Bobby. wrote on Sep 12
th, 2010 at 12:31pm:
...
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.
I sent your assertion to someone with relevant experience. This is his reply (relevant bits in bold, my specific questions underlined):
Quote:> 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.")
So the answers seem to be:
- it's easy to find the right fibres if you turn out the lights;
- it doesn't take anywhere near as long as the panic-merchants pretend and
- it takes skill and practice, but it's not rocket surgery.
In this respect, it seems fibre is superior to copper. Again.
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