| Author |
Message |
James Knott
Guest
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 Posted:
Fri Apr 29, 2005 7:10 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
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?
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.
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.
|
10baseT was early 90's. I don't have a date handy for cat 3, but cat 6 & 7
were being planned in 1997.
<http://www.connectek.net/pages/cat6_history.htm>
<http://www.commserv.ucsb.edu/infrastructure/standards/history/wiring_standards_standards.asp> |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 7:15 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | 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.
|
I was buying large quantities of cat 3 in 1989 for voice and data circuits
in central office and customer premise applications. There was a lot of it
in service back then. Ethernet is early '90s.
| Quote: | 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.
|
Draw it out. You'll see that an alternating 1 0 pattern will have a
fundemental frequency of 5 MHz or 1/2 that of a steady 1 or 0.
| Quote: | 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.
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.
|
If the ethernet circuits are design to operate in the 5 - 10 MHz range,
there won't be much effect from < 4 KHz. |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 7:21 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | The intent is juxtapositioned. CAT3 cable was designed for
10baseT, and allows VF circuits to ride on the two unused pairs.
|
"CAT 3" refers to a quality standard, not number of pairs. While 4 pairs is
commonly used for ethernet, 25 pairs is used in central offices to connect
24 circuit channel banks etc. 50 pair cable is also often used. Modern
home have 3 pair cat 3 for phone wiring. There are many other
configurations available.
| Quote: | True, but the typical telephone cable was CAT1 quality, not
CAT3 (and higher) until 10baseT came along.
|
As I mentioned in other notes, I was buying, in my work, large quantities of
cat 3 cable in 1989, which (IIRC) predates twisted pair ethernet. |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 7:28 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | How long ago is "many years", relative to the introduction of
10baseT?
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I started buying it in 1989 and it had been in common use for many years
before then. Ethernet over twisted pair is (IIRC) early '90s.
| 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.
|
You said:
"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!"
Rich said:
"10BASE-T was designed to operate on early Cat-3 UTP wiring."
| Quote: | Who should we believe?
Since we agree, it seems obvious enough...
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From where I sit, it looks like you disagree. See the above quotes. |
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Tomi Holger Engdahl
Guest
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| Posted:
Fri Apr 29, 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:
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?
|
For example in Finland the telephone wiring recommendation book
"Puhelinsisävekkokirja 1989" recommended residential building
internal telephone network beign wired with MHS 3 pair wiring or similar.
Also cable MHS 1 x 4 x 0,5 was used in the 1980's.
Those cables are approximately CAT3 in their rating.
Also the VMOHBU cable used in buried cable installation is sufficient
for Ethernet use according what I have read on the topic.
| Quote: | 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.
|
Maybe the official CAT3 definition was did not come long
before 10Base-T ethernet, but the cables meeting this
specification had been made and installed years earlier
than that. At least on some countries.
--
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:
Fri Apr 29, 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: |
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.
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.
|
What the typical telephone cable indide house is depends on the
country and the year when the building is built. Some countries
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
what kind of cable was use on buildings in the last decade or two..
In Finland some people are using the old telephone wiring to run
10Base-T or 100Base-TX Ethernet on them for networking purposes.
There is information on that at http://www.helsinkiopen.net/
At some countries there has been practice to install higher
quality cable, and some used the cheapest you can get
(I have see some installations in Russia and i doub that
if they world even qualify even as CAT1).
| Quote: | 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.
|
True.
| Quote: | 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.)
|
True.
| Quote: | Virtually *all* essential spectral components are at 5 and 10
MHz. The transmitter may generate a square wave,
|
The transmitted signal on 10Base-T is essentially square wave
with some pre-distortion added to it and then filtered through
the low pass filter that revoves all highest frequency components
(so that system passes the noise limits on above 30 MHz noise).
So the the signal from 10Base-T transmitter can be viewed as
slightly distorted swuare wave signal.
| Quote: | but the
receiver only requires a sine wave, therefore none of the other
components have significance at the receiver (or anywhere else).
|
--
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:
Fri Apr 29, 2005 8:20 am Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Robert Redelmeier <redelm@ev1.net.invalid> writes:
| Quote: | In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
It doesn't have to be. Frequency is *not* what determines
whether it will interfere or not.
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.
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.
Ethernet transceivers are designed for 500V isolation.
|
10Base-T Ethernet transceivers and Ethernet cards are typically
designed with around 1500V isolation.
That 500V isolation level was used on Ethernet that used
coaxial cable.
| Quote: | 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.
|
I have not found any ring signal relared problems for Ethernet
at tests where I have had 10Base-T and PSTN line signal
on a shared sheath. I have not made any wide tests on this though..
I have even tested application where you put normal telephone
signals and Ethernet signals on the same wire pair.
Just two small capacitors for block DC + attenuate low frequencies
for Ethernet input/output. And then a suitable low pass
filter for telephone line signals input/output.
Worked at least on laboratory setup without problems
for 10Base-T Ethernet. No packet loss because of
ring current... On hook/off hook situation and
pulse dialling were more challenging signals for
this setup, but di dnot cause great problems either.
The setup was like this (idea from Petri Krohn):
Computer Ethernet(Tx)
/----||---------
/ /---||---------
CO ________ / / ________
----|LPfilter|----/----~~~--/-/--|LPfilter|----
----|________|---/-/---~~~---/---|________|----
/ / Telephone equipment
----------||---/ /
----------||----/
Ethernet switch (Rx)
Ethernet switch (Tx) Computer Ethernet(Rx)
_______________________________________________
_______________________________________________
--
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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Floyd L. Davidson
Guest
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| Posted:
Fri Apr 29, 2005 2:51 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:
How long ago is "many years", relative to the introduction of
10baseT?
I started buying it in 1989 and it had been in common use for many years
before then. Ethernet over twisted pair is (IIRC) early '90s.
|
Try 1991 for CAT3.
You didn't buy it in 1989. (CAT1 is a classification that appeared in
1985 though... :-)
| 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.
You said:
"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!"
|
Can you actually read. "designed for telephone lines, but I
don't think 10basetT was." *Telephone lines*.
| Quote: | Rich said:
"10BASE-T was designed to operate on early Cat-3 UTP wiring."
|
CAT3 is data network cable. CAT1 is "telephone lines".
| Quote: | Who should we believe?
Since we agree, it seems obvious enough...
From where I sit, it looks like you disagree. See the above quotes.
|
Looks more like you just don't have a decent set of facts to go on,
and perhaps have a reading disability.
--
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:
Fri Apr 29, 2005 3:00 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:
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?
For example in Finland the telephone wiring recommendation book
"Puhelinsisävekkokirja 1989" recommended residential building
internal telephone network beign wired with MHS 3 pair wiring or similar.
Also cable MHS 1 x 4 x 0,5 was used in the 1980's.
Those cables are approximately CAT3 in their rating.
Also the VMOHBU cable used in buried cable installation is sufficient
for Ethernet use according what I have read on the topic.
|
Yes, the point is they did *not* recommend CAT3 in the 1980's.
| Quote: | 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.
Maybe the official CAT3 definition was did not come long
before 10Base-T ethernet, but the cables meeting this
specification had been made and installed years earlier
than that. At least on some countries.
|
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.
T1/DSX-1 equipment, on the other hand, was designed to use
"telephone lines"... However, the only "telephone" grade cable
it is normally put on is outside plant cable. Inside plant will
be on ABAM, not CAT3.
--
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:
Fri Apr 29, 2005 3:03 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Robert Redelmeier wrote:
AFAIK, ringing voltage is 90V max P-P
Actually, it's 90V RMS, or about 255V P-P.
|
Actually, it is up to 120 V RMS. Which is 297 V P-P.
Typicical ring generators actually produce 90 to 105 V RMS.
--
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:
Fri Apr 29, 2005 3:48 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Robert Redelmeier <redelm@ev1.net.invalid> wrote:
| Quote: | In comp.dcom.cabling Floyd L. Davidson <floyd@barrow.com> wrote:
It doesn't have to be. Frequency is *not* what determines
whether it will interfere or not.
Then what does? Voltage?
|
The parameter that is modulated or encoded is the only parameter
which suffers interference.
Hence if you have an FM system, changes in the frequency will be
"noise", and changes in the amplitude will not have an effect.
But if you are encoding (as is typical on a wire line circuit)
the amplitude of the voltage, then its frequency is not
significant but any undesired change in amplitude is "noise".
(Note that I am using a rather broad definition of "noise",
which is why I've quoted it. Technically noise is an external
influence that is not inherent to the channel, and undesired
internal change is "distortion". The difference is that
distortion is a quantifiable parameter of the channel and with
enough bandwidth it can be corrected, which cannot be done with
noise.)
| Quote: | Far enough apart, frequencies
don't interfere.
|
That is because there are frequency sensitive components in the
transmission path that reduce the *voltage* of the noise.
Essentially, voltage noise can be filtered out *if* it has some
other parameter that allows you to selectively reduce its level
while not affecting the desired signal level.
And the same applies in systems which encode or modulate some
parameter other than voltage. For example in an FM system the
voltage differences are commonly filtered out by limiting
amplifiers, which removes most of the frequency interference if
the voltage levels are sufficiently distinct! Same as we are
discussing with 10baseT, except "frequency" and "voltage" are
reversed as to which is signal and noise and which is the
"other" parameter that can be filtered.
| Quote: | Do you have trouble understanding speech
on an elevator ride? Both are changes in air pressure,
but at ~100,000x different frequency.
|
See above... same effects, same differences.
| 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.
Ethernet transceivers are designed for 500V isolation.
|
Isolation for *what*? Breakdown, where arcing occurs is one thing,
but blocking the receiver is another. The isolation rating has
no relationship to the dynamic range of the receiver input. And
regardless of the dynamic range, it simply makes *no difference*
what the frequency of the voltage is at the input to the receiver.
| Quote: | AFAIK, ringing voltage is 90V max P-P (still above LV specs!).
|
Ring voltage is commonly 90-105 *RMS*. It is allowed to be as
high as 120 VAC RMS.
| Quote: | Capacitive effects cause very little crosstalk. Most is from
induction. Current matters, not voltage.
|
Current causes induction. The field induced results in a *voltage*
being detected at the receiver (otherwise, it doesn't exist!).
That is why 10baseT, and similar protocols, are designed for
roughly 100 ohm cable, rather than say 2000 or 20000 ohm cable.
| Quote: | Ethernet is differential signalling which further isolates
|
Which is the reason it uses twisted pair, which provides high
common mode rejection of induced noise.
| Quote: | 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.
|
Inside a shared sheath that is properly wired yes, and that is
*exactly* what the specifications are intended to provide. The
point here was originally stated as what the effect will be if
there are kinks or other damage to the cable or miswired
connectors that split a pair.
When you talk about using a facility that has greater than 60 dB
common mode rejection and use the functional parameters to
suggest that therefore a directly connected burst of 250-300 P-P
ring current at 20 Hz won't be a problem, it is not logically
valid.
The 10baseT receiver can handle 20 Hz voltage when it is first
reduced more than 60 dB by common mode rejection and then an
additional 20-40 dB by the high pass nature of the transformers
used. The resulting voltage reaching the receiver is
significantly lower than the desired signal. But if the "more
than 60 dB" from common mode rejection is not there, that
voltage is serious competition for the desired signal,
regardless of what frequency it is.
--
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:
Fri Apr 29, 2005 3:56 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | AFAIK, ringing voltage is 90V max P-P
Actually, it's 90V RMS, or about 255V P-P.
Actually, it is up to 120 V RMS. Which is 297 V P-P.
Typicical ring generators actually produce 90 to 105 V RMS.
|
Where'd the 120V come from? Phone ring generators are nominally 90V, as you
then say in the last line. |
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James Knott
Guest
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| Posted:
Fri Apr 29, 2005 4:02 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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Floyd L. Davidson wrote:
| Quote: | Inside a shared sheath that is properly wired yes, and that is
*exactly* what the specifications are intended to provide. The
point here was originally stated as what the effect will be if
there are kinks or other damage to the cable or miswired
connectors that split a pair.
|
Who was asking about damaged cable? The original question was about running
phone and ethernet over the same cable. |
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Floyd L. Davidson
Guest
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| Posted:
Fri Apr 29, 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: |
Where'd the 120V come from? Phone ring generators are nominally 90V, as you
then say in the last line.
|
The specifications.
--
Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@barrow.com |
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Rich Seifert
Guest
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| Posted:
Fri Apr 29, 2005 4:20 pm Post subject:
Re: 10base-T & POTS in same Cat-5 cable? |
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|
In article <87d5sdx0b2.fld@barrow.com>,
floyd@barrow.com (Floyd L. Davidson) wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
Floyd L. Davidson wrote:
I'd say that a 300 volt P-P signal is in fact "an enormously
powerful signal", compared to the desired signal, wouldn't you?
Please cite the specs for a form of ethernet where the receiver
can handle +/- 300 volt burst of random noise hits.
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.
So, you can't cite any spec to support what you've said.
Off hand I don't know what the dynamic range of the receiver
input is, but the desired signal is a maximum of 2.8 V P-P, so I
can't imagine that the dynamic range is required to be much more
than twice that. However, it should also be clear that *any
voltage* greater than 1.4 V at the receiver input is going to
absolutely interfere with the ability of the receiver to detect
a valid crossover in the desired signal.
|
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.
There is no specification for the maximum differential voltage that must
be sustainable across a 10BASE-T receiver input, although clearly:
-It must be able to sustain (and decode) a maximum-amplitude transmitted
signal, which is 2.8 V peak. (IEEE 802.3 section 14.3.1.2.1.)
-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).)
As to tolerance of traditional telephony signals inadvertently presented
to a 10BASE-T receiver, the standard notes the following:
-Battery voltage is generally 56 Vdc applied through 400 ohms.
-Ringing voltage has an AC component of up to 175V peak at 20-60 Hz
through a 100 ohms source impedance (on top of the battery voltage).
As to what might occur if there was a wiring error, the standard says:
"Although 10BASE-T equipment is not required to survive [much less
operate during] such wiring hazards without damage, application of any
of the above voltages shall not result in any safety hazard." (IEEE
802.3 section 14.2.7.4.)
That is, putting a ring signal across a 10BASE-T receiver may cause the
receiver to be permanently destroyed, but it should not be a safety
hazard, i.e., cause personal injury.
Most 10BASE-T receivers put a pair of back-to-back zener diodes across
the input, which clamp voltages far in excess of the expected signal
levels. However, if the source impedance of the high input voltage is
low enough (i.e., there is enough *energy* available), the zener diodes
will be destroyed by the clamping current, followed by the destruction
of most of the rest of the input circuitry. Puffs of smoke and faint
smells of burning carbon resistors may follow.
--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX
Send replies to: usenet at richseifert dot com |
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