What is the capacity of twisted pair phone lines?

Guest
Where I live on Whidbey Island the local phone company, Whidbey
Telecom, installed fiber optic conduit to all the customers because
they anticipated the need for fiber optic cable to be able to carry
internet and TV. I asked a phone company technician why the fiber
wasn't installed once the conduit was in and he told me there were
different types of fiber and the phone company didn't yet know which
they were going to use. As it turns out however, we now have phone,
DSL, and TV all over twisted pair copper wires. So the apparently the
technology has advanced to the point that fiber optic cables are not
needed in order to have TV added to the data the twisted pair carries.
So now I'm wondering just how much data can a twisted pair of wires
carry? I'm amazed at how much more information comes down the wires
than what used to be available. I remember a demonstration of a video
phone years ago and not only was the frame rate very low and the
resolution bad but the picture was only black and white. Now my wife
talks to her sister using an iPad and Facetime so they can see video
of each other while at the same time I am talking on the phone or
surfing the web. With the same twisted pair that used to only be
capable of carrying poor black and white video. I realize that digital
is used now instead of analog for the video which makes the good video
possible but just how much information can the old twisted pair wires
carry?
Eric
 
On Fri, 30 May 2014 14:12:03 -0700, etpm wrote:

Where I live on Whidbey Island the local phone company, Whidbey Telecom,
installed fiber optic conduit to all the customers because they
anticipated the need for fiber optic cable to be able to carry internet
and TV. I asked a phone company technician why the fiber wasn't
installed once the conduit was in and he told me there were different
types of fiber and the phone company didn't yet know which they were
going to use. As it turns out however, we now have phone, DSL, and TV
all over twisted pair copper wires. So the apparently the technology has
advanced to the point that fiber optic cables are not needed in order to
have TV added to the data the twisted pair carries.
So now I'm wondering just how much data can a twisted pair of wires
carry? I'm amazed at how much more information comes down the wires than
what used to be available. I remember a demonstration of a video phone
years ago and not only was the frame rate very low and the resolution
bad but the picture was only black and white. Now my wife talks to her
sister using an iPad and Facetime so they can see video of each other
while at the same time I am talking on the phone or surfing the web.
With the same twisted pair that used to only be capable of carrying poor
black and white video. I realize that digital is used now instead of
analog for the video which makes the good video possible but just how
much information can the old twisted pair wires carry?
Eric
Click to expand...

The operative question is "how much information can we figure out how to
get onto the old twisted pair?"

Personally, I don't know the answer. I do know that our local phone
company runs a fiber-optic backbone down the main roads here, with little
boxes that convert to twisted pair for the last mile. Are you sure
that's not what your phone company is doing? It certainly gets more
capacity out of a twisted pair of wires.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Fri, 30 May 2014 16:38:45 -0500, Tim Wescott
<tim@seemywebsite.really> wrote:

On Fri, 30 May 2014 14:12:03 -0700, etpm wrote:

Where I live on Whidbey Island the local phone company, Whidbey Telecom,
installed fiber optic conduit to all the customers because they
anticipated the need for fiber optic cable to be able to carry internet
and TV. I asked a phone company technician why the fiber wasn't
installed once the conduit was in and he told me there were different
types of fiber and the phone company didn't yet know which they were
going to use. As it turns out however, we now have phone, DSL, and TV
all over twisted pair copper wires. So the apparently the technology has
advanced to the point that fiber optic cables are not needed in order to
have TV added to the data the twisted pair carries.
So now I'm wondering just how much data can a twisted pair of wires
carry? I'm amazed at how much more information comes down the wires than
what used to be available. I remember a demonstration of a video phone
years ago and not only was the frame rate very low and the resolution
bad but the picture was only black and white. Now my wife talks to her
sister using an iPad and Facetime so they can see video of each other
while at the same time I am talking on the phone or surfing the web.
With the same twisted pair that used to only be capable of carrying poor
black and white video. I realize that digital is used now instead of
analog for the video which makes the good video possible but just how
much information can the old twisted pair wires carry?
Eric

The operative question is "how much information can we figure out how to
get onto the old twisted pair?"

Personally, I don't know the answer. I do know that our local phone
company runs a fiber-optic backbone down the main roads here, with little
boxes that convert to twisted pair for the last mile. Are you sure
that's not what your phone company is doing? It certainly gets more
capacity out of a twisted pair of wires.
Click to expand...
I'm sure that twisted pair is not being run from the phone company's
main office. There is a box that is about 1.25 miles from me that I am
pretty sure my wires come from. Whidbey Telecom updated all sorts of
boxes here on the south end of Whidbey Island and after all the work
was done on the box closest to me I got an email telling me that TV is
now available over my phone line. So there probably is fiber optic
running from the main office to the boxes. Still, 1.25 miles seems
like a long way for twisted pair when I think back about 15 years and
how to get decent DSL speeds my brother had to switch to cable from
the phone line.
Eric
 
On Fri, 30 May 2014 16:34:27 -0700, <etpm@whidbey.com> wrote:

...snip....
I'm sure that twisted pair is not being run from the phone company's
main office. There is a box that is about 1.25 miles from me that I am
pretty sure my wires come from. Whidbey Telecom updated all sorts of
boxes here on the south end of Whidbey Island and after all the work
was done on the box closest to me I got an email telling me that TV is
now available over my phone line. So there probably is fiber optic
running from the main office to the boxes. Still, 1.25 miles seems
like a long way for twisted pair when I think back about 15 years and
how to get decent DSL speeds my brother had to switch to cable from
the phone line.
Eric
Click to expand...

Think about capacity like spectrum, there's low frequency that pretty much
gets through. At high frequency the 'skin effect' causes major loss. From
memory, DSL instrumentation uses bands spread out along the possible
spectrum as in, "don't put all your eggs in one basket" Thus 'holes' can
get cut out and all pretty much works well. Now, thre is an excellent
reference that gives models for losses versus distance for standard telco
line 24 or 26 Qwg twisted pair that claim to be within 1% up to 10MHz.
That band is 20Mbs. Now if you assign several layers at that speed you get
40Mbs, BUT there is a limit to stacking and noise and all. Look up
Shannon's Theorem, or Limit. Very simple formula derived through
observation.


"ADSL/VDSL Principles"
by Dennis J. Rauschmayer, 1999
Macmillan Technical Publishing
pp 28-42


Back slightly before 2000, this company was making DSL testers and about
the maximum distance could go was 17,000 ft. Today 17k ft yields around
300 kbs, not fast, but better than dial-up.

DSL Test Instrumentation
Sunrise Telecom Incorporated
302 Enzo Drive
San Jose, CA 95138


I live in rural area north of phoenix and used to get calls from our telco
service to get DSL. They promised up to 7MBs!! for only 39.95 per month.
So I asked them WHAT exactly would I get here being 17,261 feet form
switching house. Don't know, but they repeated,"you get up to 7MBs !! for
only 39.95 per month." So, knowing what I know about DSL, I told them I
would pay them proportionately for the speed, would you install it? [Now
between you and me, that comes out to around .3/7 * 39.95 = 1.72] After
telling them to go ahead and install, but I demand them to 'adjust' the
cost to reflect what they actually deliver, they quit calling.
 
<etpm@whidbey.com>
So now I'm wondering just how much data can a twisted pair of wires
carry? I'm amazed at how much more information comes down the wires
than what used to be available. I remember a demonstration of a video
phone years ago and not only was the frame rate very low and the
resolution bad but the picture was only black and white. Now my wife
talks to her sister using an iPad and Facetime so they can see video
of each other while at the same time I am talking on the phone or
surfing the web. With the same twisted pair that used to only be
capable of carrying poor black and white video.
Click to expand...

** The limitations you refer to above were * NOT * due to using twisted
pair cables. Back then, a phone connection only allowed ONE voice
quality signal to be transferred across the network - cos that was what the
system was designed to do.

Some heroic efforts were made to get the most out of the available 3.4kHz
bandwidth to carry data - ending with the 56K modem.

http://en.wikipedia.org/wiki/56_kbit/s_modem

Since then, the former voice only network has changed out of all
recognition to become a massive data transfer network instead, mostly
using optical fibre. Luckily, it still carries voice signals for regular
telephone users - as a courtesy.

The relatively shot run of twisted pair that arrives at your home can
in theory carry massive amounts of data - limited firstly by the maximum
power output of the modem sending it and secondly by the twisted wires
melting or shorting from overvoltage at the sending end.

The huge losses that occur at high ( MHz) frequencies are compensated
for by using high drive levels and sensitive receive end electronics.

If at some distance the data signal starts to disappear into background
noise, then it is only necessary to add in-line boosters to restore it -
as is normally done with undersea cables and optical fibre links.

So the answer to your question is *money* is the final limit. That limit
occurs when it is cheaper to use another technology instead of twisted
copper wires to do the job.



..... Phil
 
On Fri, 30 May 2014 14:12:03 -0700, etpm@whidbey.com wrote:

Where I live on Whidbey Island the local phone company, Whidbey
Telecom, installed fiber optic conduit to all the customers because
they anticipated the need for fiber optic cable to be able to carry
internet and TV. I asked a phone company technician why the fiber
wasn't installed once the conduit was in and he told me there were
different types of fiber and the phone company didn't yet know which
they were going to use. As it turns out however, we now have phone,
DSL, and TV all over twisted pair copper wires. So the apparently the
technology has advanced to the point that fiber optic cables are not
needed in order to have TV added to the data the twisted pair carries.
So now I'm wondering just how much data can a twisted pair of wires
carry? I'm amazed at how much more information comes down the wires
than what used to be available. I remember a demonstration of a video
phone years ago and not only was the frame rate very low and the
resolution bad but the picture was only black and white. Now my wife
talks to her sister using an iPad and Facetime so they can see video
of each other while at the same time I am talking on the phone or
surfing the web. With the same twisted pair that used to only be
capable of carrying poor black and white video. I realize that digital
is used now instead of analog for the video which makes the good video
possible but just how much information can the old twisted pair wires
carry?
Eric
Click to expand...

This is a good question.

I only know from experience that information quantity and distance
are inverse proportional. DSL and other technologies use high
frequency signals, actually it is nothing else than wire-bound radio
transmission. The higher the maximum carrier frequency, the more
information can be modulated on it. DSL uses the complete long,
medium and shortwave radio band from Kilohertz up to 30 MHz.
After a few miles, the HF signals are gone and so is DSL.

w.
 
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