BT and leased lines.

Hi guys.

Do you know if BT's using singlemode fibers or multimode?
I thought they are using singlemode, but I saw a MM fiber connected to my
equipment.
Then in goes via cupler to some white fiber, but it doesn't say whether or
not it's singlemode...

Just wondering.
Anyone knows?

Martin

 

What's "fiber" and "cupler" ?

 

Easily overlooked typos except to grammar and spelling nazis...

 

A firm of solicitors ;o)

 

Generally BT uses monomode to deliver corporate services
(5/125 is common, nowdays it may be blown fibre)
and they charge an arm and a leg for
their NTU with battery backup - UNLESS - they are quoting
against C&W or Telewest. With blown they can add extra fibres
and services and repairs are easier that trying to splice
in a manhole with water lapping over your wellies.
Their presentation to the user may be multimode or monomode,
depending on what the customer requests and can accomodate.
BT's customers premises NTU usually provides BT with
monitoring capability so that if you report a fault their
network control center can check the circuit out from
their end, and create a loopback for end to end testing
if necessary.
It is not unusual for the customers fibre transceiver to
go marginal, the source diodes are run fairly hard.
There is generally some terminating equipment, like
a rack card, or box, between BT's fibre and the users
connection.

 

What's "fiber" and "cupler" ?

Sorry master. Coupler and "fibre". It's not my fault I'm not British and not
my fault that english we learnt at school was something between British and
American.

m.

 

[..]

I was wondering, because somebody cut our fibre outside, and as I've noticed
it was a singlemode fibre (or monomode -- however you call it). But in the
building we've got multimode fibre.
I've spoken to BT guy and he told me they're using singlemode and he said it
only goes to the patch panel at exchange and it doesn't go to any equipment.
It's just a purely dedicated line.
So what if I connect my 1000Base-ZX GBIC module, which can do 100kms? Would
it work?
I haven't tried in the UK yet, but I tried in few other countries and it did
work.

Martin

 

Don't worry, only Jimmy doesn't understand you.

 

Without knowing what's BT's presentation at your end it's hard to be
specific. It would be unusual for BT to splice monomode onto multimode.
It might work ok from them to you (with losses going from monomode to
single mode) but you would need to launch sufficient optical power to
overcome the losses going from multimode to monomode, which is
why it might just work, but is not a preferred solution. A lot depends
on range. At the exchange the monomode terminates on a patch panel,
what he didn't say was what the other side of the panel feeds, most
likely a card, speculatively it could be one of a set of cards that link
to a multiplexed higher rate circuit.
BT can bring in monomode and offer you a dedicated circuit to anywhere
in the world, like your back office in Hong Kong, at a price.
Or you can split a circuit between voice and data, n by 64k channels
for the PABX and the rest of the bandwidth for Ethernet.

There has to be a from/to, how far and does the from/to cross one
or more exchange boundries? They could just give you dark fibre,
like the old wires only circuits that you could lease from BT, but
it would be unusual.

 

but you would need to launch sufficient optical power to

He came with a funny laser pointer (1mW) and the guy on the other end could
see the light. Distance in straight line is about 8 miles.
But I'm not quite sure whether or not they tried to see the light on the
exchange or the other end.
Anyway, I've got 1000Base-ZX converters, which can do 100km on a singlemode
fibre.

It's about 8 miles in straight line; at least two exchanges, but as I'm
calculating it will be about 5.

Can I ask you a stupid question? What is a "dark fibre"?


Thanks,
Martin

 

Dark fibre is the term for unused fibre, just the fibre, with
or without any connectors. Like if you put in an 8 or 12
core fibre, but currently need only a pair, the remaining fibres
are called dark fibre. Some international routes have
dark fibre to allow for future expansion of capacity.

An ordinary torch works quite well if the far end can be
shielded from direct light. I use it to identify which of a
pair is which, assuming spliced on tails with ST
connectors, and you can't determine it from the cable
itself, often the case with blown fibre. You end
up with 8 or 16 connectors and have to determine
which goes to which on a panel, so you get your
mate on his mobile, and he has a torch.

Multi-pair fibre circuits are quite common, a pair each
for Personnel, Sales, Shop Floor or whatever, and you
need to isolate them from each other with a router, like
you don't want Sales to be able to access the Payroll
and see who is being paid what. So that's 3 pairs,
and a dark pair, if it's an 8 fibre cable. Hospitals are
the same they have dozens of independent
departments.

 

Dark fibre is the term for unused fibre, just the fibre, with

Thanks for the answer. I will give it a try probably next month when I go to
data centre.
Think is worth a try. We've got few leased lines on two fibres, so I can
connect GBIC modules (RX and TX). New lines work on 1 fibre :-(

m.