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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)


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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

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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
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