[LINK] Fibre versus copper: ease of repair.

[Crispin Harris]

Hi David,

> On Sun, Sep 12, 2010 at 11:38 AM, David Boxall <
david.boxall at hunterlink.net.au> wrote:
> This assertion has been made on ozpolitic:
> > When a cable with a large number of copper pairs is broken they
> > are simply buzzed out with a multimeter & joined used a telephone
> > link for communication from the other end.
> > It's a lot harder to locate the right optic fiber & join it compared to
copper.
>
> Is there any substantial difference between fibre and copper, in
> relation to identifying the appropriate ends to join in a severed cable?

I spent several hours talking about just this topic with a
central-australian cabling contractor/specialist just the night before last.

His comment was that when there was a "major break" (i.e. all fribres are
broken in a multi-bundle) that the fibre was "way easier to manage, just
fiddly".

His logic went like this:
 - When a backhoe goes through the cable, be it fibre or copper, you get (at
least) 2 breaks.
 - The longer time that it takes to fuse single-mode fibre is easily
compensated for by the ease of identifying which fibre to repair.
 - With fibre, you turn all the lights off, then on both ends, you light the
fibre to be re-joined.
   and then identifying the next pair takes "a roll of the thumb".
 - There is a constant voice-link with techs managing equipment on both ends
of the broken link - this is the same regardless.
 - You need to join/fuse the cable twice or three times - the same in both
cases.
 - with copper, you need to find/keep joiners, with fibre, the fuser "needs
servicing after a couple of hundred joins".

He said he would rather fix a fibre backhaul than copper "any day".

> If so, would said difference add substantially to the cost or time
> involved in repairing a breach in cables of equivalent capacity?

When I pushed him on how long it takes to fuse a fibre in the middle of the
desert, he responded that it took between 5 and 30 minutes depending on "how
the fibre feels" (his quote).

He stated that he has experience completely re-fusing a "back-hoe'd 144-core
armored sub-T cable" (with 3-4 people on the job) in about 24 hours.
He then hurried on to say that this was the total time on-site, and that the
majority of service was recoverred within 45 minutes of unearthing the
breaks (even though this added about 2 hours to the total on-site time
decause of double handling the 5 or 6 active fibres).

Further to this - just how many copper pairs would you need to have to get
the equivalent capacity of 144-core single-mode fibre? (given that these
days, even without DWDM (which ALL the backhaul telco's use) 144 cores is
close to 1.5 TERRabits/second - and DWDM will multiply that by 64, 138 or
256 depending on the vendor/model.)

How much copper cable would be needed to get even 144Gbps? I am thinking
that we are talking in the order of a 500-pair bundle or more - over 1000
wires to join. each one requiring 2 dry-joiners, a patch, 4 crimps and
testing...


Given that this is example comes from just about the most remote and
inhospitable part of the country, I can't see that the numbers would be any
worse when working in less than 45C (and more than 5C over night) and close
to hot coffee/dinner).

Now, he *DID* have disparaging things to say about people with less
experience attempting to do this kind of major work. ("It's not the training
that matters - yes it is important - but fusing fibre is all about the FEEL
of it - my apprentices fuse hundreds of strands on the bench before I let
them do it by themselves in the field. It's about stress, confidence and
calm fingers.")

I hope that this missive adds both knowledge and clarity...

Cheers,
   Crispin

--

> David Boxall                    |  When a distinguished but elderly
>                                |  scientist states that something is
> http://david.boxall.id.au       |  possible, he is almost certainly
>                                |  right. When he states that
>                                |  something is impossible, he is
>                                |  very probably wrong.
>                                                  --Arthur C. Clarke
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-- 
Crispin Harris
crispin.harris at gmail.com
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