Last Weekend's 'Click'

On 21 Jan, 09:44, "
wrote:
On 20 Jan, 13:20, Java Jive wrote:

Telly tech
Chris Long looks at the new TV technologies showcased at CES:http://www.bbcworldnews.com/Pages/Pr...?id=18&Feature...

"""So now we have Ultra HD, which provides a phenomenal 7,680 pixels
by 4,320. At the moment it is only available on enormous screens, but
it will eventually reach our televisions."""

Not unless we all have 100" TVs, or we all sit 1 foot away from 40"
ones. There's no benefit to having pixels smaller than the eye can
see.

Why not so long as there are enough of them grouped together? After
all, everything that we can see is made up of atoms that we cannot
see!

John

wrote in message
...
Not unless we all have 100" TVs, or we all sit 1 foot away from 40"
ones. There's no benefit to having pixels smaller than the eye can
see.

Why not so long as there are enough of them grouped together? After
all, everything that we can see is made up of atoms that we cannot
see!

Because each pixel would need to be individually addressed, and if a number
of them were driven in concert (a logical thing to do if the individuals
were too small to see) it would be a duplication of data and thus a waste
of bandwidth. And if they are not to be individually addressed then there's
no point in them as individuals, and each group of them might as well be
replaced by one pixel.

Bill

wrote:
On 22 Jan,
"Woody" wrote:

If you are in a Virgin cable area (like me :-}} ) you can now have 50Mb
to your home on fibre.

You've been taken in by the advertising blurb. The fibre will cease a
mile or
more away. The local distribution is by a coax of the ilk of CT100,
usually
with a pair or two of old fashioned tepephone cable.


It is correct to say that you do not have fibre to the home but the rest
of your assumptions are wrong.

The local distribution from the fibre receiver will, typically, be via
amplifiers and trunk cables, the latter with an outer conductor diameter
(under the sheath) of between half an inch and an inch - 0.54" and 0.86"
are commonly used sizes - more than a little bit bigger than CT100! The
majority of cable used will be QR 540 with a loss of 6.07dB/100m.

http://docs.commscope.com/Public/QR 540 JCASS.pdf

http://docs.commscope.com/Public/QR 860 JCASS.pdf

The maximum cascade (number of trunk amplifiers) is usually restricted
to three, possibly with an extra line extender before the local street
to home distribution starts. The cascade limit is primarily determined
by the trade off between noise and distortion in analogue networks - the
main distortion being from the analogue carriers.

From the fibre receiver, the copper network will radiate out in a star
network which means that splitters will eat into the available signal
budget between amplifiers and, therefore, maximum cable lengths.

Considering that the loss of a mile of QR 540 cable alone is 100dB,
Brian's estimate of distance is seriously in error!

Also, by stressing the distance from the fibre receiver, he is implying
that the signal will degrade over the copper network, like ADSL on
telephone lines. There will be some degradation of course - noise and
distortion as mentioned earlier - but these are tightly controlled (and
form part of the conditions attached to the cable operator's licence.)

This is obvious, if you think about it, as such degradations are most
obvious on analogue television pictures, the raison d'être for the cable
network in the first place!

Internet traffic is carried on the cable network in an entirely
different way to ADSL. It uses an MCNS (Multimedia Cable Network System)
channel to carry data conforming to EuroDOCSIS (Data Over Cable Service
Interface Specification). It uses 8MHz channels and, from an RF point of
view, is indistinguishable from a DTV signal. DOCSIS 3.0, which is now
being rolled out to provide the new 50Mbit/s services allows channel
bonding which means that multiple 8MHz channels can be used to extend
available bandwidth.

The final leg of the distribution from the street cabinet to the home is
(usually) on RG6 and is unlikely to exceed much over 150m (although RG11
can be used if the run has to be longer.) The signal leave the tap with
a forward slope (ie: rising with frequency) and, depending on distance,
will arrive at the subscribers modem with a slope that varies from
forward, through flat, to inverse. However, the slope across an
individual 8MHz channel will be so slight that it will be virtually, if
not impossible, to measure.

In practice, the quality of the internet service provided to the
subsrciber at the very limit of the copper network will be identical to
the subscriber who has the fibre receiver in the street in front of his
house!

As for any "old fashioned tepephone cable" (sic) which accompanies the
RF drop cable, this will be used ONLY for the provision of an "old
fashioned" telephone service and nothing else!

Terry

"Terry Casey" wrote in message
...
wrote:
The local distribution from the fibre receiver will . . .

A very interesting post.

Bill

"Terry Casey" wrote in message
...
wrote:
On 22 Jan,
"Woody" wrote:

If you are in a Virgin cable area (like me :-}} ) you can now have
50Mb
to your home on fibre.

You've been taken in by the advertising blurb. The fibre will cease
a
mile or
more away. The local distribution is by a coax of the ilk of CT100,
usually
with a pair or two of old fashioned tepephone cable.




Actually that is exactly what VM already do - at least around here - but
the last run is only a hundred metres or so.

Having said that I would suspect that the effects of the cable might
still stop 50Mb being viable even over such a short distance.

Having read other places (in the trade) the intended move is towards
fibre into the home, and that is certainly what is being done in other
parts of Europe and is already in place in the Far East.


--
Woody

harrogate three at ntlworld dot com

Bill Wright wrote:
"Terry Casey" wrote in message
...
wrote:
The local distribution from the fibre receiver will . . .

A very interesting post.

Bill


Thank you, kind sir!

Incidentally, a typical fibre receiver will feed up to 2,400 homes -
hence the star configuration.

There was a move to 600 home nodes (smaller than one of your's that you
mentioned recently, IIRC!) but, on the networks I worked on, they were
lumped into 2,400 home groups for DTV rollout. These can, of course, be
un-grouped if demand increases - I'm thinking internet here - which will
give such areas a head start if demand keeps increasing.

On the other hand, by getting rid of the analogue channels (as has
already happened in a couple of places) the channel bonding offered by
DOCSIS 3.0 will permit up to 16 individual 8MHz channels to be treated
like one contiguous 128MHz block of bandwidth! Not surprising that VM
are considering 200Mbit/s services in the future!

As the Commscope cable spec links got trunkated by the spaces in the OP,
here they are again in a format which should keep them intact.

http://docs.commscope.com/Public/QR%20860%20JCASS.pdf

http://docs.commscope.com/Public/QR%20540%20JCASS.pdf

Terry

Woody wrote:
"Terry Casey" wrote in message
...
wrote:
On 22 Jan,
"Woody" wrote:

If you are in a Virgin cable area (like me :-}} ) you can now have
50Mb
to your home on fibre.
You've been taken in by the advertising blurb. The fibre will cease
a
mile or
more away. The local distribution is by a coax of the ilk of CT100,
usually
with a pair or two of old fashioned tepephone cable.



Actually that is exactly what VM already do - at least around here - but
the last run is only a hundred metres or so.

Having said that I would suspect that the effects of the cable might
still stop 50Mb being viable even over such a short distance.


I am a bit puzzled here because your post starts by quoting MY post on
the subject which you have then chosen to totally disregard and delete
all trace of!

If you cannot understand what I wrote, I apologise. Obviously you
require a much simpler explanation!

Hopefully, this will start you thinking on the right lines ...

First of all, disregard the red herring that Brian introduced - VM do
not use telephone pairs for broadband. The broadband service is provided
over coaxial cable and does not degrade over distance like ADSL on
telephone lines.

The useful bandwidth of the coax is determined by loss, distance and
frequency. The upper frequency used by the VM network is 750MHz and the
design ensures that 750MHz signals reach the subscriber at sufficient
level to provide a good service. Obviously, as losses reduce with
frequency, all lower frequency signals MUST be of suitable quality.

VM send TV & data signals along this cable at frequencies ranging from
126 - 750MHz - a bandwidth of 624MHz. In practice there are gaps in this
range which are not used but the reasons don't concern us here so let's
take 600MHz as a convenient round figure.

Now forget all about modern high compression transmission schemes and
assume we've only got a simple system which carries data at just one bit
per cycle of bandwidth - 1bit/Hz

So now our rather crude system is capable of delivering 600Mbits/s to
every subscriber on the network - no matter where they are.

In practice, of course, this bandwidth is split up into 8MHz chunks - or
channels - which are used to carry individual analogue TV channels,
'bundles' of digital TV channels and data 'bundles' for the internet.

As I said in the post you ignored, the last two are indistinguishable
from an RF point of view, so it is equally suited to carrying THE SAME
DTV pictures and internet traffic to everybody.

The suggestion that you responded too and agreed with is like Bill
telling his customers that they can only get BBC1 on their TV because
the cable feeding them is so long that all the others got lost on the
way .......!

Terry

wrote:
On 23 Jan,
Terry Casey wrote:

First of all, disregard the red herring that Brian introduced - VM do
not use telephone pairs for broadband. The broadband service is provided
over coaxial cable and does not degrade over distance like ADSL on
telephone lines.

I may have not explicitly stated, but I gave a very strong inference that the
pairs were for POTS, and the BB was on the coax.


I think that the impression you gave to most people reading your post,
who are more likely to be familiar with ADSL distribution, that not
being directly fed by fibre would lead to degradation of speed with
distance from the fibre node.

This is not true and my intention was only to correct that impression.
If you and others have also been educated in the process, I am pleased
to have been of service.

As I said in my earlier post, "the quality of the internet service
provided to the subscriber at the very limit of the copper network will
be identical to the subscriber who has the fibre receiver in the street
in front of his house!"


VM do use (BT) telephone pairs for BB, but not in their cabled areas. There
are, however, islands of new development within our local area where the only
VM BB available is via this route. It appears that they do not extend their
cable into new developments.


Originally, you were referring to premises fed by VM's cabled network.
VM do not provide 'off-net' services to its own customer base!

By referring to VM's 'off-net' service via BT pairs to customers who
could not otherwise be served, you are again attempting to muddy the
waters. The discussion was specifically about cable supplied services -
if you wish to query VM on their build policy, especially WRT to new
developments, please feel free to contact them and ask!

Terry

wrote:
On 21 Jan, 04:46, Java Jive wrote:
Until there's flames, or a seascape, or a flock of birds taking off,
or a shoal of fish, or a waterfall, or river rapids, or any one of
many situations where the bandwidth can't maintain the bitrate, then
analogue, assuming it hasn't itself gone through any digital stages
involving compression before being broadcast as analogue, is better.


Perhaps, but only for that one channel. The problem is that analogue
is greedy and requires an entire UHF number solely for one broadcast,
whereas with DTT, it is possible to fit in multiple broadcasts in the
same bandwidth.

I know where you're coming from, but you could in theory actually have the
best of both worlds. DVB-T2 gives a payload of about 36 Mb/s, that is
accommodated in an 8 MHz wide UHF or VHF allocation.

It would never be allowed to happen, but that could carry an SD channel at 34
Mb/s, and I would defy Mr J.Jive to notice any motion artefacts on his
domestic receiving equipment. Very few would notice problems if you had three
SD transmissions running at 10-12 Mb/s.

Composite analogue transmission has some really annoying artefacts of its own.
Chroma/luma cross colour and patterning. Unavoidable ghosting for many folk,
patterning and interference from an increasing amount of RF pollution.

On balance, I prefer a decently encoded and bit rate allocated MPEG broadcast,
to analogue. YMMV.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

In article , Terry Casey wrote:
As I said in my earlier post, "the quality of the internet service
provided to the subscriber at the very limit of the copper network will
be identical to the subscriber who has the fibre receiver in the street
in front of his house!"

As we should expect. The copper part of a cable broadband and broadcasting
service has been *designed* for its purpose, unlike the case with ADSL
which is a bodge applied to a system invented in the days of Queen
Victoria for a quite different purpose.

Rod.
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