| Author |
Message |
David Lesher
Guest
|
 Posted:
Mon May 02, 2005 2:28 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
floyd@barrow.com (Floyd L. Davidson) writes:
| Quote: | You just happen to work only with data services that arbitrarily
use high rates. What about a 7 baud circuit? Or even a 45.5
baud circuit?
|
A 45.5 baud 130 mA circuit maybe, Floyd? With an KSR 28
on the end....
| Quote: | 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.
|
Huh?
| Quote: | That is not true. Almost all outside cable plant is twisted
pair. (Though not quite all, only because some relatively short
runs of drop wire are non-twisted.) I don't know that today
there are any remaining runs of 1 mile or more using open wire
line...
|
I agree with Floyd here. Only butt-ugly 2 conductor drop
is untwisted. And I don't know that Ma even uses it anymore..
[pulp]
| Quote: | All of it on twisted pair. That is significantly distinct from
silver satin, which is not twisted pair.
|
If you think pulp cable is not twisted, you've got some manhole
[OOPS "maintenance hatchway"] time coming. All that lead-sheathed
cable is quite twisted. [A local crew just cut 600' of ~1200 pair
pulp out and replaced it with icky-pic. I stopped and chatted several
times. The MH was so cramped they were doing only 100 pairs a day....]
| Quote: | It is not hardly "marginal", it is *vastly* better.
Well barbed wire works fine too, as long as there are no
external fields to induce interference.
.....
Of course there are very few examples of locations where that is
the case, given that today almost any telephone service is where
there are AC power distribution services too.
|
Take a battery-power scope and go find a field far enough away from
the grid that you can not see 60Hz on a 10' long antenna...
--
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 |
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Floyd L. Davidson
Guest
|
| Posted:
Mon May 02, 2005 6:11 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
Robert Redelmeier <redelm@ev1.net.invalid> wrote:
| Quote: | 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?
|
I hope not to have been less than pedantic about *anything* in
this thread! The entire discussion has been pedantic from the
start. What's your point?
I try to be pedagogic too, but you and James Knott are very
difficult to instruct!
| Quote: | Voice is nowhere near data
in frequency. So the truism of idential impairments has
no practical effect.
|
That is simply *not* true. What is or not "data" does not
equate to frequency in any way. "Voice" distinctly defines a
relative ranges of bandwidths, but "data" does not.
You just happen to work only with data services that arbitrarily
use high rates. What about a 7 baud circuit? Or even a 45.5
baud circuit?
(To be pedantic, I'm assuming above that by "data" you meant
"digital data", because in fact "voice" is one form of "analog
data". ;-)
| Quote: | 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.
|
That is not true. Almost all outside cable plant is twisted
pair. (Though not quite all, only because some relatively short
runs of drop wire are non-twisted.) I don't know that today
there are any remaining runs of 1 mile or more using open wire
line...
Other than various kinds of two pair drop wire there are *no*
multi-pair cables that are non-twisted. (Though there are at
least two non-twisted conductors in every cable, but I'll leave
the purpose and use of those as an exercise for the reader.)
| Quote: | 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.
|
All of it on twisted pair. That is significantly distinct from
silver satin, which is not twisted pair.
| Quote: | 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.
|
It is not hardly "marginal", it is *vastly* better.
I should probably also remark specifically on the idea that
marginal effects can make a large difference for digital
services. The opposite is true. Digital is immune to many
"marginal" impairments, which is specifically the reason todays
telecommunications networks are virtually all digital. The SNR
of the data remains high (hence the error rate low)) despite
changes of marginal impairments (such as the facility SNR), with
the additional significance that the "noise" is not additive
(multi-link circuits have an end to end SNR equal to the highest
individual link SNR rather than the ratio of the signal to the
sum the noise from all links, as it would be with analog
facilities).
That is vitally important to the design and implementation of
telecom facilities. Because the error rate remains low (even
when the SNR change is *far* from "marginal") it is possible to
use m-ary (multilevel) encoding schemes that trade SNR for
bandwidth to achieve greater capacity. That is, for example,
the essence of V.90 digital modem protocols compared for example
to V.34 analog modem protocols!
| Quote: | 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
|
Of course there are very few examples of locations where that is
the case, given that today almost any telephone service is where
there are AC power distribution services too.
| Quote: | in a shared sheath isn't much problem, although it will pick
|
One split pair in a shared sheath can only be a non-problem as I
noted above... in an environment where there is no external
field. That means, for a multi-pair cable, that it effectively is
*always* a problem if any other pairs are used.
In fact however, external fields are not the only problem with
split pairs. That is merely the only cause of induced noise.
Longitudinal imbalance will result in increased transmission
losses too, which are frequency dependent and as the frequency
in use increases that can be a fatal impairment too. Which of
course is true for either digital or analog uses.
| Quote: | 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.
|
You do know what a split pair is? It *always* involves two
pairs. Whether both of those pairs are used is of little
consequence in a cable with other active pairs.
The data *will* care. How much depends; but given any
significant distance or external induction the effects will be
quite significant.
| Quote: | 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)
|
"Under some circumstances" means nothing, because under an equal
number of other circumstances the opposite would be just a true.
| Quote: | 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.
|
That is a foolish statement. At 6' there is little risk. At
12' there is significant risk. At 50' it is pure folly, but
sometimes luck makes it work (while you watch, and then it fails
when you aren't there).
| Quote: | 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.
|
Of course you can "push it through". But what you can't do is
install that and walk away with any confidence at all that it
will continue to work. The question is not if there will be a
failure, but is merely a matter of how long until something
causes it to fail. That is why there are standards and why
installation to standards has advantage. It *continues* to
work, even when other factors change at a later date.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Floyd L. Davidson
Guest
|
| Posted:
Mon May 02, 2005 8:14 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
David Lesher <wb8foz@panix.com> wrote:
| Quote: | floyd@barrow.com (Floyd L. Davidson) writes:
You just happen to work only with data services that arbitrarily
use high rates. What about a 7 baud circuit? Or even a 45.5
baud circuit?
A 45.5 baud 130 mA circuit maybe, Floyd? With an KSR 28
on the end....
|
Yeah! Been there and done that one, eh? :-)
| Quote: | 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.
Huh?
|
I think he's talking about drop wire. I know GTE used to
use non-twisted pair drop wire in a lot of places. I always
thought it was a damned fool idea, but...
....
| Quote: | Well barbed wire works fine too, as long as there are no
external fields to induce interference.
....
Of course there are very few examples of locations where that is
the case, given that today almost any telephone service is where
there are AC power distribution services too.
Take a battery-power scope and go find a field far enough away from
the grid that you can not see 60Hz on a 10' long antenna...
|
Used to drive GTE right up the walls...
Back in the early 80's I worked on Eielson AFB, south of
Fairbanks, and most of the time they had a humongus 1800 Hz tone
induced into every pair on the base. We did eventually
determine the exact source, but were not able to get it fixed.
The base power plant had one particular generator that produced
it. If that generator was on line, it was everywhere.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Robert Redelmeier
Guest
|
| Posted:
Mon May 02, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
| Quote: | I hope not to have been less than pedantic about *anything*
in this thread! The entire discussion has been pedantic
from the start. What's your point?
|
Pedantic is not usually considered desireable. This discussion
started with a very simple question to which I and others said
"It's OK so long as you don't split a pair".
| Quote: | Robert Redelmeier <redelm@ev1.net.invalid> wrote:
Voice is nowhere near data in frequency. So the truism of
idential impairments has no practical effect.
That is simply *not* true. What is or not "data" does not
equate to frequency in any way. "Voice" distinctly defines
a relative ranges of bandwidths, but "data" does not.
|
Please see the Subject: line for a precise definition of the
data & voice we are discussing. I maintain my point that these
vastly differing frequencies (aided by balanced signalling)
greatly reduces the _effect_ of interference.
| Quote: | That is not true. Almost all outside cable plant is
twisted pair. (Though not quite all, only because some
relatively short runs of drop wire are non-twisted.)
I don't know that today there are any remaining runs of 1
mile or more using open wire line...
|
Newer cable most certainly has some twist. Older cable was
more rolled as a bundle(s) than twisted pairs. The roll
helps against external fields (60 cycle hum) but doesn't
help crosstalk.
| Quote: | 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.
It is not hardly "marginal", it is *vastly* better.
|
Certainly vastly at 10baseT (and moreso at 100baseTX),
but the difference is much less at ADSL freq.
| Quote: | I should probably also remark specifically on the idea that
marginal effects can make a large difference for digital
services. The opposite is true. Digital is immune to many
"marginal" impairments, which is specifically the reason
todays telecommunications networks are virtually all digital.
The SNR of the data remains high (hence the error rate low))
despite changes of marginal impairments (such as the facility
SNR), with the additional significance that the "noise" is
not additive (multi-link circuits have an end to end SNR
equal to the highest individual link SNR rather than the
ratio of the signal to the sum the noise from all links,
as it would be with analog facilities).
|
Yes, quite true. The downside of digital is less discussed.
When the error rate significantly exceeds the design BER,
then the whole thing fails entirely. Think of a BER of 0.1%
on TCP/IP. A split pair on 10baseT often causes less.
| Quote: | One split pair in a shared sheath can only be a non-problem
as I noted above... in an environment where there is no
external field. That means, for a multi-pair cable, that
it effectively is *always* a problem if any other pairs
are used.
|
We are talking a single POTS circuit and 10baseT two
pairs inside a single sheath. See the OP.
| Quote: | In fact however, external fields are not the only problem
with split pairs. That is merely the only cause of induced
noise.
|
External fields are not the only cause of induced noise. Crosstalk
is very severe in a split pair cable, and governs many 10/100
systems. It's what causes longer lengths of Cat3 to fail in
100baseTX.
| Quote: | Longitudinal imbalance will result in increased transmission
losses too, which are frequency dependent and as the frequency
in use increases that can be a fatal impairment too.
|
Longitudinal imbalance? A split pair is nowhere near as bad
as putting raw signal (no baluns) across coax as you cited.
The impedence of the shield is hardly specified, and even
the signal pathlength and velocity of propagation (slew)
will be different. Yet you reported it worked over 150'.
The impedence of a split pair will be off quite a bit, but
at least both splits will be the same if they're against
similar (grounded/floating) conductors.
| Quote: | You do know what a split pair is? It *always* involves
two pairs. Whether both of those pairs are used is of
little consequence in a cable with other active pairs.
|
Of course I know what split pairs are. I like to say:
"Electrons may be color blind, but they know who their
dance (twist) partners are." And obviously splitting pairs
involves more than one pair.
Consider the classic newbie goof -- RJ45 with pairs in
sequence. pins1&2 are paired and 10baseT in one direction
runs fine. Pins3&6 are split so the other direction is full
of errors (may not fail at 10, but most likely will at 100).
But if POTS has been put where it usually is (4&5), this pair
is also split, but against the ethernet split! I'd have to
double check the Left Hand Rule, but I believe this doesn't
cancel but amplifies crosstalk.
| Quote: | That is a foolish statement. At 6' there is little risk.
At 12' there is significant risk. At 50' it is pure folly,
but sometimes luck makes it work (while you watch, and then
it fails when you aren't there).
|
Folly? It's been working fine for a year, even with
considerable flex. It can now be easily fixed, but
there's just no real driver until it fails.
| Quote: | The question is not if there will be a failure, but is merely
a matter of how long until something causes it to fail.
That is why there are standards and why installation to
standards has advantage. It *continues* to work, even when
other factors change at a later date.
|
Of course it's a failure risk. But people have a right to take
informed risks. Standards are good and should be followed,
but sometimes the cost of complaince is greater than the
risk-adjusted cost of failure.
-- Robert |
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Dan Lanciani
Guest
|
| Posted:
Mon May 02, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
In article <d54397$pll$1@reader1.panix.com>, wb8foz@panix.com (David Lesher) writes:
| I agree with Floyd here. Only butt-ugly 2 conductor drop
| is untwisted. And I don't know that Ma even uses it anymore..
Verizon here in MA used it for my ISDN drops, but then they'll try almost
anything to make ISDN fail...
Dan Lanciani
ddl@danlan.*com |
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Morten Reistad
Guest
|
| Posted:
Mon May 02, 2005 3:01 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
In article <d54397$pll$1@reader1.panix.com>,
David Lesher <wb8foz@panix.com> wrote:
| Quote: | floyd@barrow.com (Floyd L. Davidson) writes:
Take a battery-power scope and go find a field far enough away from
the grid that you can not see 60Hz on a 10' long antenna...
|
Wasn't that 60 Hz interference a problem when doing field measures
from the moon; they had to wait until North America and Europe was
out of view?
-- mrr |
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James Knott
Guest
|
| Posted:
Mon May 02, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
Morten Reistad wrote:
| Quote: | Wasn't that 60 Hz interference a problem when doing field measures
from the moon; they had to wait until North America and Europe was
out of view?
|
I'd have though 50 Hz would have been the problem, when Europe was in
view. ;-) |
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Mark Evans
Guest
|
| Posted:
Mon May 02, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
In comp.dcom.cabling Robert Redelmeier <redelm@ev1.net.invalid> wrote:
| Quote: | 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.
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
|
Multipair telephone cable is twisted pair, nowhere near
the level of twist you'd find with data cable though.
The only non twisted pair you are likely to find on the
telco side is old single circuit drop wires.
| Quote: | wire is even worse, with even paper insulation. Yet hundreds of
|
There isn't anything wrong with paper as an insulator.
Though typically you have to use compressed air to
keep water out if the outer jacket springs a leak.
| Quote: | millions of circuits all work fine over thousands of feet per run.
|
--
Mark Evans
St. Peter's CofE Aided School
Phone: +44 1392 204764 X109
Fax: +44 1392 204763 |
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James Knott
Guest
|
| Posted:
Mon May 02, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
David Lesher wrote:
| Quote: | A 45.5 baud 130 mA circuit maybe, Floyd? With an KSR 28
on the end....
|
Actually, they were likely 60 mA or 20 mA. Incidentally, I started my
career overhauling teletypes. I worked on M32, M33, M28 & M35, among
others and my first computer printer was a M35 ASR, which I bought surplus
from my employer. |
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Floyd L. Davidson
Guest
|
| Posted:
Mon May 02, 2005 9:23 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
Robert Redelmeier <redelm@ev1.net.invalid> wrote:
| Quote: | In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
I hope not to have been less than pedantic about *anything*
in this thread! The entire discussion has been pedantic
from the start. What's your point?
Pedantic is not usually considered desireable. This discussion
started with a very simple question to which I and others said
"It's OK so long as you don't split a pair".
|
When you have people arguing technical details they don't
understand, pedantic attention to *correct detail* is extremely
important. Hence, while it may be true that pedantic is not
usually considered desirable, in this thread it has been
essential.
| Quote: | Robert Redelmeier <redelm@ev1.net.invalid> wrote:
Voice is nowhere near data in frequency. So the truism of
idential impairments has no practical effect.
That is simply *not* true. What is or not "data" does not
equate to frequency in any way. "Voice" distinctly defines
a relative ranges of bandwidths, but "data" does not.
Please see the Subject: line for a precise definition of the
data & voice we are discussing.
|
The subject line does *not* provide a definition for either data
or voice. 10baseT and POTS are specific, not general, forms of
each. If you want to say 10baseT and POTS, say it. Regardless,
*you* have discussed several other forms of data in this thread.
(Such word games are exactly why it is necessary to be pedantic.)
Regardless, you are still wrong. The impairments are the same,
all that differs is the intensity; and understanding the
mechanism, which is the "truism", is important.
| Quote: | I maintain my point that these
vastly differing frequencies (aided by balanced signalling)
greatly reduces the _effect_ of interference.
|
It does. And in a properly installed and functioning example
the interference will be below the critical point, and the
circuits will be deemed to be functional. However, saying, for
example, that 20 Hz ringing on a different pair will not be a
problem in such a circuit is vastly different than saying 20 Hz,
because it is on a different frequency, can't ever interfere
with 10baseT.
| Quote: | That is not true. Almost all outside cable plant is
twisted pair. (Though not quite all, only because some
relatively short runs of drop wire are non-twisted.)
I don't know that today there are any remaining runs of 1
mile or more using open wire line...
Newer cable most certainly has some twist. Older cable was
more rolled as a bundle(s) than twisted pairs. The roll
helps against external fields (60 cycle hum) but doesn't
help crosstalk.
|
Total nonsense.
The cable pairs are twisted. In fact each pair in a bundle
has a _different_ twist, to prevent any two of them from
getting too cozy. Then the whole bundle of twisted pairs
is swirled. And then all of the bundles are swirled within
the sheath itself. That is the way multi-pair cables have
been manufactured for many many decades.
Most power influence *is* crosstalk, between a comm cable and a
power cable. Anything that helps one will help with 60 Hz will
also help at VF and above, and as we've both noted previously
the effects are greater at higher frequencies. Which means it
is exceedingly difficult to do something which helps at 60 Hz
and does not have an even greater effect at VF or above.
| Quote: | Of course twisted pair is better. Expecially an EMI noisy
environment. But the difference is marginal. With digital,
marginal effects can make large differences.
It is not hardly "marginal", it is *vastly* better.
Certainly vastly at 10baseT (and moreso at 100baseTX),
but the difference is much less at ADSL freq.
|
Regardless, even at VF twisted pair is *vastly* better than flat
satin non-twisted cable. It is not a "marginal" difference.
| Quote: | I should probably also remark specifically on the idea that
marginal effects can make a large difference for digital
services. The opposite is true. Digital is immune to many
"marginal" impairments, which is specifically the reason
todays telecommunications networks are virtually all digital.
The SNR of the data remains high (hence the error rate low))
despite changes of marginal impairments (such as the facility
SNR), with the additional significance that the "noise" is
not additive (multi-link circuits have an end to end SNR
equal to the highest individual link SNR rather than the
ratio of the signal to the sum the noise from all links,
as it would be with analog facilities).
Yes, quite true. The downside of digital is less discussed.
When the error rate significantly exceeds the design BER,
then the whole thing fails entirely. Think of a BER of 0.1%
on TCP/IP. A split pair on 10baseT often causes less.
|
Nonsense. I don't even know where to start correcting that,
because none of it makes sense.
When the error rate significantly exceeds the design BER, what
happens is... the error rate exceeds the design BER. That
doesn't cause a catastrophic failure. Typically a progressively
higher BER will cause some degradation of the data throughput
for certain types of protocols, TCP being one. IP may or may
not be much affected... which is to say the effects on UDP will
be different than the effects on TCP. That is because UDP is
not a "reliable" protocol (and thus will be greatly affected)
and TCP is (and will merely be slowed down).
A BER of 0.1% strikes me as exceedingly high, given that the
target on DS1 facilities is 1 x 10e5, and you are talking 100
times that. Given that most DS1 facilities run more like 10e8,
or another thousand times less, I'd say that a split pair
causing a 1x10e3 BER is in *extremely* bad repair.
| Quote: | One split pair in a shared sheath can only be a non-problem
as I noted above... in an environment where there is no
external field. That means, for a multi-pair cable, that
it effectively is *always* a problem if any other pairs
are used.
We are talking a single POTS circuit and 10baseT two
pairs inside a single sheath. See the OP.
|
What I said is still true and what you said was not.
If you split a pair using CAT3 or CAT5 for 10baseT or 100baseTX,
there *is* going to be a problem. A short length measured in
feet will work with 10baseT, but for 100baseTX it will be
measured in inches. Both are necessarily the multi-pair example
I described above, with or without a POTS circuit present.
| Quote: | In fact however, external fields are not the only problem
with split pairs. That is merely the only cause of induced
noise.
External fields are not the only cause of induced noise. Crosstalk
is very severe in a split pair cable, and governs many 10/100
systems. It's what causes longer lengths of Cat3 to fail in
100baseTX.
|
Crosstalk *is* an external field.
| Quote: | Longitudinal imbalance will result in increased transmission
losses too, which are frequency dependent and as the frequency
in use increases that can be a fatal impairment too.
Longitudinal imbalance? A split pair is nowhere near as bad
as putting raw signal (no baluns) across coax as you cited.
|
It is *exactly* the same thing at the end of the cable where a
differential detector is expected to make use of common mode
rejection.
| Quote: | The impedence of the shield is hardly specified, and even
|
So?
| Quote: | the signal pathlength and velocity of propagation (slew)
will be different.
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Exactly. And that will lead to both phase and amplitude
distortion which differs between the two wires of the pair, and
that results in amplitude distortion for the facility as a
whole.
| Quote: | Yet you reported it worked over 150'.
|
For an ADSL loop. Do you understand that no doubt means
that a similar length of CAT3 with a split pair stretched
out in the same place would work equally well?
| Quote: | The impedence of a split pair will be off quite a bit, but
at least both splits will be the same if they're against
similar (grounded/floating) conductors.
|
So? It might be, but it might not be.
| Quote: | You do know what a split pair is? It *always* involves
two pairs. Whether both of those pairs are used is of
little consequence in a cable with other active pairs.
Of course I know what split pairs are. I like to say:
"Electrons may be color blind, but they know who their
dance (twist) partners are." And obviously splitting pairs
involves more than one pair.
|
Then why were you babbling about having only one pair involved?
| Quote: | Consider the classic newbie goof -- RJ45 with pairs in
sequence. pins1&2 are paired and 10baseT in one direction
runs fine. Pins3&6 are split so the other direction is full
of errors (may not fail at 10, but most likely will at 100).
But if POTS has been put where it usually is (4&5), this pair
is also split, but against the ethernet split! I'd have to
double check the Left Hand Rule, but I believe this doesn't
cancel but amplifies crosstalk.
|
More nonsense.
Wired that way there are two split pairs, period. Whether POTS
is put on the second split pair or not will make little
difference to the 10baseT using a split pair. Putting POTS on
*any* pair, split or otherwise, in that cable is going to be a
problem for the 10baseT signal on the split pair. Which is to
say, if the pair is split, *any external field* will induce a
current and cause problems.
I have no idea what nonsense you are referencing in regard to
a Left Hand Rule and crosstalk cancellation vs. amplification.
And I hate to think what it is you mean...
| Quote: | That is a foolish statement. At 6' there is little risk.
At 12' there is significant risk. At 50' it is pure folly,
but sometimes luck makes it work (while you watch, and then
it fails when you aren't there).
Folly? It's been working fine for a year, even with
considerable flex. It can now be easily fixed, but
there's just no real driver until it fails.
|
It is pure folly. Abject foolishness. (Am I clear enough?? :-)
My bet is that you have no idea whether is works well or not!
I saw a guy "splice" some CAT5 once. It was a 175' or so run
and at about 125 feet the roll ran out. So he got another
roll and literally tied the two cables physically together
with a knot and then split out each pair and twisted the wires
together and taped them up, and finished the run.
It "worked"! I told him, as did a couple other people, that
is was too ugly to live and that he ought to be shot. Not
to mention that I didn't believe that it worked anyway.
You know, it "worked" just fine. The PC it went to could access
the LAN. What can one say, eh? There was this nagging problem
that that PC for the next 6 months would hang, sometimes several
times a day. And when IT tried to work on it remotely they
usually could, and nothing would be wrong, and sometimes couldn't
get into it at all.
We finally got fed up and found someone with the authority and
the understanding of cable, showed him that splice and he
"authorized" the culprit to run another cable for that PC.
On an Ethernet, particularly using IP, it is relatively
difficult to know just how bad some of these things actually
are...
| Quote: | The question is not if there will be a failure, but is merely
a matter of how long until something causes it to fail.
That is why there are standards and why installation to
standards has advantage. It *continues* to work, even when
other factors change at a later date.
Of course it's a failure risk. But people have a right to take
informed risks.
|
Exactly. David Lesher and I both had comments previously about
doing exactly that. But given the strange ideas you have about
how all of this works, I can't see what you are doing as an
"informed" risk.
| Quote: | Standards are good and should be followed,
but sometimes the cost of complaince is greater than the
risk-adjusted cost of failure.
|
No doubt.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Mark Evans
Guest
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| Posted:
Tue May 03, 2005 4:12 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
|
In comp.dcom.cabling Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:
| Quote: | What the typical telephone cable indide house is depends on the
country and the year when the building is built. Some countries
|
Not even that is a good guide. Since an installation may have
been made long after the building was constructed. Especially
with overhead drop wires. If it looks like an old piece of
cable is causing problems it's going to get replaced by more
modern cable.
| Quote: | recommended better cabling than CAT1 on 1980's for example to
be prepared to future technologues (ISDN at that time).
Some of the cable installed to offices and residential buildings
from 1980's on has been pretty high quality (CAT3 rating or almost
like it). I know the situation in Finland best. I wrote one
paper for one course at Helsinki University of technology on ISDN
technology (around 1995), and when writing on that I read quite carefully
one publication from Helsinki telephone company that described
the suitablility of existing wirings for ISDN use.. gave idea
|
Both ISDN and ADSL are specifically designed to run over existing
cabling. It would be incredibly expensive to have to replace all the
underground multicore.
| Quote: | what kind of cable was use on buildings in the last decade or two..
|
--
Mark Evans
St. Peter's CofE Aided School
Phone: +44 1392 204764 X109
Fax: +44 1392 204763 |
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