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[waltergmw]

Gentlefolk,

This might interest some before reading the full report.

Kind regards,
Walter

http://br0kent3l3ph0n3.wordpress.com/2012/07/30/lords-slam-governments-strategy-free-broadband-plan/

[kitz]

Some good points in there, but I cant help but wonder where the funding is going to come from.

[renluop]

"dark fibre" Que?

[asbokid]

dark fibre = not lit - unused - redundant - spare

[renluop]

Next stupid question(s) where's it come from and how did it get there to be unused?
( makes quick exit)

[Black Sheep]

I'm no expert, but I think it is the spare capacity within the fibre itself. In other words, the infrastructure is there but possibly only running at 20% of capability.

[kitz]

Yep..    when the fibre is laid not all of the bandwidth will be in use.   

SDH & Optical Fibre Backhaul

Its usually there for future use..   in fact a certain amount has to be put on one side for the future.   It wasnt too long ago that 2Mbps would have been the norm, but now look at the speeds that can be obtained.    As more homes get VDSL then more of this capacity will be needed, otherwise the interwebs could grind to a halt (congestion).

[waltergmw]

Gentlefolk,

This is my crude understanding.

There are two forms of redundant fibre.

First are physical fibres. You never run just enough for the immediate need.
E.g. BT usually run a sub duct (= an empty pipe) into which is blown a fibre bundle typically of 240 mini-bundles each containing 12 fibres. It can be seen that such capacity could not usually be consumed immediately even if BT  were to do a proper job and run FTTP everywhere in the vicinity.

Secondly far more capacity is available within each fibre if ( more expensive) "modems" are used with greater frequency bandwidth capacity.

Kind regards,
Walter

[kitz]

>> Secondly far more capacity is available within each fibre if ( more expensive) "modems" are used with greater frequency bandwidth capacity.

Unfortunately WDM (Wave Division Multiplexing) is hugely expensive.  Even then WDM can be further split between CWDM and DWDM.. with DWDM kit costing even more*

Because of its high cost its reserved for the backbone and major backhauls.   It certainly wouldnt be ecomonic to use WDM from cab to exchange.   Theres many many exchanges in the UK themselves that cant sustain the cost of utilising  WDM on the backhaul.   

However we are talking technology here and we all know that over time prices do tend to decrease (eg 10 years ago 512k was £30pm) so who is to say what will happen in the future.  But currently WDM is weighed against the cost of laying new cable.

*I believe that although BT do currently use DWDM on their core, they may be looking into using more DWDM  on their major backhaul links, but I'd have to google before I can state anything definite on that.

[waltergmw]

@ Kitz,

Thanks greatly for a much better comment upon my "more expensive" solution.


I had also omitted the lower order local fibre distribution where the big fibre bundles are subdivided in a distribution node (= a fat joint).
At this point the technology changes (slightly) and several small diameter quite different pipes this time usually already containing four tubes fan out to the local FTTCs.
Quite often only one tube in a pipe has a small fibre bundle blown through it at present.
Within the FTTC four individual tiny fibre pipes feed the fibre from a white termination box to the DSLAM plugs.
Clearly this technology will have to change if "Fibre on demand" becomes a common reality.
Perhaps this is the reason for the seemingly extortionate cost of installing the "On demand" FTTP.

{ I have lots of photographs but cannot load them on this site due to the reasonably small (but very necessary) file size limitation}

For an innovative ground-breaking solution designed specifically from day one to provide true FTTP to every house, over vast mainly rural areas, have a look at the splendid efforts up at B4RN.
See several of the later videos and picture sequences e.g.

http://b4rn.org.uk/there-she-blows

Kind regards,
Walter