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Author Topic: Long distance fibre  (Read 1593 times)

CarlT

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Re: Long distance fibre
« Reply #15 on: January 07, 2020, 01:00:37 AM »

Sorry, last thought.

Remember also that the fibre runs will be very indirect. They'll stop off at a bunch of places to drop off traffic or be regenerated.

The coaxial stuff needed frequent amplification and fibre following those routes will stop off plenty, even if it's just to go through a patch panel rather than being regenerated.

Plenty of options to take diversions along duct paths, too. For historic reasons there is a lot of resilience on the BT network: UKWMO used it as did the WBxxxx siren warning transmission systems.
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Weaver

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Re: Long distance fibre
« Reply #16 on: January 07, 2020, 06:43:52 AM »

Would you always use roads or railways rather than going through the middle of nowhere? Because of the hassle of securing permission from farmers so very many times? Roads can be very wiggly, so a long distance route could get longer than the straight line route.

What else is there ? Canals? Long distance big pipelines - is that correct?

I thought I remembered something about B4RN and a pipeline giving them a huge backbone when they got started, but I canít find it so I must be imagining things.

If youíre in the middle of nowhere though like B4RN you might get lucky and they have the M6 so theyíre extremely lucky.

I was reading about Bogons the ISP and their Cold War bunker in Perthshire. They needed a fibre optic massive link to Edinburgh and Openreach hooked Bogons up with a 100Gbps link. I would love to know just exactly how that was physically done. Existing ducts? Upgrades of existing paths?

ó
The train lines I suppose can be a great asset, accessible and straight, so the shortest distance, and therefore they minimise latency.

If you need to switch sides, or you have a problem because there is a line branching off on your side, then you have to go under the track.

In the latter case, will there often be an existing (speculative) duct in place ready, just for this purpose ?

If no existing duct, can we easily just sneak under, by scooping out a little material under the rail and then replacing some of it as needed?

Can you buy the rights to put your own fibre into the railway line?
« Last Edit: January 07, 2020, 11:15:47 AM by Weaver »
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CarlT

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Re: Long distance fibre
« Reply #17 on: January 07, 2020, 10:36:40 AM »

Would you always use roads or railways rather than going through the middle of nowhere? Because of the hassle of securing permission from farmers so very many times? Roads can be very wiggly, so a long distance route could get longer than the straight line route.

What else is there ? Canals? Long distance big pipelines - is that correct?

Canals are largely already done and Sky now own that network via Easynet, who in turn purchased Fibreway.

Openreach usually avoid going across private land like the plague - wayleaves are an ass unless you're B4RN and can blag them for free :)

A reminder also you'll need to get access both to install and to repair where necessary, so keeping this stuff reasonably close to roads is useful. There will be occasions where the fibre goes on poles and takes a bit of a weird route.

I was reading about Bogons the ISP and their Cold War bunker in Perthshire. They needed a [url[http://comriedevelopmenttrust.org.uk/big-bandwidth-at-the-bunker]fibre optic massive link to Edinburgh[/url] and Openreach hooked Bogons up with a 100Gbps link. I would love to know just exactly how that was physically done. Existing ducts? Upgrades of existing paths?

Existing duct / paths, some new fibre and some new digging. Any and all of the above - Excess Construction Charges are there for a reason  :)

The train lines I suppose can be a great asset, accessible and straight, so the shortest distance, and therefore they minimise latency.

If you need to switch sides, or you have a problem because there is a line branching off on your side, then you have to go under the track.

In the latter case, will there often be an existing (speculative) duct in place ready, just for this purpose ?

If no existing duct, can we easily just sneak under, by scooping out a little material under the rail and then replacing some of it as needed?

Can you buy the rights to put your own fibre into the railway line?

I'm not that familiar with the train lines beyond that Network Rail can be a real pain to deal with and there is an extensive fibre network running alongside them. This was sold off alongside the railways. I was, however, wrong about who owned them - it's actually Level 3 on the core and Thales on the other stuff.

The terms and conditions of this arrangement I'm not aware of, neither am I aware of what would be required to cross them. There are certainly ducts there though you'd need to lease space in them. To go underneath them you'd be looking at directional drilling and it would be incredibly expensive.
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Black Sheep

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Re: Long distance fibre
« Reply #18 on: January 07, 2020, 05:38:29 PM »

Planning FTTP,  for the vast majority of the time, follows the same route its Cu/Ali cousins take.

As Carl points out, there are a plethora of innovations available to use to avoid disruption and also mentions the retrospective access to the network for repairs, which is why Aggs/Spliiters/CBT are planned the best they can be to be sited in easily accessible boxes (rather than carriageway boxes, or anywhere TM - traffic Management - may be needed).

Please also bear in mind, the books are constantly being re-written with regard to FTTP deployment as innovations get better all the time, government backing also gets bigger (especially where wayleaves and MDU's are concerned), and of course its is  a relatively 'new product' for all concerned ....

 

 
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Weaver

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Re: Long distance fibre
« Reply #19 on: January 07, 2020, 10:42:55 PM »

Iíve been reading and horizontal drilling and trenchless in general. Fascinating stuff. Iím very interesting in the drillhead location tech stuff. I donít know though how you close the last bit of distance when you know roughly where your two ends are but youíre not close enough. And I donít know how you know when your ends have met up. Iíd like to know a lot more about exactly how all that is done.

Actually, Iíve just realised: perhaps you only have one end, and you locate that then drill straight down to it, but that means that you have not halved the maximum distance that you can cross, you donít have two mutually meeting halves, ie two mutually meeting drill lengths, meeting under the road or whatever it is youíre trying to pass underneath of. That solves the problem of locating two ends, by only having one Ďendí.

ó
A thought: Carl was talking about Fibreway on canal towpaths. That ought to make them exceptionally reliable, no? Because there will be pretty much zero problems with other minidigger men and women wrecking your fibre with their alien works. Does that sound plausible?

I read an article about Fibreway from 1994 [!] - pretty much the Big Bang as far as internet history is concerned.
« Last Edit: January 07, 2020, 11:12:24 PM by Weaver »
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licquorice

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Re: Long distance fibre
« Reply #20 on: January 08, 2020, 08:46:20 AM »

You have to remember that FTTP distribution fibre and core network fibre are 2 entirely different animals.

In days gone by, there were effectively 3 (or 4 if you differentiate between cabinet E side and D side cables) levels of cable distribution.

Local network from the exchange to individual premises via cabinets and DPs, Junction cables linking local exchanges to a larger switching centre and Trunk cables linking major switching centres.

The Trunk and Junction network would have been ducted and followed roads closely and that duct network will still be used today for the fibre core network.
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Weaver

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Re: Long distance fibre
« Reply #21 on: January 08, 2020, 09:18:53 AM »

If you have an existing duct, how do you upgrade link capacity? You pray to the gods that you can cram more fibres into it, but the gods donít hear you and the duct is really really full. Can you try and cram more wavelengths down the fibres that you already have?

Does it ever happen that you remove some rubbish fibre to free up the duct and put in better fibre instead?
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licquorice

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Re: Long distance fibre
« Reply #22 on: January 08, 2020, 02:19:31 PM »

For ex Trunk and Junction routes, if the old copper cables have been removed, there will be ample duct room. The cables will be multi fibre which may not all be lit and extra wavelengths can be utilised in DWDM systems. I'm not sure what current technology offers (possibly 16Tb/s) but when I retired 12 years ago the core network cables were capable of carrying around 2Tb/s per fibre.
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Black Sheep

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Re: Long distance fibre
« Reply #23 on: January 08, 2020, 05:43:06 PM »

For ex Trunk and Junction routes, if the old copper cables have been removed, there will be ample duct room. The cables will be multi fibre which may not all be lit and extra wavelengths can be utilised in DWDM systems. I'm not sure what current technology offers (possibly 16Tb/s) but when I retired 12 years ago the core network cables were capable of carrying around 2Tb/s per fibre.

I've had a very quick search that mentions in June 2017 they managed 13 terabits per second over a single fibre, on a live 250mile round trip circuit.

It could well be more now, as you say Licq ??  :)
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Weaver

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Re: Long distance fibre
« Reply #24 on: January 08, 2020, 05:50:46 PM »

Woa - 2Tb/s will keep you going. Isnít that roughly about the half of LINX or LONAP peak traffic?
« Last Edit: January 08, 2020, 05:58:04 PM by Weaver »
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Weaver

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Re: Long distance fibre
« Reply #25 on: January 09, 2020, 04:23:48 AM »

So capacity isnít the problem, itís about reaching people. And these service providers have no excuse for congestion unless the nodes are the bottlenecks not the links.

Thanks to Licquorice for that. And hello my friend, nice to hear from you, feels like I havenít heard from you in a while. Hope you are doing well.
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CarlT

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Re: Long distance fibre
« Reply #26 on: January 11, 2020, 11:34:27 AM »

The access fibre is something of a PITA. Often you're using a single fibre to serve a single premises. This was part of the issue when Virgin Media's high fibre count access network cables were pile driven outside their New Malden site.

The trunks you can push more down the same wavelengths by using analogue transmission, and can get better efficiency out of the fibre by using different Wavelength Selectable Switches. Remember these wavelengths have to go to something to terminate them, prisms can bounce them around but they have to hit something to decode them. WSS select wavelengths and deliver them to receivers. Can only demodulate so much via a single transceiver so have to split the 'big' signals for optical to electrical conversion and combine them for electrical to optical. :)

Older school 'on or off' optics are old news. Optics now run with 2 sine waves in quadrature, one in phase one 90 degrees out of phase, and by measuring power variance between them Quadrature Amplitude Modulation can be used to further increase density. They emulate the electrical version of combining two electrical signals using optical inferometers.

We can now get 400 Gb/s out of 75 GHz of optical spectrum via 64QAM. 256QAM, increasing throughput in the same optical spectrum by another third, is being tested.
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Weaver

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Re: Long distance fibre
« Reply #27 on: January 12, 2020, 12:07:13 PM »

I donít know anything at all about optical comms, I would like to read up on it. Iím familiar with all the standard electrical modulation schemes and the maths behind them. I didnít know that optics had now reached the sophistication of going beyond 1-bit/off-on as you said and going to quadrature and QAMn. Of course electrical does more still for the moment with QAM1024 and even QAM4096 I saw mentioned in connection with microwave comes (how on Earth? Never mind.).

400Gb/s out of 75GHz, so what 5.3 bits/Hz ? Is that good these days by RF standards?
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CarlT

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Re: Long distance fibre
« Reply #28 on: January 12, 2020, 02:09:21 PM »

It's equivalent of 64 QAM. Nothing special, your ADSL will be managing more that that on some tones.

More impressive is it being emulated by optical inferometers.

EDIT: A reminder that you can find 15 bits per tone on DSL - 32768 QAM.
« Last Edit: January 12, 2020, 02:11:45 PM by CarlT »
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Weaver

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Re: Long distance fibre
« Reply #29 on: January 13, 2020, 08:07:45 PM »

Good point, I had forgotten to count my DSL configurations.
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