| Author |
Message |
James Knott
Guest
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 Posted:
Thu Apr 28, 2005 7:27 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | I'm not going to look that up to be certain, but I don't think
it is correct. T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
|
10baseT was designed to run on the same cat 3 cable as was used to wire
phone systems. The whole idea was that offices had lots of the stuff.
| Quote: | Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable.
The frequency has little to do with whether it will interfere.
The voltage level is what makes a difference. Besides, 10baseT
does not run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Which is to say that VF circuits and 10baseT do in fact share
the same frequency range for the entire VF range.
|
Where shall I start. Lessee now...
10baseT uses Manchester encoding, where there's one complete cycle per bit,
with the phase inverted for a "1" bit in the data. So, if you had a steady
"1" or a steady "0", you'd see a continuous 10 MHz square wave, which has a
fundamental frequency of 10 MHz, plus harmonics. An alternating "1 0" bit
pattern would result in a fundamental frequency of 5 MHz, plus harmonics.
Every other bit pattern would fall between those extremes. I doubt you'd
see frequencies anywhere near the voice frequencies and DC is impossible,
as the lines are transformer coupled. So the highest voice frequency would
be in the vicinity of 4 KHz and the lowest ethernet frequency around 5 MHz
or over 1000x greater. I'd be surprised, if much voice energy made it
through the transformers. As for voltage, it won't make much difference,
unless great enough to cause physical damage, considering any voice signal
is well removed from the frequencies used by ethernet and likely to be
blocked by the transformers. |
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Tomi Holger Engdahl
Guest
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| Posted:
Thu Apr 28, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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floyd@barrow.com (Floyd L. Davidson) writes:
| Quote: | James Knott <james.knott@rogers.com> wrote:
DaveC wrote:
Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing
noise between these two.
Yes, it's entirely acceptable. When twisted pair ethernet was created, it
was intended to be run on existing cat 3 telephone cables, along side phone
lines.
I'm not going to look that up to be certain, but I don't think
it is correct. T1 was certainly designed for telephone lines,
|
Yes.
| Quote: | but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
|
10BASE-T was designed to operate on early Cat-3 UTP wiring.
At the time 10Base-T was standardized there was not such
thing as CAT5 wiring! At the time the 10Base-T system was
started to be deployed on larger scale (somewhere in the
beginnignof 1990's) there was no such thign as CAT5
(maybe some cable vendors have dreamed on this and worked
on standard, but nothign on market). At that time all that
was available was CAT3 and CAT4 wiring. In know installations
made at that time that used CAT4 for telephone outlets and CAT4
for data.
| Quote: | Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable.
The frequency has little to do with whether it will interfere.
The voltage level is what makes a difference.
|
Frequency has a lot to quite much on the interferences.
Most communications systems are designed to be frequency
sensitive, so that they effectively receive the signals
only on the range they operate at, the signals at other
frequencies gets very much attenuated before they get
into the receiving electronics. This means that signal
outside normal operating range needs to be considerably
higher in amplitude (compared to signal at operating frequency
range) to cause harmdul interfence.
| Quote: | Besides, 10baseT does *not* run at 10Mbps...
that is merely the highest bit rate.
|
10Base-T pushes bits to the line at fixed 10Mbps rate.
It either sends but out at that rate, or not (is silence
when not transmitting).
| Quote: | The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Which is to say that VF circuits and 10baseT do in fact share
the same frequency range for the entire VF range.
|
10Base-T does not use / need the DC to 15 MHz frequency range.
10Base-T does not use DC signals to anything. All the
10Base-T Ethernet equipment are transformer coupled to the
line, which means that none of then are capable of sending
out DC to the line and they can't receive signal DC level.
All the data sent to line is manchester coded, free of any
DC component. This means that the frequency range of 10Base-T
Ethernet does not start form DC. The practical frequency
range of signal you cna find on line definately lies
between few hundred kHz to 30 MHz, where the most
signal energy lies between 5 MHz and 10 MHz frequency range.
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
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Tomi Holger Engdahl
Guest
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| Posted:
Thu Apr 28, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
|
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DaveC <me@privacy.net> writes:
| Quote: | Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing noise
between these two.
|
The UTP Ethernet "standard" before 10Base-T was called StarLan
and it was specifically designed to have telephone signals and
1 Mbit/s Ethernet on the same cable terminated to RJ-45 connectors.
The 10Base-T system was an officially standardized faster version
of this. In the design of 10Base-T it was designed so that the
signal can travel trough the telephone wires, and can travel
through the same cables that carry also telephone signals.
10Base-T and PSTN telephone on the same CAT5 cable works.
This kind of arrangement might not be up to the newest cabling
recommendations / standards, but it works.
In modern system it is a pain in the neck to wire two different
signals to one connector at both ends since all the termination
equipment (typically RJ-45 jacks) is designed generally with one
jack-one cable paradigm in mind. I think that modern standards say
that you are not supposed to share horizontal cable between
applications. But sharing osa same cable will work with 10Base-T.
The is not much crosstalk between different pairs on CAT5 wiring
and 10Base-T is very robust system (with sitable filters it is
possible to even run 10Base-T signals and normal telephone signals
on the same wire pair, there are products that do this).
Sharing the cable between telephone and some faster Ethernet standard
might be more problematic, because those tend to be more sensitive
to the noise and some implementations use more wire pairs.
100Base-TX when run with telephone might still work but there
coudl be reaiabity problems. You can't run 1000Base-T with any
other signals, because gigabit Ethernet on copper use all
of the four wire pairs in CAT5 wire.
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/ |
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Morten Reistad
Guest
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| Posted:
Thu Apr 28, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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|
In article <lajll73wihd.fsf@solarflare.cs.hut.fi>,
Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:
| Quote: | DaveC <me@privacy.net> writes:
Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing noise
between these two.
[snip] |
| Quote: | This kind of arrangement might not be up to the newest cabling
recommendations / standards, but it works.
In modern system it is a pain in the neck to wire two different
signals to one connector at both ends since all the termination
equipment (typically RJ-45 jacks) is designed generally with one
jack-one cable paradigm in mind. I think that modern standards say
that you are not supposed to share horizontal cable between
applications. But sharing osa same cable will work with 10Base-T.
|
I have done this professionally for a long time. The cabling is designed
for multi-purpose use. The only downside is you have to follow specifications
with some exactness when you use it this way.
The pairs are as follows :
Pair Colours Pins
1 Blue/White 4-5
2 Green/White 3-6
3 Orange/White 1-2
4 Brown/White 7-8
Ethernet uses pair 2-3. (pins 3-6,1-2). Maximum distance 100m.
ISDN BRI's uses pair 1 for the U("outdoors") interface (pins 4-5)
and pair 1+2 for the S and T interfaces ("indoors"). (pins 4-5,3-6)
Max distance 6km for U, 1000m for T, 100m for S.
ISDN PRI's uses pair 1 and 3 (pins 1-2,4-5). Maximum distance 400m.
POTS use pair 1. pins 4-5. Maximum distance 6km.
Anything carrying high (er) voltages to the end user equipment is
reserved for pair 1, pin 4-5.
Living in Europe, I never got much experience with T1's. Perhaps
someone can fill in T1 use of cat5 here.
I try to never mess with installed cabling, and only use "doctored"
patch cables when I want to do splitted interfaces. Makes it a little
easier for others to discover what is going on. As other have remarked,
the system is designed to have clever things done in patch cables, not
inside installed wiring.
Also, colours tagging are used for unusual cables, although I haven't
seen this standardized. What seems to be a common denominator is
White, Grey, Black : Ethernet straight cables
Yellow : Ethernet, crossed cables
Red : POTS or ISDN BRI (sometimes crossed ethernet)
Green : POTS or ISDN BRI
Blue : ISDN PRI
| Quote: | The is not much crosstalk between different pairs on CAT5 wiring
and 10Base-T is very robust system (with sitable filters it is
possible to even run 10Base-T signals and normal telephone signals
on the same wire pair, there are products that do this).
Sharing the cable between telephone and some faster Ethernet standard
might be more problematic, because those tend to be more sensitive
to the noise and some implementations use more wire pairs.
|
| Quote: | 100Base-TX when run with telephone might still work but there
coudl be reaiabity problems. You can't run 1000Base-T with any
other signals, because gigabit Ethernet on copper use all
of the four wire pairs in CAT5 wire.
|
I haven't seen this as a problem, except on long ISDN PRI runs.
The ISDN PRI runs a 2 Mhz signal, and is pretty strong, and can
do havoc with an Ethernet in the same cable.
-- mrr |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 2:29 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Floyd L. Davidson wrote:
I'm not going to look that up to be certain, but I don't think
it is correct. T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
10baseT was designed to run on the same cat 3 cable as was used to wire
phone systems. The whole idea was that offices had lots of the stuff.
|
CAT1 is telephone grade UTP. There was no significant amount of
CAT3 cable in a telephone office at the time 10baseT was
designed, and in fact there still isn't.
There just is no use for CAT3 cable in a telephone office other
than for 10baseT. Runs of T1/DS1 between racks in the same row
could use it, but it doesn't have a ground wire, so it isn't
used. Any runs of T1/DS1 between rows requires what is called
ABAM, which is shielded twisted pair. For voice pairs CAT3
could be used, but CAT1 is sufficient and is less expensive.
CAT3 was designed for data networks, not telephone networks.
| Quote: | Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable.
The frequency has little to do with whether it will interfere.
The voltage level is what makes a difference. Besides, 10baseT
does not run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Which is to say that VF circuits and 10baseT do in fact share
the same frequency range for the entire VF range.
Where shall I start. Lessee now...
10baseT uses Manchester encoding, where there's one complete cycle per bit,
with the phase inverted for a "1" bit in the data. So, if you had a steady
"1" or a steady "0", you'd see a continuous 10 MHz square wave, which has a
fundamental frequency of 10 MHz, plus harmonics. An alternating "1 0" bit
pattern would result in a fundamental frequency of 5 MHz, plus harmonics.
|
Yes. I was thinking of NRZ or AMI as is used in T1/DS1
encoding. The point is still the same though, because the
frequency is *not* what interfers. It's the voltage.
The spectrum for 10baseT has 5 and 10 Mhz fundamental
components, and typically would have significant 15 and 30 Mhz
3rd harmonic components (which are unnecessary for proper
operation).
| Quote: | Every other bit pattern would fall between those extremes.
|
You are, like I was, thinking of how NRZ works.
With Manchester coding "every other bit pattern" is merely a
combination of one or the other of the two extremes. *Every*
bit has a transition, which is the 5 Mhz component. Any change
from either a 1 to an 0, or from a 0 to a 1, results in a 10 Mhz
component by adding a transition between the regular once per
bit transition.
| Quote: | I doubt you'd
see frequencies anywhere near the voice frequencies and DC is impossible,
as the lines are transformer coupled. So the highest voice frequency would
be in the vicinity of 4 KHz and the lowest ethernet frequency around 5 MHz
or over 1000x greater.
|
That is true, and certainly is a characteristic that has
significance; but it doesn't mean that crosstalk from 20 Hz ring
current cannot interfere with the the 10baseT receiver. It
merely limits the mechanics of what can happen.
| Quote: | I'd be surprised, if much voice energy made it
through the transformers.
|
Same as for ring current, except that since the levels are
significantly lower it is very unlikely that any VF signals
actually will cause interference.
| Quote: | As for voltage, it won't make much difference,
unless great enough to cause physical damage, considering any voice signal
is well removed from the frequencies used by ethernet and likely to be
blocked by the transformers.
|
There can be and often are high frequency components in the ring
current, and since we are talking about an extremely high level
signal by comparison, the levels that would interfere can be
present. Note that the exact same cable problems can result in
problems from "60Hz" power influence too, which might also have
significant components at higher frequencies (for both telephone
and power cabling it is not uncommon to see spikes on the cable
that are in the 1 GHz frequency range).
The significant point though, for this type of problem, is that
it would be very intermittant and would probably not produce
errors at a rate sufficient to even be noticed.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Carl Navarro
Guest
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| Posted:
Thu Apr 28, 2005 2:38 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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On Wed, 27 Apr 2005 18:15:12 -0800, floyd@barrow.com (Floyd L.
Davidson) wrote:
| Quote: | Rich Seifert <usenet@richseifert.com.invalid> wrote:
floyd@barrow.com (Floyd L. Davidson) wrote:
T1 was certainly designed for telephone lines,
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
10BASE-T was designed to operate on early Cat-3 UTP wiring. This was
better than untwisted (quad-type) telephone wire, or "silver satin"
modular phone cords. Cat-5 wiring was designed for 100 Mb/s operation.
CAT3 is not "telephone" cable though. Twisted pair telephone
cable is CAT1, useful up to relatively 1 MHz. (A 1.544 Mbps
rate of a T1 has a maximum required frequency bandwidth of 750
KHz, and works just fine on CAT1.)
CAT2 cable was designed for 4Mbps Token Ring and is useful up to
1.5MHz. CAT3 was designed 10Mbps 10baseT, and is useful up to
16 MHz. CAT4 for 20 Mbps (meant for 16Mbps token ring) or
20MHz. CAT5 for 100Mbps 100baseTX and useful up to 100MHz.
The point is still that 10baseT was not designed to work over
telephone cable.
|
I guess "cat-1" was Quad/Paper/Lead cable with random twists (being
kind to quad for the twist part).
| Quote: | Besides, 10baseT
does *not* run at 10Mbps... that is merely the highest bit
rate. The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
The spectrum used by 10baseT is 5 to 10 MHz. Which makes CAT3
cable a relatively conservative choice... and CAT5 is simply
overkill, but then again I don't even know if anyone stocks CAT3
cable these days!
|
Of course they do. I just unloaded 20K feet of the stuff in 2 motels.
It went well with the 18K of Cat-5e and 15K of RG6 and that was only
in the walls.
BTW and ot Has anyone tried the Hellerman/Tyton jacks? The T-568B is
natively straight color code and the pairs terminate together.
RJ-25's still keep the pairs together but blue/green/orange order.
About the same price as Leviton's and they fit Lev keystones.
Carl Navarro |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 3:04 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Tomi Holger Engdahl <then@solarflare.cs.hut.fi> wrote:
| Quote: | floyd@barrow.com (Floyd L. Davidson) writes:
James Knott <james.knott@rogers.com> wrote:
DaveC wrote:
Is it acceptable to use 1 pair in a Cat-5 cable for POTS when 2 pair are
being used for 10base-T? Wondering about cross-talk, etc., introducing
noise between these two.
Yes, it's entirely acceptable. When twisted pair ethernet was created, it
was intended to be run on existing cat 3 telephone cables, along side phone
lines.
I'm not going to look that up to be certain, but I don't think
it is correct. T1 was certainly designed for telephone lines,
Yes.
but I don't think 10baseT was. Look at the difference in the
twist on CAT5 compared to lesser grade twisted pair!
10BASE-T was designed to operate on early Cat-3 UTP wiring.
|
The intent is juxtapositioned. CAT3 cable was designed for
10baseT, and allows VF circuits to ride on the two unused pairs.
| Quote: | At the time 10Base-T was standardized there was not such
thing as CAT5 wiring! At the time the 10Base-T system was
started to be deployed on larger scale (somewhere in the
beginnignof 1990's) there was no such thign as CAT5
(maybe some cable vendors have dreamed on this and worked
on standard, but nothign on market). At that time all that
was available was CAT3 and CAT4 wiring. In know installations
made at that time that used CAT4 for telephone outlets and CAT4
for data.
|
True, but the typical *telephone* cable was CAT1 quality, not
CAT3 (and higher) until 10baseT came along.
| Quote: | Also, the frequencies used on telephones are nowhere near those
used by ethernet, so interference is unlikely. I've even seen
installations, where two 100 Mb ethernet circuits share one cable.
The frequency has little to do with whether it will interfere.
The voltage level is what makes a difference.
Frequency has a lot to quite much on the interferences.
|
We are discussing systems which encode voltage levels, not
frequency or phase. By definition "noise" is a unwanted voltage
change, and the frequency or phase of the change is
insignificant. Only on systems where frequency or phase is used
for encoding or modulation would that be defined as noise.
However, frequency relates to the ability to *transport* the
signal, even though it is the voltage level which actually
causes interference.
If the frequency is such that it will not pass through various
parts of the transmission path, there will likely be
insufficient voltage at a point (the receiver) where it can
cause a problem. But if the voltage is sufficient, it makes no
difference what frequency it is.
| Quote: | Most communications systems are designed to be frequency
sensitive, so that they effectively receive the signals
only on the range they operate at, the signals at other
frequencies gets very much attenuated before they get
into the receiving electronics. This means that signal
outside normal operating range needs to be considerably
higher in amplitude (compared to signal at operating frequency
range) to cause harmdul interfence.
|
At the point where it enters the system. But at the point where
it actually interferes with the intended signal, frequency is
insignificant.
| Quote: | Besides, 10baseT does *not* run at 10Mbps...
that is merely the highest bit rate.
10Base-T pushes bits to the line at fixed 10Mbps rate.
It either sends but out at that rate, or not (is silence
when not transmitting).
|
See the various discussion articles on Manchester coding and
frequency spectrum. The bit rate is indeed fixed at 10 Mbps,
but that does *not* necessarily translate directly to a 10 MHz
bandwidth or a 10 MHz fundamental. In the case of Manchester
coding only (others are distinctly different) it means a 5 MHz
bandwidth that ranges from 5 to 10 MHz. (Other components are
generated at 15 and 30 MHz, but are not required at the receiver
for proper operation.)
| Quote: | The actual frequency spectrum runs from DC on up through
at least 15 Mhz (three times the 5 Mhz fundamental for 10 Mbps).
Which is to say that VF circuits and 10baseT do in fact share
the same frequency range for the entire VF range.
|
I was thinking about NRZ encoding, not Manchester. Sorry about
that.
| Quote: | 10Base-T does not use / need the DC to 15 MHz frequency range.
10Base-T does not use DC signals to anything. All the
10Base-T Ethernet equipment are transformer coupled to the
line, which means that none of then are capable of sending
out DC to the line and they can't receive signal DC level.
All the data sent to line is manchester coded, free of any
DC component. This means that the frequency range of 10Base-T
Ethernet does not start form DC. The practical frequency
|
True.
| Quote: | range of signal you cna find on line definately lies
between few hundred kHz to 30 MHz, where the most
signal energy lies between 5 MHz and 10 MHz frequency range.
|
Virtually *all* essential spectral components are at 5 and 10
MHz. The transmitter may generate a square wave, but the
receiver only requires a sine wave, therefore none of the other
components have significance at the receiver (or anywhere else).
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 3:07 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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David Lesher <wb8foz@panix.com> wrote:
| Quote: | James Knott <james.knott@rogers.com> writes:
Given the great difference in frequencies used, how is cross-talk an issue.
Ringing is generally 20 Hz and voice is less than 4 KHz, whereas ethernet
is up around 5 - 10 MHz (for 10 Mb ethernet).
Simple; ringing is 300+ V peak to peak...
|
And could very easily have components at 1GHz!
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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James Knott
Guest
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| Posted:
Thu Apr 28, 2005 4:10 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | David Lesher <wb8foz@panix.com> wrote:
James Knott <james.knott@rogers.com> writes:
Given the great difference in frequencies used, how is cross-talk an
issue. Ringing is generally 20 Hz and voice is less than 4 KHz, whereas
ethernet is up around 5 - 10 MHz (for 10 Mb ethernet).
Simple; ringing is 300+ V peak to peak...
And could very easily have components at 1GHz!
|
Harmonics at 1 GHz from a 20 Hz signal???? That would be the 50 millionth
harmonic! Not likely. And the usual method of measuring AC voltage is
"RMS", not peak to peak. Even still, if there was significant crosstalk of
the ringing current, it's nowhere near frequencies used by ethernet. You
could place that ringing current directly on the ethernet pair and it
wouldn't have much effect. Incidentally, for many years, communications
companies routinely placed both current loop data (up to about 100 b/s) on
the same pair as was used for voice. There was rarely any interference,
even though the frequency difference is much less than that with ethernet. |
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James Knott
Guest
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| Posted:
Thu Apr 28, 2005 4:14 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | CAT3 is not "telephone" cable though. Twisted pair telephone
cable is CAT1, useful up to relatively 1 MHz. (A 1.544 Mbps
rate of a T1 has a maximum required frequency bandwidth of 750
KHz, and works just fine on CAT1.)
|
Cat 3 has been in common use for many years. Incidentally, many years ago,
I used to buy that stuff many kilometres at a time.
Lessee now. We have you, who's obviously short a few facts, making that
claim and Rich, who helped design ethernet is making the opposite claim.
Who should we believe? |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Floyd L. Davidson wrote:
CAT3 is not "telephone" cable though. Twisted pair telephone
cable is CAT1, useful up to relatively 1 MHz. (A 1.544 Mbps
rate of a T1 has a maximum required frequency bandwidth of 750
KHz, and works just fine on CAT1.)
Cat 3 has been in common use for many years. Incidentally, many years ago,
I used to buy that stuff many kilometres at a time.
|
How long ago is "many years", relative to the introduction of
10baseT?
| Quote: | Lessee now. We have you, who's obviously short a few facts, making that
claim and Rich, who helped design ethernet is making the opposite claim.
|
Rich did *not* make any such opposite claim.
| Quote: | Who should we believe?
|
Since we agree, it seems obvious enough...
Rich pointed out two things, both of which are correct. One is
that 10baseT was designed for CAT3 cable. The other was that I
described the 10baseT spectrum as if it were NRZ encoding, and
in fact it is Manchester coding.
*You* are the one who claims that 10baseT was designed to work
on "telephone cable", which is a description that applies to
CAT1 cable. CAT3 didn't even exist as a cable specification
until just before 10baseT was released. CAT3 came first, but it
was to allow data networking such as 10baseT to happen.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Floyd L. Davidson
Guest
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| Posted:
Thu Apr 28, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James, why to you continue trying to redirect this thread to
only one newsgroup? That is rude.
James Knott <james.knott@rogers.com> wrote:
| Quote: | Floyd L. Davidson wrote:
David Lesher <wb8foz@panix.com> wrote:
James Knott <james.knott@rogers.com> writes:
Given the great difference in frequencies used, how is cross-talk an
issue. Ringing is generally 20 Hz and voice is less than 4 KHz, whereas
ethernet is up around 5 - 10 MHz (for 10 Mb ethernet).
Simple; ringing is 300+ V peak to peak...
And could very easily have components at 1GHz!
Harmonics at 1 GHz from a 20 Hz signal???? That would be the 50 millionth
harmonic! Not likely.
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Who said anything about harmonics?
| Quote: | And the usual method of measuring AC voltage is
"RMS", not peak to peak.
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RMS has no meaning when applied to such things as spikes or harmonic
content. Peak to peak is appropriate for impulse noise that interferes
with something like an ethernet receiver.
| Quote: | Even still, if there was significant crosstalk of
the ringing current, it's nowhere near frequencies used by ethernet.
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It doesn't have to be. Frequency is *not* what determines whether
it will interfere or not.
| Quote: | You
could place that ringing current directly on the ethernet pair and it
wouldn't have much effect.
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Please cite the specs for a form of ethernet where the receiver
can handle +/- 300 volt burst of random noise hits.
| Quote: | Incidentally, for many years, communications
companies routinely placed both current loop data (up to about 100 b/s) on
the same pair as was used for voice. There was rarely any interference,
even though the frequency difference is much less than that with ethernet.
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"Current loop data" at 100bs that doesn't interfere with voice?
You're leaving something out. If you would like an example of
that, just pick up any phone that has a tone/pulse switch, and
switch it to pulse. Give it a try and see if you think 10 pps
is not interfering.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Robert Redelmeier
Guest
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| Posted:
Thu Apr 28, 2005 11:17 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
| Quote: | It doesn't have to be. Frequency is *not* what determines
whether it will interfere or not.
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Then what does? Voltage? Far enough apart, frequencies
don't interfere. Do you have trouble understanding speech
on an elevator ride? Both are changes in air pressure,
but at ~100,000x different frequency.
| Quote: | You could place that ringing current directly on the ethernet
pair and it wouldn't have much effect.
Please cite the specs for a form of ethernet where the
receiver can handle +/- 300 volt burst of random noise hits.
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Ethernet transceivers are designed for 500V isolation.
AFAIK, ringing voltage is 90V max P-P (still above LV specs!).
Capacitive effects cause very little crosstalk. Most is from
induction. Current matters, not voltage.
Ethernet is differential signalling which further isolates
noise. I haven't tested, but a phone ring to a modern set may
not even spoil a single ethernet packet inside a shared sheath.
Easy enough to test with a flood ping.
-- Robert |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 6:54 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | Simple; ringing is 300+ V peak to peak...
And could very easily have components at 1GHz!
Harmonics at 1 GHz from a 20 Hz signal???? That would be the 50 millionth
harmonic! Not likely.
Who said anything about harmonics?
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Well, we were talking about ringing current which is normally 20 Hz. You
said it could have "components" at 1 GHz. What could those components be,
if not harmonics. Incidentally, harmonics require some non-linear
compontent, to distort a sine wave (a perfect sine wave does not have
harmonics). Ringing generators may not produce perfect sine waves, but I'd
be very surprised, if they produced measurable amounts of energy at 1 GHz.
| Quote: | RMS has no meaning when applied to such things as spikes or harmonic
content. Peak to peak is appropriate for impulse noise that interferes
with something like an ethernet receiver.
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I thought we were talking about ringing current. A ringing current is
simply a 90 volt RMS sine wave at 20 Hz. It does not normally produce
noise or spikes of comparable amplitude.
| Quote: | It doesn't have to be. Frequency is not what determines whether
it will interfere or not.
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If the ethernet receivers are not sensitive to 20 Hz ringing or the normal
telephone voice frequencies (< 4 KHz) it will not cause interference. It
would take an enormously powerful signal in the audio range to have much
effect on ethernet.
| Quote: | Please cite the specs for a form of ethernet where the receiver
can handle +/- 300 volt burst of random noise hits.
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Perhaps Rich can provide the relevant specs, but ethernet cards must, for
safety reasons be able to sustain such voltages, without creating a safety
hazard. However, normal telephone ringing and voice does not produce a
300V burst of random noise hits. Now lets get down to some technical
details. As I mentioned in another note, the energy for 10 Mb ethernet is
largely confined to the range of 5 - 10 MHz. The line transformers and
other circuitry will be optimized for that frequency range. That range is
also more than 1000x greater than the highest frequencies expected in a
telephone circuit. With that much difference in frequency, it's a trivial
matter to filter out signals as far removed from the ethernet signal as
voice or ringing. If those items are not able to reach the ethernet
signal, how are they supposed to interfere???
| Quote: | "Current loop data" at 100bs that doesn't interfere with voice?
You're leaving something out. If you would like an example of
that, just pick up any phone that has a tone/pulse switch, and
switch it to pulse. Give it a try and see if you think 10 pps
is not interfering.
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Use split winding transformers, to couple the data line to the voice line.
The two halves of the split winding are connected at voice frequencies, by
capacitors, to bypass the data line. That capacitor appears as a high
impedance to the data circuit. The data currents through the two halves of
the windings are such that they cancel out any interference they might
otherwise cause.
Here's a crude drawing. The "X" represents the capacitor
__________ ________________ Combined voice and data
) (_________
Voice ) _X______ Data
_________ ) (________________
In the above, the voice circuit enters from the left. The data is on the
inside pair at the right and the line to the far end is on the outside at
right. The capacitor is selected to be a low impedance at voice
frequencies and high impedance at data frequencies. This circuit will be
repeated at the other end.
When you click the hook switch or use pulse dial, you're actually opening an
closing the voice circuit, as those switch contacts are wired in series
with the voice path. |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 6:57 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Robert Redelmeier wrote:
| Quote: | AFAIK, ringing voltage is 90V max P-P
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Actually, it's 90V RMS, or about 255V P-P. |
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