchers have been pledged and validated for this.
So you see, we have had the local infrastructure for some time but it isn't connected to the main fibre spine which runs along a main A road some 4 Km away.

In reply to a post by chriswillsher:

everything halted and we were told that 1.5Km of ducting needed replacing and the fibre link to the village was incomplete.

OK so you're saying you have an aggregation node in the village but it's not actually connected back to an exchange as its got at least 1.5Km of multi core fibre that needs replacing along the run to the exchange. Does that mean you have no FTTC in your village?

In reply to a post by dect:

Does that mean you have no FTTC in your village?

That's correct. We are a 100% EO line area with just ADSL. Not a green cabinet anywhere in the area.

In reply to a post by chriswillsher:

Believe it or not the aggregation node was installed in the ground outside my house in 2017. I have photos to show it.

How sure are you off that? I've lost count the number of assumed Agg Nodes that were Splitters.

How big is your town?

How far is the next nearest town?

How far is the nearest FTTC?

Splitters look almost identical to Aggregation Nodes.

Aggregation Nodes also serve the FTTC cabinets with fibre and have for years.
Aggregation Nodes serve (up to) around 1400 homes with FTTP.
They're usually installed after the spine is in place.

The vast vast vast majority of small towns will have half a dozen/a dozen Splitters but no Aggregation Node.