Advice, please

On Fri, 23 Apr 2010 18:58:14 +0100, Roderick Stewart
wrote:

In article , Graham. wrote:
Fibre is very new technology for our industry. On the face of it there
are many advantages, and I have no doubt that in a few years it will
be the standard technolgy for larger systems.

I was wondering that myself! As technologies converge further and the
poor old cable has to carry higher and higher data volumes, I wonder
if fibre optics are better placed to do that?

Better for higher data volumes certainly, but I don't know the maximum run
length that can be used without repeaters. Perhaps somebody who knows can
enlighten us? I suspect it's nowhere near what can be achieved (albeit at
lower data rates) with ADSL, and thus will be dependent on electronics in
street-boxes, with all the reliability implications of that.

If you've got reasonably good ADSL, hang onto it because there's nothing
between you and the exchange but wire, so a great deal less to go wrong
than with any system that requires powered electronics in the street.

Rod.


The sky is the limit - it depends on the launch power and the make-up
of the fibre. A launch level of 30dB will get you to around 300km,
possibly further at a lower launch level but would then need Raman
amplification.

The above is a little pricey, so a 1300nm laser will probably
comfortably achieve over 300 metres
--
Cheers

Peter

(Reply to address is a spam trap - pse reply to the group)

"Roderick Stewart" wrote in
message

Better for higher data volumes certainly, but I don't know the maximum run
length that can be used without repeaters. Perhaps somebody who knows can
enlighten us?

Several - many - kilometres. The loss is astonishingly low - typically
0.3dB/km or less. It varies with wavelength, of course. I was amazed when
I found out that - if the Atlantic Ocean were made of the same stuff - you
could see all the way to the bottom with ease.

The data capacity is astonishingly high - almost infinite, really - and is
primarily limited by the electronics at each end, and in the repeaters.

Also, you can send light in both directions at once without interference.

Fibre-to-the-home (FTTH) has a massively longer reach, and massively higher
bandwidth potential, than any variant of DSL technology (of which, even the
inventors labelled it "an interim technology").

It is highly unlikely that any street electronics would be required for
FTTH. On the other hand, it is incredibly expensive to provide a strand of
fibre to all 20+ million addresses BT servers. I think BT has around
100,000 cabinets (primary cross connection points, or PCCPs), so providing
fibre to them is going to be very much cheaper. Then, of course, it will
require street electronics in each cab, to convert back to copper with POTS
(plain old telephone service) plus DSL.

There are issues around fibre to the home - a big one being that you can't
carry electricity along it. So that implies local power for the electronics
at the customer premises. Plenty of hassle finding room for it, keeping it
powered, swapping out knackered standby batteries, etc. Not really a
problem if the fibre only goes to the cab.

There are other problems - for example, it's very early days for providing
fibre using overhead cables. Currently they install a plastic tube and then
blow the fibre along it. But issues such as trees rubbing through the tube
must be allowed for.

FTTH is quite likely to involve what's known as a PON (passive optical
network). One fibre from the exchange is split into two or four, and then
split again, such that it can feed up to 32 end points. The splits are
provided wherever the locality requires. Again, this is a great deal
cheaper than running all 32 end points back to the exchange in their own
fibres.

The PON works on a time division multiplexing system, which of course limits
the bandwidth each end point can "see".

When I left BT, the view was that individual fibres may be provided to high
revenue sites such as large businesses, and PONs used for domestic
distribution.

If you've got reasonably good ADSL, hang onto it because there's nothing
between you and the exchange but wire, so a great deal less to go wrong
than with any system that requires powered electronics in the street.

Well, I wonder if you'll get a choice. Still, it's true that ADSL requires
just a copper pair back to the exchange. When I did some reliability
modelling on candidate fibre access network architectures, the MTBF wasn't
that dissimilar, although the cost of each failure was much higher. Also,
of course, there are single-point-of-failure issues with the street
electronics, which is simply to say that one failure of the street
electronics may knock out a few hundred customers at once, which is rarely
the case with copper (except for dig-ups).

It's going to be interesting, although I'm having trouble visualising a
useful role for a 100Mb/s (or whatever) internet connection. I currently
have a 16Mb/s connection, and the bottlenecks are almost always elsewhere in
the Internet. The Internet itself may need some substantial uplift before
the potential of FTTH or FTTC can be exploited.

SteveT

On Fri, 23 Apr 2010 06:58:27 -0700 (PDT), John wrote:

If I aim for breakeven, I shall certainly make a loss!

You are right, and my accountancy background has given me enough skill
to be able to administer the finances of it, but the thought of having
to do tax returns fills me with woe. 8-((

Ah, you have finally convinced me you really are completely barking mad.
They've obviously just let you out again seeing as you haven't been
around here for a while.
Strangely Jerry the village idiot (or pillock as he now likes to call
himself) has reappeared as well.

MESSAGE BEGINS

In message , Petert
writes
On Fri, 23 Apr 2010 18:58:14 +0100, Roderick Stewart
wrote:

In article , Graham. wrote:
Fibre is very new technology for our industry. On the face of it there
are many advantages, and I have no doubt that in a few years it will
be the standard technolgy for larger systems.

I was wondering that myself! As technologies converge further and the
poor old cable has to carry higher and higher data volumes, I wonder
if fibre optics are better placed to do that?

Better for higher data volumes certainly, but I don't know the maximum run
length that can be used without repeaters. Perhaps somebody who knows can
enlighten us? I suspect it's nowhere near what can be achieved (albeit at
lower data rates) with ADSL, and thus will be dependent on electronics in
street-boxes, with all the reliability implications of that.

If you've got reasonably good ADSL, hang onto it because there's nothing
between you and the exchange but wire, so a great deal less to go wrong
than with any system that requires powered electronics in the street.

Rod.


The sky is the limit - it depends on the launch power and the make-up
of the fibre. A launch level of 30dB will get you to around 300km,
possibly further at a lower launch level but would then need Raman
amplification.

That is Goldfinger stuff! Are you ignoring all the problems of fibre
non-linearity and power-related distortions and other nasties? There's
only so much you can do in the way of pre-correction. As low as around 7
to 10dBm, things like Brillouin scattering start to happen.

Most ultra linear CATV transmitters (carrying an AM spectrum of 50 to
1000MHz) don't launch directly into fibre at much more than about 13dBm,
giving a maximum reach of around 35km (to an optical receiver requiring
0dBm input), and typically around 20 to 25km to an optical amplifier.
With data carried by digital (pulsed) modulation, the receiver can work
to a much lower level (as low as -26dBm or even less), so the range is
correspondingly longer.

The above is a little pricey, so a 1300nm laser will probably
comfortably achieve over 300 metres

With a fibre loss of typically 0.36dB/km at 1310nm, I would hope to get
a lot more than that from an optical transmitter. Did you mean 300km?
--
Ian

In article
..com, John scribeth thus


Firstly, the LNBs fitted to the dishes will not be the conventional
ones, but will turn the satellite signal into light, which will be fed
down fibre optic cables. *

Why, are the distances -that- great?

Yes. It is a twenty-one story building, with long corridors.

Also, I was told that this method would not be subject to
interference, nor would it interfere with the existing communal TV
system, even though the cables would run next to each other down the
dry risers.


Seems to me it will be quite an installation job overall so someone who
knows what there doing will be called for.

The idea of fibre though seems rather overkill, after all as others have
said the distances aren't that great..

Be interesting to know how much they want for the job expect it will be
well into 4 figures..

Do your other residents really need all those sat signals or wouldn't
they just be content with Sky at 28.2?...

--
Tony Sayer

On Fri, 23 Apr 2010 20:50:19 +0100, Ian Jackson
wrote:



The sky is the limit - it depends on the launch power and the make-up
of the fibre. A launch level of 30dB will get you to around 300km,
possibly further at a lower launch level but would then need Raman
amplification.

That is Goldfinger stuff! Are you ignoring all the problems of fibre
non-linearity and power-related distortions and other nasties? There's
only so much you can do in the way of pre-correction. As low as around 7
to 10dBm, things like Brillouin scattering start to happen.

No, I maintain a system that does just that - launch is at 30dB
(1500nm) or 1 watt if you prefer.

Most ultra linear CATV transmitters (carrying an AM spectrum of 50 to
1000MHz) don't launch directly into fibre at much more than about 13dBm,
giving a maximum reach of around 35km (to an optical receiver requiring
0dBm input), and typically around 20 to 25km to an optical amplifier.
With data carried by digital (pulsed) modulation, the receiver can work
to a much lower level (as low as -26dBm or even less), so the range is
correspondingly longer.

The above is a little pricey, so a 1300nm laser will probably
comfortably achieve over 300 metres

With a fibre loss of typically 0.36dB/km at 1310nm, I would hope to get
a lot more than that from an optical transmitter. Did you mean 300km?

No, I was referring to what Greenwoods say a fibre patchcord would
achieve at 1310. For a domestic installation I guess that would be
more than adequate. I normally assume a loss of 0.2dB/km.
--
Cheers

Peter

(Reply to address is a spam trap - pse reply to the group)

On Fri, 23 Apr 2010 20:04:30 +0100, "Steve Thackery"
wrote:


"Roderick Stewart" wrote in
message

Better for higher data volumes certainly, but I don't know the maximum run
length that can be used without repeaters. Perhaps somebody who knows can
enlighten us?


There are other problems - for example, it's very early days for providing
fibre using overhead cables. Currently they install a plastic tube and then
blow the fibre along it. But issues such as trees rubbing through the tube
must be allowed for.

It's not really! - BT did provide a partially overhead route for an
admittedly trunk route in West Wales in the 1980's, but I agree with
you that overhead fibre to the home is a long way off.

--
Cheers

Peter

(Reply to address is a spam trap - pse reply to the group)

"Petert" wrote in message
...

It's not really! - BT did provide a partially overhead route for an
admittedly trunk route in West Wales in the 1980's, but I agree with
you that overhead fibre to the home is a long way off.

Tree damage is, and has been, a perennial problem for any kind of overhead
cable route, whether fibre or cable. Ditto damage from high vehicles.

Anyway, I only mention it out of interest - of course BT has a lot of
experience with overhead routes, but many people on this newsgroup might not
be aware of such things.

SteveT

In article , Petert wrote:
With a fibre loss of typically 0.36dB/km at 1310nm, I would hope to get
a lot more than that from an optical transmitter. Did you mean 300km?

No, I was referring to what Greenwoods say a fibre patchcord would
achieve at 1310. For a domestic installation I guess that would be
more than adequate. I normally assume a loss of 0.2dB/km.

Sold. I can see there might be practical problems providing direct runs
with only passive joints from exchanges to homes, but if we can overcome
them there is a huge advantage to be gained by keeping electronics out of
the street.

Roll on the future, but the governmental nincompoops that think we all
need superfast broadband need to realise that our interests will be far
better served by providing *super-reliable* broadband, even if it's not so
fast.

Rod.
--
Virtual Access V6.3 free usenet/email software from
http://sourceforge.net/projects/virtual-access/

"Roderick Stewart" wrote in
message .myzen.co.uk...

Sold. I can see there might be practical problems providing direct runs
with only passive joints from exchanges to homes, but if we can overcome
them there is a huge advantage to be gained by keeping electronics out of
the street.

See my post of yesterday. There is no problem running fibre from exchanges
to homes with only passive joints. PONs (see previous post) were first
trialled by BT back in the mid-'90s.

The issue isn't loss, it's the cost of providing a fibre tail to every
domestic end-point. Hence the compromise of providing fibre to the cabinet,
and pushing DSL over the remaining (and hence considerably shorter) copper
tails.

SteveT