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Standard User Woolwich
(committed) Mon 11-Jan-21 17:29:47
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How does splicing / splitting work?


[link to this post]
 
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!
Standard User candlerb
(fountain of knowledge) Mon 11-Jan-21 20:28:21
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Re: How does splicing / splitting work?


[re: Woolwich] [link to this post]
 
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.
Standard User jabuzzard
(experienced) Mon 11-Jan-21 22:33:29
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
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.


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Administrator MrSaffron
(staff) Tue 12-Jan-21 09:34:43
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Re: How does splicing / splitting work?


[re: jabuzzard] [link to this post]
 
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.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User chriswillsher
(learned) Tue 12-Jan-21 09:50:15
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
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?
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 10:00:14
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
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.
Standard User chriswillsher
(learned) Tue 12-Jan-21 10:12:41
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
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.
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 10:29:19
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
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?
Standard User chriswillsher
(learned) Tue 12-Jan-21 10:32:39
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
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.
Standard User j0hn83
(fountain of knowledge) Tue 12-Jan-21 11:45:30
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
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.
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 11:57:02
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
Could you link to the pictures you have of what you believe is the aggregation node.
Standard User chriswillsher
(learned) Tue 12-Jan-21 12:33:31
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Re: How does splicing / splitting work?


[re: j0hn83] [link to this post]
 
It's a small central part of a scattered village, 12 miles west of Perth where the head exchange is located. Currently we get ADSL from Madderty exchange. The nearest FTTC cabinets are in Crieff, 5 miles to our west or Auchterarder, 5 miles south. We are told the fibre runs along the A85 between Perth and Crieff.

I will attempt to post a picture here of what I was told is an aggregation node. I took this back in 2016.

Better quality image - I hope

Edited by chriswillsher (Tue 12-Jan-21 12:37:38)

Standard User candlerb
(fountain of knowledge) Tue 12-Jan-21 13:23:48
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
In reply to a post by chriswillsher:
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?


Think of the FTTP design as a tree:

aggregation node --< splitter nodes --< CBTs

(root --< branches --< leaves)

The splitters are placed at locations in the FTTP design for that area, and each one covers a certain set of properties in its design footprint.

For the isolated properties: every one will be in the footprint of some splitter - which either already exists, or exists only on paper in a plan. The CBT(s) serving those properties will be connected back to that splitter, in a star arrangement.

If that splitter doesn't already exist, then that splitter will need to be installed, and a cable pulled to connect it back to its parent fibre aggregation node.

It's possible that part of the path back to the aggregation node is also taken by the cables to one or more other splitters. In that case, normally the cables will sit side by side in the same duct.

In reply to a post by chriswillsher:
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?


Fibre cables can also be run between poles. If the existing telephony service uses directly buried cables (Direct-In-Ground / DIG) then it is common for Openreach to install poles for fibre, rather than dig new ducts.

However if the existing service to the property is via underground ducts, usually they would re-use those. Such underground service can usually be identified by footway boxes in the pavement every few properties.
Standard User witchunt
(experienced) Tue 12-Jan-21 13:30:21
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
I'm pretty sure that's an aggregation node
Standard User Woolwich
(committed) Tue 12-Jan-21 13:58:04
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
In reply to a post by candlerb:
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.


So are you saying I'm backwards in my thinking? wink

Instead of wondering how a big fat cable is split up as it travels down a road, I should ask how all the small cables are joined as it goes up the road?

Er, is that why they're called aggregation nodes?
Standard User chriswillsher
(learned) Tue 12-Jan-21 14:16:59
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
Many thanks. That is helpful. Whether it is a primary splitter or an aggregation node in the manhole I am not certain but in any event, Openreach contractors have distributed the fibre around the village on the existing telephone line poles. Several of these also have what I assume are (Prysmian) secondary splitters on them leading up to CBTs on the tops.

We just now need to wait until they complete the link back to the main fibre spine some miles away. The initial work was all done in 2016, they came back and changed all the connections to the new type and installed secondary splitters and CBTs in May 2020 and then cancelled the whole project when they found a duct needed replacing! We were told that the DSSB (BDUK) project had finished leaving us in the lurch yet again. Hopefully having got a CFP confirmed they will finish the job this time?
Standard User shortshrift27
(learned) Tue 12-Jan-21 14:58:42
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
"secondary splitters": Does the agg node actually perform a splitting function? My working assumption was that each subscriber was at the end of 1 32-way split subsequent to the agg node and that the agg node served mainly to physically bundle fibres into larger trunk cables.

Written from a position of ignorance though, so genuinely happy to be corrected!
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 15:19:22
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
Can I ask how much in monetary terms you have been quoted to do the CFP to those 40 properties.
Standard User chriswillsher
(learned) Tue 12-Jan-21 15:39:41
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
In reply to a post by dect:
Can I ask how much in monetary terms you have been quoted to do the CFP to those 40 properties.

£108,000 or thereabouts. This is for 41 properties. I had another quote for 74 properties when I was considering a larger area to include some outlying clusters and that was nearly 4x as much. I may be talking rubbish but as the original work was aborted before completion, perhaps this includes the cost of the work already done as they might not have been paid for work that did not result in completed connections? Given that all that should now be required is 1.5Km of fibre in a duct that seems a lot of money. That's not my problem as the vouchers will cover the full cost and DCMS has authorised the project to proceed. I just want the work completed.
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 15:50:07
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
Thanks for sharing that, I was surprised to hear that it would be 4x as much to add 33 additional properties but not knowing the geography of your area its hard to understand the extra work involved. A few years ago I helped with a CFP and the cost actually went down when adding extra properties as the cost to add those properties was less that the extra contribution from Openreach, I appreciate every CFP is different and if you can cover the cost with vouchers its happy days for all those benefiting from it smile

Edited by dect (Tue 12-Jan-21 16:01:46)

Standard User chriswillsher
(learned) Tue 12-Jan-21 16:08:06
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Re: How does splicing / splitting work?


[re: shortshrift27] [link to this post]
 
I don't really know what I am talking about. I only said "secondary" as there has been some discussion elsewhere in this thread if what we have in the ground is a splitter or an aggregation node.
This should show a picture of what is on some of the poles. As I understand it from information on the web this could be a DP, or a splitter or a splitter/DP or a transition joint.

https://i.postimg.cc/DZz4BvN0/IMG-4862.jpg
Standard User witchunt
(experienced) Tue 12-Jan-21 16:53:12
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
I thinks is a Fibre DP
Standard User dect
(fountain of knowledge) Tue 12-Jan-21 17:22:10
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Re: How does splicing / splitting work?


[re: witchunt] [link to this post]
 
In reply to a post by witchunt:
I thinks is a Fibre DP
Thats in line with what Zarjaz told the OP regarding that pic on 14th July 2020


Edit: he also told the OP that below is a blown fibre node, possibly a splitter.
In reply to a post by chriswillsher:
Better quality image - I hope

Edited by dect (Tue 12-Jan-21 17:26:14)

Standard User witchunt
(experienced) Tue 12-Jan-21 17:33:18
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
I wont argue with that!
Standard User Pheasant
(committed) Tue 12-Jan-21 18:27:34
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Re: How does splicing / splitting work?


[re: MrSaffron] [link to this post]
 
In reply to a post by MrSaffron:
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.

Indeed. The only time they would 'splice' a submarine cable was if it sustained damag (storm, anchor drag etc) or one the in-line amps needed maintenance. Even then they have loads of redundancy, as getting a cable ship out to fix is a tad more expensive than a couple of blokes from Kelly or Morrison in a white van packing a Type-72C under their arm wink
Standard User jabuzzard
(experienced) Tue 12-Jan-21 18:36:45
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Re: How does splicing / splitting work?


[re: Pheasant] [link to this post]
 
Wrong they splice submarine cables for additional drop points.

I randomly caught a TV show on Quest once where they where doing it. The cable was live and continuously transmitting data on the other fibres while they hauled it up from the ocean floor, cut into the armoured cable and spliced the new drop cable in, then sealed it all back up and lowered it to the bottom of the ocean again.

Sure in a different league than on land, but then one could reasonably conclude it's a lot easier and cheaper to do on land. For starters you don't need a crewed ocean going vessel that costs hundreds of millions to buy and run.
Standard User Pheasant
(committed) Tue 12-Jan-21 18:40:26
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Re: How does splicing / splitting work?


[re: jabuzzard] [link to this post]
 
In reply to a post by jabuzzard:
Wrong they splice submarine cables for additional drop points.

I randomly caught a TV show on Quest once where they where doing it. The cable was live and continuously transmitting data on the other fibres while they hauled it up from the ocean floor, cut into the armoured cable and spliced the new drop cable in, then sealed it all back up and lowered it to the bottom of the ocean again.

Sure in a different league than on land, but then one could reasonably conclude it's a lot easier and cheaper to do on land. For starters you don't need a crewed ocean going vessel that costs hundreds of millions to buy and run.

Depends on the link Mr Buzzard. Some are straight point to point and others are multi-point.
Standard User weesteev
(newbie) Tue 12-Jan-21 21:45:13
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
Hi Chris

I live not far from you (just South of Kinross). I would be happy to drop by the area some time and show you the openreach maps for the region and walk you through the infrastructure if that would help? Drop me a PM and we can catch up sometime.

Cheers

Although I work for Virgin Media, all comments are a personal opinion and not a direct expression of my employer wink
Standard User Zarjaz
(eat-sleep-adslguide) Tue 12-Jan-21 21:49:59
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
Those aren’t ‘secondary splitters’ they are just ‘track nodes’ a network joint.

In the current GPON set up there is only ever one splitter node.

Standard User Fastman3
(member) Tue 12-Jan-21 22:02:25
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Re: How does splicing / splitting work?


[re: chriswillsher] [link to this post]
 
thos premsises will likley be left with a joint probably provided as par of your build as it will have passed them on the way (lit is likely that this will cost them significantly more per premise if and when they realise that the fibre is outside there premise but the scheme has missed them that the average cost per premise on your overall scheme
Standard User Fastman3
(member) Tue 12-Jan-21 22:08:36
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
Dect - CFPs are determined by the network build and the premises required , how the premises to be served all of these could affect the gap requried by community the bigger the network build and the smaller amount of premises the greater the gap will be, , all of these are determined by their individual circumstances and specifics (and also whether the premises have access to a superfast service (FTTC) and where you have to get back to a Headend as well
Standard User MaryHinge
(member) Sun 17-Jan-21 11:07:47
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Re: How does splicing / splitting work?


[re: Woolwich] [link to this post]
 
Based on what I've observed locally it appears they typically run a 36 or 72 mini fibre cable (from the AG node or intermediate DP?) to a chain of splitter nodes. The 36 / 72 fibres in the cable are grouped in bundles of 12 individual fibres.

I'm not sure but my assumption is that at each SPN they break into one of the bundles of 12 fibres and the rest just pass straight through to the next SPN, so a 36 fibre cable would support a chain of 3 SPNs, and a 72 would support a chain of 6 SPNs.

Of course each SPN would not likely need all 12 individual fibres as the ones I've seen take a maximum of 4 individual 32-way splitters (= max 128 CBT ports per SPN) so you would only need 4 fibres per SPN, but the remaining fibres from the bundle of 12 are stored for future (non-GPON?) use.

Interestingly it seems that the splitter devices I've seen may actually have two input fibres, the limited research I've done suggests that this can be used to provide active/passive redundancy from two separate OLTs but I'm I assume Openreach would bother with this for a consumer-grade product, especially as if you wanted more useful redundancy you'd ideally want geographically-separate fibre paths to two different headend exchanges.

Anyway all of the above could be completely wrong as it's just based on visual observations rather than speaking to anyone familiar with the deployment.
Standard User dect
(fountain of knowledge) Sun 17-Jan-21 22:28:01
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Re: How does splicing / splitting work?


[re: MaryHinge] [link to this post]
 
In reply to a post by MaryHinge:
it seems that the splitter devices I've seen may actually have two input fibres
No one I can recall on here has ever suggested a 32 way PON splitter has the capability of 2 input fibres.

Edited by dect (Mon 18-Jan-21 09:48:09)

Standard User MaryHinge
(member) Mon 18-Jan-21 13:47:03
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Re: How does splicing / splitting work?


[re: dect] [link to this post]
 
No one I can recall on here has ever suggested a 32 way PON splitter has the capability of 2 input fibres.


Here are some examples of dual-input splitters:

Table on page 2 lists 2x4, 2x8, 2x16, 2x32

eBay listing of the sort of dual-input splitter I've observed in use by Openreach locally

Description of a dual-input GPON splitter

The optical splitter with 2x64 split configurations is a little bit more complicated than the 1x4 split configurations. There are two input terminals and sixty-four output terminals in the optical splitter in 2x64 split configurations. Its function is to split two incident light beams from two individual input fiber cables into sixty-four light beams and transmit them through sixty-four light individual output fiber cables.


Thinking about it logically if I'm right and they are using dual input splitters then the second input could feasibly be for other wavelengths e.g. from an XGS-PON OLT?
Standard User ft247
(newbie) Mon 18-Jan-21 14:01:10
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Re: How does splicing / splitting work?


[re: MaryHinge] [link to this post]
 
In reply to a post by MaryHinge:
Thinking about it logically if I'm right and they are using dual input splitters then the second input could feasibly be for other wavelengths e.g. from an XGS-PON OLT?


I'm not sure (note - I do not have any PON design experience) that's the way to do things.

Multiplexing GPON and XGS-PON is possible as they use different wavelengths - but I would say that should be achieved at the exchange using WDM kit, which diverts as much of the wavelength of interest as possible to each OLT, rather than wasting half of the GPON signal by sending it to the XGS-PON OLT and vv.

I'd be very interested to see the design rationale for trading half the optical budget for a redundant fibre core, given that the second fibre is unlikely to take a diverse route.
Standard User Pheasant
(committed) Mon 18-Jan-21 16:22:46
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
I'd be very interested to see the design rationale for trading half the optical budget for a redundant fibre core, given that the second fibre is unlikely to take a diverse route.

Not sure I follow. How do you figure that you trade "half the optical budget for a redundant fibre core"?

The OR optical budget for GPON is in the order of 28 dB between OLT and ONT.

The IL difference between a 1.x and a 2.x splitter is between 0.3dB and 0.8 dB according to the Prysmian data sheet link above

My Broadband Speed Test
Standard User ft247
(newbie) Mon 18-Jan-21 17:05:52
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Re: How does splicing / splitting work?


[re: Pheasant] [link to this post]
 
In reply to a post by Pheasant:
Not sure I follow. How do you figure that you trade "half the optical budget for a redundant fibre core"?

The IL difference between a 1.x and a 2.x splitter is between 0.3dB and 0.8 dB according to the Prysmian data sheet link above


I should have said "3dB of optical budget on the upstream", but on further reading I am clearly misunderstanding something, at least in the upstream direction.

I was thinking that for a signal passing upstream from ONT, when it reaches the splitter that upstream signal is now split two ways rather than one, which would imply 3dB extra loss.

Optically it makes sense that in the downstream direction there is <1dB extra loss, but how can that hold for the upstream?
Standard User candlerb
(fountain of knowledge) Mon 18-Jan-21 17:07:52
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
Multiplexing GPON and XGS-PON is possible as they use different wavelengths - but I would say that should be achieved at the exchange using WDM kit


Indeed, I believe that's what is done. It's easy to manage as it's all done exchange-side; and it avoids having to allocate a second fibre all the way to every splitter.

Insertion loss is also a consideration. Think about the light coming from an end-user ONT; if it were split 50/50 between two splitter legs then that's a minimum 3dB loss. That's not "half the optical budget", but it's still a significant loss.
Standard User Pheasant
(committed) Mon 18-Jan-21 17:19:22
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
In reply to a post by Pheasant:
Not sure I follow. How do you figure that you trade "half the optical budget for a redundant fibre core"?

The IL difference between a 1.x and a 2.x splitter is between 0.3dB and 0.8 dB according to the Prysmian data sheet link above


I should have said "3dB of optical budget on the upstream", but on further reading I am clearly misunderstanding something, at least in the upstream direction.

I was thinking that for a signal passing upstream from ONT, when it reaches the splitter that upstream signal is now split two ways rather than one, which would imply 3dB extra loss.

Optically it makes sense that in the downstream direction there is <1dB extra loss, but how can that hold for the upstream?

This might help...

https://info.support.huawei.com/AccessInfoTool/PON_B...

My Broadband Speed Test
Standard User Pheasant
(committed) Mon 18-Jan-21 18:16:31
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
In reply to a post by candlerb:
In reply to a post by ft247:
Multiplexing GPON and XGS-PON is possible as they use different wavelengths - but I would say that should be achieved at the exchange using WDM kit


Indeed, I believe that's what is done. It's easy to manage as it's all done exchange-side; and it avoids having to allocate a second fibre all the way to every splitter.

Insertion loss is also a consideration. Think about the light coming from an end-user ONT; if it were split 50/50 between two splitter legs then that's a minimum 3dB loss. That's not "half the optical budget", but it's still a significant loss.

Yes. At the headend they could combine the output of the respective OLT wavelength (1490/1310 for GPON and 1577/1270 for XGS) using a pretty basic planar FWDM and take the common output to the PON.

My Broadband Speed Test
Standard User ft247
(newbie) Mon 18-Jan-21 19:05:14
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Re: How does splicing / splitting work?


[re: Pheasant] [link to this post]
 
In reply to a post by Pheasant:
This might help...

https://info.support.huawei.com/AccessInfoTool/PON_B...


And very interesting it is - I can see a ~0.8dB increase in downstream attenuation changing the 1:n splitter to a 2:n splitter.

What I still can't get my head around is how the upstream path doesn't take a >3dB loss changing from a 1:n to a 2:n.
Standard User j0hn83
(fountain of knowledge) Tue 19-Jan-21 05:34:52
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Re: How does splicing / splitting work?


[re: MaryHinge] [link to this post]
 
In reply to a post by MaryHinge:
Thinking about it logically if I'm right and they are using dual input splitters then the second input could feasibly be for other wavelengths e.g. from an XGS-PON OLT?


Each splitter has a single lit fibre connected.

OpenReach use this single fibre to carry both the GPON and XGS-PON signal.
No need for a 2nd fibre or 2nd input to do this.

As you pointed out yourself OpenReach don't have the OLT port capacity available for splitters to have a backup fibre connected.
Standard User MaryHinge
(member) Tue 19-Jan-21 08:07:25
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Re: How does splicing / splitting work?


[re: j0hn83] [link to this post]
 
Each splitter has a single lit fibre connected.

OpenReach use this single fibre to carry both the GPON and XGS-PON signal.
No need for a 2nd fibre or 2nd input to do this.

As you pointed out yourself OpenReach don't have the OLT port capacity available for splitters to have a backup fibre connected.


@John83 since you seem to be familiar with this would you be able to confirm if this part of my original post is correct?

I'm not sure but my assumption is that at each SPN they break into one of the bundles of 12 fibres and the rest just pass straight through to the next SPN, so a 36 fibre cable would support a chain of 3 SPNs, and a 72 would support a chain of 6 SPNs.

Of course each SPN would not likely need all 12 individual fibres as the ones I've seen take a maximum of 4 individual 32-way splitters (= max 128 CBT ports per SPN) so you would only need 4 fibres per SPN, but the remaining fibres from the bundle of 12 are stored for future (non-GPON?) use.
Standard User Pheasant
(committed) Tue 19-Jan-21 12:06:47
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
In reply to a post by Pheasant:
This might help...

https://info.support.huawei.com/AccessInfoTool/PON_B...


And very interesting it is - I can see a ~0.8dB increase in downstream attenuation changing the 1:n splitter to a 2:n splitter.

What I still can't get my head around is how the upstream path doesn't take a >3dB loss changing from a 1:n to a 2:n.

Have a look at the physics of passive optical splitters here:
https://www.physics-and-radio-electronics.com/blog/f...

Insertion Loss for passive splitters goes up logarithmically based on the number of *output* ports. Forward and return losses are near enough identical - looking at the Huawei PON budget calculator above, there is only a small difference in optical loss between down stream and upstream. This difference accounted by the change in downstream and upstream optical wavelengths - just as it would be if you were measuring loss on a single piece of fibre.

The actual difference in IL between a 1:n splitter and 2:n splitter should (in theory) be no more than 0.2 dB. The loss curve is effectively the same, being driven by the number of outputs, just shifted slightly. I just plugged some numbers into the budget calculator above and it predicted an overall end-to-end 0.3dB difference in loss budget swapping (both forward and reverse) between a 1:4 splitter and 2:4 splitter. So hardly anything.

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Standard User j0hn83
(fountain of knowledge) Tue 19-Jan-21 12:11:38
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Re: How does splicing / splitting work?


[re: MaryHinge] [link to this post]
 
I've no idea how many fibres are in each fibre tube that goes to the Splitters.

On my development they pulled a single fibre tube (containing who knows how many fibres) to each jointbox containing a splitter.
They put 2 x 32 Splitters in each jointbox they pulled the fibre to.

Some images of the Prysmian outdoor plant used by OpenReach...

https://ibb.co/0qDTdYS

Edited by j0hn83 (Tue 19-Jan-21 12:11:58)

Standard User ft247
(newbie) Tue 19-Jan-21 19:49:38
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Re: How does splicing / splitting work?


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
Some images of the Prysmian outdoor plant used by OpenReach...

https://ibb.co/0qDTdYS


Very interesting, thanks. The yellow joint is marked as GPON + FIRS. FIRS presumably stands for Fibre Integrated Reception System, which I didn't think would be of interest to Openreach.
Standard User j0hn83
(fountain of knowledge) Tue 19-Jan-21 19:52:32
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
In reply to a post by j0hn83:
Some images of the Prysmian outdoor plant used by OpenReach...

https://ibb.co/0qDTdYS


Very interesting, thanks. The yellow joint is marked as GPON + FIRS. FIRS presumably stands for Fibre Integrated Reception System, which I didn't think would be of interest to Openreach.


It isn't.
I should have said some of the plant used by OpenReach.
Standard User ft247
(learned) Tue 19-Jan-21 21:12:12
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Re: How does splicing / splitting work?


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
It isn't.
I should have said some of the plant used by OpenReach.


There was an Openreach FIRS product once - withdrawn in late 2019. It's visible in their price list section 5.1.2.

Edited by ft247 (Tue 19-Jan-21 21:14:06)

Standard User j0hn83
(fountain of knowledge) Tue 19-Jan-21 23:34:59
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
Never spotted that. Interesting.

I've uploaded the Prysmian document those images came from:

https://drive.google.com/file/d/13ZL5jbyzAOT4g1WXfVq...

Edited by j0hn83 (Tue 19-Jan-21 23:54:58)

Standard User Pheasant
(committed) Wed 20-Jan-21 14:04:16
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Re: How does splicing / splitting work?


[re: ft247] [link to this post]
 
In reply to a post by ft247:
In reply to a post by j0hn83:
It isn't.
I should have said some of the plant used by OpenReach.


There was an Openreach FIRS product once - withdrawn in late 2019. It's visible in their price list section 5.1.2.

Interesting. Probably was quite niche and not many takers. Looks like IRS still could've happily worked (@1550nm) alongside GPON and even future XGSPON.

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Standard User Pheasant
(committed) Sun 24-Jan-21 09:06:52
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Re: How does splicing / splitting work?


[re: candlerb] [link to this post]
 
In reply to a post by candlerb:
In reply to a post by ft247:
Multiplexing GPON and XGS-PON is possible as they use different wavelengths - but I would say that should be achieved at the exchange using WDM kit


Indeed, I believe that's what is done. It's easy to manage as it's all done exchange-side; and it avoids having to allocate a second fibre all the way to every splitter.

Insertion loss is also a consideration. Think about the light coming from an end-user ONT; if it were split 50/50 between two splitter legs then that's a minimum 3dB loss. That's not "half the optical budget", but it's still a significant loss.

Had a look online and Huawei do make ‘CSHD’ 8-port and ‘CSHF’ 16-port OLT line cards for their MA5800 series OLT that are GPON/XGSPON capable on all cages.

There are corresponding combo SFP+ modules (from HiSilicon the Huawei in-house silicon fab) that have parallel GPON and XGSPON interfaces and the FWDM built into the SFP+ package for all four wavengths.

http://www.o.hisilicon.com/-/media/HisOe/Products/Pr...

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