DComTalk.com

James Knott <james.knott@rogers.com> wrote:

Floyd L. Davidson wrote:

The 25 pair cable used for inside plant is not CAT3 (and does
not meet CAT3 specs in several respects).  50 pair cable is
fairly rare, and is not "also often used".  The 25 pair cables
used to wire channel banks are of course only used for the analog
Voice Frequency side.  ABAM is used on the digital side.

Anyone who uses 25 pair telephone cable for 10baseT data, or
even for T1/DS1 data, should be on the layoff list.  T1/DS1, if
it spans more than 5 racks in the same row or to a different
row, is supposed to be individually shielded pairs (ABAM).  Can
you imagine the effect of wiring an office with CAT3 instead?
(There is a fundamental difference between a CO and a customer
location, and the sheer volume of circuits is what makes it
significant.  A few runs of CAT3 is one thing, and thousands of
them is entirely different.)

Take a look at http://www.national-tech.com/catalog/te ... cables.htm and
tell me that again.

Again you are confusing the difference between useful spectrum
and potential spectrum. I did *not* say that you cannot buy 25
pair CAT3 cable. Indeed *you* probably do! But typically it is
more expensive than other cable that is equally suitable...

BTW, what you see in catalog advertisements has very little
meaning. I saw a web page a few days ago that was labeling flat
satin cable as CAT3, in a rather devious way which I took to
mean that it was not done by accident.

As for the date. I don't have hard evidence for when cat 3 was created or
evolved, but this little narrative describes it's application (and cat 4)
in plans made in 1990. So it was already in use for them to have been able
to specify it.

The dates that I found said 1991, which would be when the spec
was ratified, not when it would be commonly discussed or even
available for sale.

That hardly changes the point though. You are creating a great
to-do about nothing of significance.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com

In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:

That just isn't true. The receiver is a voltage sensitive
device. End of story.

??? ethernet transceivers are coupling transformers.
They fundamentally respond to current, not voltage (although
they have a characteristic impedence and it takes voltage to
produce current).

Arcing? From a ringer? I've never heard of such.

DC ringer. AC ringers don't need contacts.

Trust me, splitting voice is *precisely* the same as
splitting data: a total disaster.

I very much doubt it, especialy if there are no other
phone/LF services nearby. Silver satin and various forms
of untwisted cable are perfectly fine for voice. I do not
see much difference between untwisted cable and split pairs
unless the split conductors are themselves paired.

-- Robert

Robert Redelmeier <redelm@ev1.net.invalid> wrote:

In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
That just isn't true. The receiver is a voltage sensitive
device. End of story.

??? ethernet transceivers are coupling transformers.
They fundamentally respond to current, not voltage (although
they have a characteristic impedence and it takes voltage to
produce current).

Or does it take current to produce voltage? Or are you chasing
your tail?

The fact is the *receiver* is a voltage sensing device.

Arcing? From a ringer? I've never heard of such.

DC ringer. AC ringers don't need contacts.

And just how many telsets use a DC "ringer"? And why is ring
current AC? ("I've never heard of such".)

Trust me, splitting voice is *precisely* the same as
splitting data: a total disaster.

I very much doubt it, especialy if there are no other

Well, I can lead you to the water, but...

Like I said, the result is *precisely* the same.

phone/LF services nearby. Silver satin and various forms
of untwisted cable are perfectly fine for voice.

That is simply *not* true. The amount of unbalance is less at
lower frequencies, and to the degree that VF circuits use fewer
high frequency components they are affected less. Some data
formats of course us fewer low frequency components, so they are
necessarily affected more. But at any given frequency the
imbalance and resulting impairments are *precisely* the same.

While a handful of silver satin patch cords that are 6 feet long
will work fine at voice frequencies, attempting to use longer or
more cords is an invitation to trouble.

The same is true of data circuits. I've seen people wire DSX-1
and T1 circuits with silver satin, in a telephone office no
less! It worked. And because it worked we didn't ask for an
outage to correct it either.

Incidentally, in another group someone mentioned replacing
~70M of flat satin with twisted pair to correct problems with
an ADSL circuit. In the discussion that followed, one fellow
laid out 150 feet of RG6 coax, and patched his ADSL through it!
It worked. He said the phone had a barely audible buzz.

Interesting examples, because the 70m of flat satin could be
about half expected to work, and I doubt that anyone would
expect 50m of coax to work. But the one didn't and the other
did, /in/ /those/ /particular/ /situations/.

I do not
see much difference between untwisted cable and split pairs
unless the split conductors are themselves paired.

Well barbed wire works fine too, as long as there are no
external fields to induce interference.

Unbalance on a cable may or may not result in a circuit
malfunction, but to the degree that there is unbalance there is
potential for interference. The degree of imbalance from a
split pair is relatively greater for any given length of cable
than is the imbalance from non-twisted cable pairs.

Which is to say that if you use a 6' flat satin cord with a
split pair in it, there is almost *no* chance that the imbalance
will be enough to present a problem. It can be measured though,
if you have some very good test equipment.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com

Robert Redelmeier wrote:

Arcing?  From a ringer?  I've never heard of such.

DC ringer.  AC ringers don't need contacts.

I've never seen a DC ringer used on a telephone, though I have seen them
with intercoms, that use telephone sets. In that situation though, the
buzzer was on a separate pair.

Floyd L. Davidson wrote:

Well barbed wire works fine too, as long as there are no
external fields to induce interference.

Unbalance on a cable may or may not result in a circuit
malfunction, but to the degree that there is unbalance there is
potential for interference.  The degree of imbalance from a
split pair is relatively greater for any given length of cable
than is the imbalance from non-twisted cable pairs.

At one time, telephone lines were simply one wire & ground. Lots of noise.

floyd@barrow.com (Floyd L. Davidson) writes:

Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:
floyd@barrow.com (Floyd L. Davidson) writes:

Of course. But "telephone lines" are CAT1 grade cable, by
definition. And most certainly 10baseT was *not* designed to
use telephone cable. It was designed specifically to use the
new CAT3 *data network* cable.

And I run 10baseT on a piece of that 3-pair 1980 cable in my house.
I even got away with U-channel on the third pair..

{Kids, don't try this at home without adult supervision}

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

{"Ringing can not interfere with 10BaseT; it's the wrong freq.."}

Here's another way to think about it. Move from the frequency domain
to the time domain. At point t1, the 20Hz signal is zero. But at point
t2-t6 it's big vice that Ethernet on the adjacent pair....and that's
what may KO the bits going by...


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

floyd@barrow.com (Floyd L. Davidson) writes:

A colleague of mine told me about one of his customers who had plugged in an
RJ11 phone line into a 10BaseT NIC RJ45 connector. Everything worked fine
until the phone range and the ringing voltage took out the NIC, motherboard
and power supply....

Wow.

And for real phun, do this in a lightning-prone area.... SURE, that
telco protector is going to save your ass every time......RIGHT?

I have always ranted about external modems [POTS or ISDN..] and having
a hub/switch in front of the motherboard's Ethernet port, etc.

In the real world, specs like the 1500v NIC one are good starting
places, but....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Robert Redelmeier <redelm@ev1.net.invalid> writes:

Arcing? From a ringer? I've never heard of such.

DC ringer. AC ringers don't need contacts.

DC ringers? Where?
1A2 Keysystems had buzzers....
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

Rich Seifert <usenet@richseifert.com.invalid> writes:

10BASE-T contains a minimum electrical *isolation* requirement of 1500 V
rms, per IEC 60950. However, this only means that the isolation
transformers (present on all 10BASE-T signal lines) must not break down
under this stress. It does NOT mean that 10BASE-T devices must survive
1500 V presented differentially across a given pair.

And others have talked about a case where ringing did one in....
Guess that NIC's engineering team didn't read enough or....

-It must be able to reject sinusoidal signals with frequencies under
2 MHz and amplitude up to 6.2 V peak-to-peak. (IEEE 802.3 section
14.3.1.3.2(b).)

Thanks for adding some data to this thread....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

floyd@barrow.com (Floyd L. Davidson) writes:

-Battery voltage is generally 56 Vdc applied through 400 ohms.

"Generally" it would be 52-54 VDC, and "generally" would not
exceed 56 VDC (a 48 volt plant on boost charge). However, I've
seen subscriber line carrier systems that used 75 volts! And of
course that odd circumstance has to be designed for.

How about loop extenders, such as Lorain made? Didn't some raise
the loop voltage to get more talk level on Farmer Brown's line?

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

David Lesher <wb8foz@panix.com> writes:

Here's another way to think about it. Move from the frequency domain
to the time domain. At point t1, the 20Hz signal is zero. But at point
t2-t6 it's big vice that Ethernet on the adjacent pair....and that's
what may KO the bits going by...

Oh, its even worse than that. The ringers I recall from the days of
mechanical bells all had inductors that had a little flapper (just
like on a relay) that normally had an air-gap. When the flapper was
pulled over that gap closed. That changed the inductance greatly.
The resulting dL/dt puts a nice spike into the otherwise smooth 20hz
sine wave.

The full equation for the voltage across the inductor is really

e = L di/dt + i dL/dt

We are so used to working with fixed-inductance inductors that it is
easy to forget about the (i * dL/dt) term.

To see this dL/dt effect in action one can drive a relay with a
low-frequency sine wave (say 1hz - 10hz) and put a scope probe across
the relay. At the point the relay pulls in one should see a little
spike. It might help to increase the signal generator's impedance a
bit by adding a series resistor.

-wolfgang

David Lesher <wb8foz@panix.com> wrote:

James Knott <james.knott@rogers.com> writes:

Robert Redelmeier wrote:

AFAIK, ringing voltage is 90V max P-P

Actually, it's 90V RMS, or about 255V P-P.

On top of -48 DC of course...

And of course except for when it is 105 VAC, on top of -56 VDC.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com

In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:

phone/LF services nearby. Silver satin and various forms
of untwisted cable are perfectly fine for voice.

That is simply *not* true. The amount of unbalance is less at
lower frequencies, and to the degree that VF circuits use fewer
high frequency components they are affected less. Some data
formats of course us fewer low frequency components, so they are
necessarily affected more. But at any given frequency the
imbalance and resulting impairments are *precisely* the same.

Now who is being pedantic? Voice is nowhere near data
in frequency. So the truism of idential impairments has
no practical effect.

While a handful of silver satin patch cords that are 6
feet long will work fine at voice frequencies, attempting
to use longer or more cords is an invitation to trouble.

??? most of telco outside wire is Cat0, essentially identical to
silver satin but solid with weather/burial protection. A lot of older
wire is even worse, with even paper insulation. Yet hundreds of
millions of circuits all work fine over thousands of feet per run.

Incidentally, in another group someone mentioned replacing
~70M of flat satin with twisted pair to correct problems
with an ADSL circuit.

Of course twisted pair is better. Expecially an EMI noisy
environment. But the difference is marginal. With digital,
marginal effects can make large differences.

Well barbed wire works fine too, as long as there are no
external fields to induce interference.

Precisely. Which is why local field strength is an issue.
A split pair causes no trouble if there's nothing to
interfere with it (troublesome freq). One split voice pair
in a shared sheath isn't much problem, although it will pick
up more 60 Hz hum. Two are definitely a problem, especially
since they're likely to be split on each other. Either way,
the data won't care so long as it's not split.

Unbalance on a cable may or may not result in a circuit
malfunction, but to the degree that there is unbalance there
is potential for interference. The degree of imbalance from
a split pair is relatively greater for any given length of
cable than is the imbalance from non-twisted cable pairs.

Granted, but I see that difference small (~20%) comparing with
with twisted pair. And under some circumstances, non-twisted
pairs would be _worse_ than split pairs (think side-by-side flat
pairs vs USOC)

Which is to say that if you use a 6' flat satin cord with
a split pair in it, there is almost *no* chance that the
imbalance will be enough to present a problem. It can be
measured though, if you have some very good test equipment.

More than that. I've pushed 10baseT fine through 50ft silver
satin with USOC pairing. It totally fails as side-by-side.
I suspect 10baseT could be pushed through a good length of
quad with diagonal pairing so long as it wasn't too kinked.

-- Robert

David Lesher <wb8foz@panix.com> wrote:

floyd@barrow.com (Floyd L. Davidson) writes:

-Battery voltage is generally 56 Vdc applied through 400 ohms.

"Generally" it would be 52-54 VDC, and "generally" would not
exceed 56 VDC (a 48 volt plant on boost charge). However, I've
seen subscriber line carrier systems that used 75 volts! And of
course that odd circumstance has to be designed for.

How about loop extenders, such as Lorain made? Didn't some raise
the loop voltage to get more talk level on Farmer Brown's line?

That's a good example. And these kinds of devices may not be
common, but in some places they aren't rare.

The 400 ohms value is unlikely to be the battery resistance
either. Originally that was a typical value when line current,
sensed by a "line relay", was supplied through two windings of a
polar (balanced) relay. The typical line relay had 200 ohms DC
resistance per winding.

Today the loop current is often regulated, and hence the
effective series resistance can be almost anything. Different
manufacturers regulate at different loop currents, usually from
25 to 45 milliamps, so the range of values is all over the map.
Particularly because, again with equipment like subscriber line
carrier and loop extenders, the loop current might be as high as
120 milliamps, though the original recommendation was to not
exceed half that.

Telephone loops vary greatly. Moreover, several specs say
something to the effect that 95% of the plant should meet a
given criteria. The point being that an impaired, but
functional, telephone line is allowed when that is the only
possible way to provide service to Granny out on the Farm.

--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com