[LINK] Fibre versus copper: ease of repair.

Crispin Harris crispin.harris at gmail.com
Sun Sep 12 17:42:59 EST 2010


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
"A great deal of Security is unfortunately just like the underwear of
Brittany Spears.
If it's even there at all, it is needlessly complex and frilly; looks good
without actually covering much; and is far to easy to get around or remove
completely."
 - David Boston

Marriage (n): a natural institution whereby a man and a woman give
themselves to each other for life in an exclusive sexual relationship that
is open to procreation.
 -Definition compliements of Cardinal George Pell, Catholic Archdioces of
Syndey


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