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Author Topic: Long distance fibre  (Read 529 times)

Weaver

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Long distance fibre
« on: September 20, 2019, 10:37:52 PM »

[Apologies sincerely if I have asked this before; it’s been bugging me for a long time but I can’t remember whether or not I have already actually come out and asked anyone ]

How does a fibre link get to wherever - either Inverness or Fort William - civilisation anyway - from NSBFD the Broadford or Kyle exchange ? It’s 82 or 87 miles respectively by road. Can it be done in one hop ?

And if not what do they do then ? Have to find a location somewhere where there is power available locally, for active repeater kit ? Or send power down the cable ? Or even generate power at some intermediate node, by solar and wind combined, or something ?
« Last Edit: September 21, 2019, 12:17:17 AM by burakkucat »
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burakkucat

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Re: Long distance fibre
« Reply #1 on: September 21, 2019, 12:45:39 AM »

Interesting question.

Obviously I can't "speak" for Beattie Bellman but I wouldn't be surprised if one of her "escapees" could provide some distance figures, for single mode fibre.

Then, of course, we have CarlT who, I'm sure, would also be able to give some typical distances for the various types of fibres.

A quick search finds a table by the supplier Universal Networks.

Looking at the Submarine Cable Map and considering, say, TAT-14 I wonder how that 15,295 km is covered? I read --

Quote
The cable system is comprised of four fiber (sic) pairs and traffic can be configured point to point or in (protected) ring configuration.

TAT-14 has a total design capacity of 9.38Tb/s.
TAT-14 has a total system (lit) capacity of 3.15Tb/s.

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Weaver

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Re: Long distance fibre
« Reply #2 on: September 21, 2019, 01:02:07 AM »

That is an active cable ? It has power sent down it to active inline repeaters ?

I wonder what the limit is without any repeaters.

And I wonder which type is used on land in the highlands. In the BT undersea cable laying orgy between islands a couple of years back, the chap from BT who gave a lecture about the project said that it was exclusively passive cable. The reason behind that decision was he said safety; they were worried about a fisherman hooking the cable, lifting it up and getting a jolt of god knows how many volts for his trouble iirc. I presume passive cable is cheaper too, obviously, but I don’t know how much. Presumably they could get away with it in that project because none of the inter-island distances are that great. It’s not that far from Skye to Uibhist or to Harris, and that has to be the longest hop that they had to deal with in that project. Mind you I don’t know about Orkney to Shetland which might well be via Fair Isle which would halve the link and thus halve the problem. I don’t know how undersea cables get to Shetland; I don’t even know if the cable path comes from Orkney, which would be the same route, or whether it comes directly from mainland Britain.
« Last Edit: September 21, 2019, 01:32:42 AM by Weaver »
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burakkucat

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Re: Long distance fibre
« Reply #3 on: September 21, 2019, 01:18:26 AM »

Looking at the table, mentioned above, we see --



I think 100 km is about 62.5 miles and 40 km is about 25 miles. Hmm . . . I'm intrigued.

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Weaver

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Re: Long distance fibre
« Reply #4 on: September 21, 2019, 01:36:13 AM »

Distances:

Orkney to Shetland :
49 mi direct from Orkney (North Ronaldsay) to Shetland
27 mi from Orkney (North Ronaldsay) to Fair Isle mid-point
24 mi from mid-point (Fair Isle) to Shetland

15 mi from Skye to Western Isles (to either Harris or to Uibhist)

So 15 mi must be ok for passive but I don’t know about the 27 mi hop to Fair Isle or the 49 mi hop Orkney to Shetland direct. From Burakkucat’s table 40 km is 24.85 mi and so even the shortest of the latter hops is out. It seems that Fair Isle even will not be enough to help. And Skye to Inverness or Fort William means big trouble too.



As for Skye to Inverness or Fort William :

Broadford (Skye) to Inbhir Garadh in the Great Glen would be one possible midpoint but that is still 57 mi and so no good for a 40km limit. Would need additional hops. And there’s the rest of the run, either 23 mi up the Great Glen from Inbhir Mhoireastain by Loch Ness into Inverness itself or 25 mi down the Great Glen into Fort William. So these two latter ‘halves’ might be just about ok.

The solution would have to be a node at the Cluanaidh Inn, which is in the middle of nowhere, on the main A87 road, has mains of course and is about 21 mi from the Great Glen as the crow flies so even that is pushing it for a 40km limit as the road distance will be somewhat greater.
« Last Edit: September 21, 2019, 02:13:59 AM by Weaver »
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burakkucat

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Re: Long distance fibre
« Reply #5 on: September 21, 2019, 02:09:25 AM »

Seeing "Inbhir Garadh" had me scratching my head. Then I had a sudden thought - Google Maps will know. And it showed me Invergarry:)
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Weaver

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Re: Long distance fibre
« Reply #6 on: September 21, 2019, 02:31:17 AM »

That place has various forms and I’m unsure a to which is to be preferred as I haven’t met any local speakers from the area. Inbhir Gàraidh or Inbhir Gearraidh and a medley of possibilities derived from these provide yet more alternatives. Speakers could have been confused by similar words gàradh ‘dike’, ‘garden’ and gearradh ‘cut’, ‘cutting’ from the verb for cut, also ‘summer grazing place for cattle’. The former has a long vowel. The latter has an initial /gj/-like sound. There is also a possible choice between genitive singular and genitive plural forms. Combine all the lot together and the range of possibilities is daunting.
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Weaver

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Re: Long distance fibre
« Reply #7 on: September 21, 2019, 03:00:09 AM »

For some reason, unlike in Wales which has a much better track record with maps, maps of Scotland tend to still show anglicised forms on the mainland whose mangling makes placenames hard to decipher. Some maps are doing rather better in the Western Isles but have yet to get their act together on the mainland and in Skye. Many many obvious mistakes, misspellings and grammatical errors abound which would not be found in Wales and no maps of England would dare exhibit misspellings such as ‘*Burminghum’. Recently the authorities aided by the Scottish Placename Society, of which I am a member, and other bodies have done a good job getting all the road signs fixed but trying to sort out all the various maps is a Herculean task.

In many parts of the country the placenames are Norse (Old Norwegian) mangled by Gaelic speakers or from British (ie Welsh), not Gaelic and some have been ‘gaelicised’ in spelling. For these names it seems anything goes but now the tendency is to increasingly spell these names with phonetic Gaelic spelling based on the pronunciation of local Gaelic speakers, which is a sensible choice.

English speaking readers have to cope with the complex coding system which Scottish Gaelic and Irish use to encode far too many consonants into the few symbols provided by the Latin alphabet. Welsh does not have this problem because it has only approximately half as many consonants. The letter h after a consonant can be present or absent and one of two sets of extra vowels are used to bracket consonants - the sets are a/o/u and e/i, one or the other - and this choice between the two sets, combined with the +/- h option gives four possible consonant sounds per core consonant letter. To prevent ambiguity the vowels on either side of any consonant must be from the same set.
Vowels can be short or long and in traditional Gaelic spelling there can be à ì ù and è ò | é ó, the accents are used to mark long vowels and the choice of grave vs acute for e or o gives different sounds. So the number is sounds is massive, Gaelic spelling is a code, and like utf-8 it needs decoding first; in the code, multiple letters convert into single sounds. Compare English mac and mace where the addition of the silent e changes the consonant and the vowel. The difficulty for an English-speaking audience perhaps explains some of the differences in historical map-making practice between Wales and Scotland.
« Last Edit: September 21, 2019, 01:42:18 PM by Weaver »
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CarlT

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Re: Long distance fibre
« Reply #8 on: September 21, 2019, 08:57:23 AM »

You can get between 80 and 120 km out of a 10GBASE-ZX optical link.

That's just a basic SFP you plug into a router or switch. If you put 'real' transmission equipment either side you can get reach of over 400 km without amplification, regeneration or using anything experimental depending how many wavelengths you need the fibre to carry.
« Last Edit: September 21, 2019, 09:15:58 AM by CarlT »
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Weaver

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Re: Long distance fibre
« Reply #9 on: September 21, 2019, 01:31:23 PM »

That answers my questions then. With 400km there’s no issue anywhere. Thank you for that Carl.

I wonder if there are any maps around showing large network operators’ geography in Britain ?
« Last Edit: September 21, 2019, 01:47:27 PM by Weaver »
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CarlT

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Re: Long distance fibre
« Reply #10 on: September 21, 2019, 02:32:25 PM »

https://www.telecomramblings.com/network-maps/europe/

Out of date. BT's full network map is I suspect not just a company confidential thing but also a matter of national security.
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j0hn

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Re: Long distance fibre
« Reply #11 on: September 21, 2019, 02:44:28 PM »

Is this the sort of thing you're looking for?
« Last Edit: September 21, 2019, 02:46:40 PM by j0hn »
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Weaver

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Re: Long distance fibre
« Reply #12 on: September 21, 2019, 03:21:30 PM »

@CarlT good point. A shame though as academic researchers could benefit from this kind of info for research purposes; would give them a concrete basis for modelling.

@j0hn brilliant thank you very much indeed. Was that from the time of the undersea cabling project a couple of years ago? I should have remembered that that might be a likely source of maps but I forgot that the maps included on-land links, which they very likely upgraded hugely; the run right up the west coast including the likes of Geàrrloch in Wester Ross and settlements much further north up towards cape wrath and along the north coast even, to complete a ring heading towards hops across to Orkney.

BT did a superb job, including a hop across the sea from Skye to Malaig which has the benefit of a very short run to Fort William, ensures Malaig isn’t left out, and improves triangulation redundancy for Skye. My missus suggested that Malaig might be a route for BT from Skye to Fort William rather than trying to go from the Skye Bridge to the Great Glen.



Any one have a similar map for England ?
« Last Edit: September 21, 2019, 03:25:23 PM by Weaver »
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