| Author |
Message |
James Knott
Guest
|
 Posted:
Tue Sep 06, 2005 9:47 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
David Lesher wrote:
| Quote: |
The far bigger issue is.. the phone line goes outside...
and it brings in Murphy's messenger -- lightning...
You may like lightning on your LAN....I'll pass.
|
While lightning may be a concern, when was the last time you had a hit that
damaged any equipment? Though I have lost a couple of pieces to problems
to power line problems, I can't recall ever losing anything to lightning,
certainly nothing connected to the phone line. Also, if you've got an ADSL
or dialup connection, you're connected to the phone lines. Many others are
on cable modems. Why don't they cause lightning problems? Incidentally,
many years ago, I worked as a technician for a telecommunications company.
I recall many storms, where I could watch the gas tube protectors flashing
(connected to open wire lines), but there was no damage to the equipment,
beyond burned carbons. Phone lines have protectors on them and short of a
very close hit, you'll not likely have damage. Have you *EVER* had to
replace a phone that was damaged by lightning? And yes, I have seen damage
caused by a direct hit to a radio tower. One side of a cross connect block
looked perfectly normal. The other side, didn't have any pins left on it.
Just lots of burn marks and little copper balls on the floor! Also, in
Toronto, is the CN Tower, which is over 1800 feet tall. That tower
regularly takes lightning hits. Yet, the equipment I was responsible for
up there managed to keep on running, despite all the lightning strikes.
Lightning can certainly be a risk, but proper protection eliminates much of
that risk. If you take a direct hit, you've got a lot more things to worry
about, than your computer. |
|
| Back to top |
|
 |
Robert Redelmeier
Guest
|
| Posted:
Tue Sep 06, 2005 11:01 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> wrote:
| Quote: | While lightning may be a concern, when was the last time
you had a hit that damaged any equipment? Though I have
lost a couple of pieces to problems to power line problems,
I can't recall ever losing anything to lightning, certainly
|
I lose ports occasionally, and I'm not entirely sure
what fried them, even though I don't have any outdoor wire.
| Quote: | nothing connected to the phone line. Also, if you've got
an ADSL or dialup connection, you're connected to the phone
lines. Many others are on cable modems. Why don't they
cause lightning problems?
|
Because both cable and phone service entrances have grounded
protection.
| Quote: | in Toronto, is the CN Tower, which is over 1800 feet tall.
That tower regularly takes lightning hits. Yet, the
equipment I was responsible for up there managed to keep
on running, despite all the lightning strikes.
|
Of course. The CN Tower certainly has carefully, custom
designed lightening protection. Proper grounding and caging
for equipment areas.
-- Robert |
|
| Back to top |
|
|
Robert Redelmeier
Guest
|
| Posted:
Tue Sep 06, 2005 11:14 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> wrote:
| Quote: | 100baseT signaling is at 125 Mbaud. You'd have to generate
some incredible harmonic levels to get interference at
|
Harmonics? We aren't talking carrier-wave! All it takes is
a single spike to ruin one bit, then the 12 kbit packet is shot.
| Quote: | those frequencies. You mentioned pulse dialing. When you
have a square wave, the amplitude of the harmonics decreases
with the inverse of the harmonic, so, if you take the 10th
|
Induction works by rate of change of current. A square
wave has an extremely high rate of change, so induces lots
of current. Think point/coil automobile ignitions. TP cable
is somewhat like a coil but without the turn ratio or high
output impedence to build voltage.
| Quote: | Here's an experiment you can try. Connect a 100baseT
ethernet through a 100M long CAT5 cable. Then place
continuous ringing current on one spare pair and continuous
dial pulses on the other spare pair. Then measure your
frame errors, compared to when there's no ringing & dialing.
|
I'd expect no trouble from ringing current, and little drom
dialing on a modern electronic phone (they probably cannot
generate really sharp pulses). But an old mechanical dialer
might be a different story. I think a guy from Finland posted
with his tests.
-- Robert |
|
| Back to top |
|
|
Jack Masters
Guest
|
| Posted:
Wed Sep 07, 2005 2:45 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott wrote:
| Quote: | David Lesher wrote:
The far bigger issue is.. the phone line goes outside...
and it brings in Murphy's messenger -- lightning...
You may like lightning on your LAN....I'll pass.
While lightning may be a concern, when was the last time you had a hit that
damaged any equipment? Though I have lost a couple of pieces to problems
to power line problems, I can't recall ever losing anything to lightning,
certainly nothing connected to the phone line.
|
Guess you are lucky enough to have the phone lines buried deep enough.
We have to deal with 90% of the lines being overhead, and I have seen
plenty fried phones and modems. The telco here by default installs a
symbolic protection unit (overvoltage between the wires), but nothing to
ground. Insurance companies don't even bother to query a 'modem struck
by ligtning' claim, as there are so many of them in summer. |
|
| Back to top |
|
|
David Ross
Guest
|
| Posted:
Wed Sep 07, 2005 1:23 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
| Quote: | While lightning may be a concern, when was the last time you had a hit that
damaged any equipment? Though I have lost a couple of pieces to problems
to power line problems, I can't recall ever losing anything to lightning,
certainly nothing connected to the phone line. Also, if you've got an ADSL
or dialup connection, you're connected to the phone lines. Many others are
on cable modems. Why don't they cause lightning problems? Incidentally,
|
Protection is as much a matter of how the building / site is wired as it
is surge protection, grounding, etc...
After the 3rd $4000 hit and a lost 1/2 day of production I got
permission to track down some things in an office I support. Buildings
on the block are 90 year old converted warehouses. Power for this office
came in from pole through 2nd floor wall near ceiling then down to main
fuse panel on 1st floor then back up to 2nd floor distribution boxes.
Ground was on 1st floor. Nice looking wire going through the brick then
down into the sidewalk. No idea how deep it went after that. Street and
sidewalks have only been rebuild a dozen times or more over the life of
the building. Phone lines come into the SIDE of the building on 2nd
floor. Tracing them back, the are aerial across then alley then into the
next building. There the phone block (which actually looks abandoned) is
grounded to a water pipe. Plus there is a tie back to the power panel
for that space on the other side of the space. Grounding for that panel
is to a capped water pipe that goes into the next space. In that space
the water pipe also grounds a few more panels then goes down and out to
the street. Maybe ok. Start looking closely at the street and talking to
folks who've been there a while and the water pipes used for grounding
were disconnected 10 years ago and new water mains, meters, and lines
into the buildings were laid. But these new ones are NOT the ones used
for grounding.
The point? When you have multiple paths into a building that are tied
together via electronics you will get very high transient voltages with
nearby strikes. In incredibly simplistic terms think of the strike as
generating a wave in the pond. As long as everything ties to the pond at
one point, it all rises and falls together. But if you are attached at
separate physical points, one can be on the crest while the other is on
the valley. Wham!
Anyway, as a stop gap we put in fused links on the lines. Paired with
the first in the line being resettable with the 2nd being a pure fuse.
Plus we ran all the outside phone lines through a single connector block
and show the owners where to "pull the plug" when desired. They live in
another bay of the building and yes they do walk over and pull the plug
when awakened by a storm. And yes we are getting all the wiring and
grounding issues addressed. |
|
| Back to top |
|
|
Robert Redelmeier
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> wrote:
| Quote: | Even that "spike" can be analyzed into a series of
harmonics. Look up Fourier analysis .
|
I'm well aware of this. But harmonics are not necessary for
interference. Harmonics tend to persist and produce noise.
Digital baseband signalling is highly resistant to low level noise,
but will fail on very short spikes that wipe one bit. Fortunately,
higher protocol levels can take care of low error-rates.
| Quote: | Again, look at the harmonic content of the dial pulses.
You'll find no significant harmonic energy at the frequencies
used by ethernet.
|
There may be none in the signal itself, but induction transforms
signal energy. Again, I'm not talking about harmonics but about
single events, perhaps doubling on one previous reflected event.
-- Robert |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
Robert Redelmeier wrote:
| Quote: | Even that "spike" can be analyzed into a series of
harmonics. Look up Fourier analysis .
I'm well aware of this. But harmonics are not necessary for
interference. Harmonics tend to persist and produce noise.
Digital baseband signalling is highly resistant to low level noise,
but will fail on very short spikes that wipe one bit. Fortunately,
higher protocol levels can take care of low error-rates.
|
If we're talking about dial pulses interfering with ethernet, we're talking
about harmonics. As I mentioned, even those spikes are some sum of various
harmonics of something. What are the frequency components of those spikes?
Without doing the analysis, you can't say. What I can say with a high
degree of confidence, is that any spikes generated by some device attached
to a phone line, are unlikely to have any significant energy in the
frequency range used by ethernet. As I mentioned in a previous note,
ethernet signals are in the range of several MHz, with 100baseT running in
the vicinity of 125 megabaud, which has a fundamental frequency of 62.5
MHz. One thing that's been obvious for decades, as experienced with radio
communications, is that such impulse noise from electrical devices,
lightning etc., is virtually nonexistant at those frequencies. You will
not find any such interference from "spikes" at those frequencies.
| Quote: | Again, look at the harmonic content of the dial pulses.
You'll find no significant harmonic energy at the frequencies
used by ethernet.
There may be none in the signal itself, but induction transforms
signal energy. Again, I'm not talking about harmonics but about
single events, perhaps doubling on one previous reflected event.
|
The original claim was interference from the phone line. There are 3
desired signals on a phone line. The main one is voice, with energy
primarily below 4 KHz, 20 Hz ringing current and in some situations, pulse
dialing, typically at 10 or 20 pps. A pure sine wave has no harmonics.
Every other signal does. This means that everything on a phone line is
either a sine wave of the sum of a series of sine waves. There is no other
possibility.
Once you have determined the various frequencies involved, you can then
determine:
a) the coupling of those signals between pairs
and
b) any interfering effect of those signals on the desired signal.
Any other "conclusions" are simply nonsense.
| Quote: | There may be none in the signal itself, but induction transforms
signal energy. Again, I'm not talking about harmonics but about
single events, perhaps doubling on one previous reflected event.
|
Harmonics can only be generated when a signal passes through a non-linear
device. Inductive or capacitive coupling does not produce harmonics.
Semiconductors, corroded connections etc., do. But then you'd again have
to analyze the circuit, to determine what harmonics are likely and again,
the amplitudes from anything on a phone line are unlikely to produce
significant energy at the frequencies used by ethernet. |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
David Ross wrote:
| Quote: | Protection is as much a matter of how the building / site is wired as it
is surge protection, grounding, etc...
|
Quite so. I have also seen some bad installations. Any installation
connected to the outside world through wire, has to have a good ground
connection. A poor ground system is an open invitation for lightning
induced damage. However, to get back to my point, running phone lines
through an ethernet cable is no more of a risk than connecting the computer
to a modem. |
|
| Back to top |
|
|
Robert Redelmeier
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> wrote:
| Quote: | Precisely. That's why sharing an ethernet cable with a
protected phone line is no more risky than having a modem
connected to the computer.
|
Agreed. I wasn't saying shared sheath is dangerous to equipment,
just that some packets might get ruined from interference and
that shared sheath was designed around 10baseT, not 1`00baseTX.
| Quote: | The tower has three (IIRC) very heavy ground leads. In a
severe storm, they can glow red hot.
|
Uninsulated, obviously, but should have ceramic stand-offs.
I would think cooling would be an issue.
-- Robert |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
Jack Masters wrote:
| Quote: | While lightning may be a concern, when was the last time you had a hit
that
damaged any equipment? Though I have lost a couple of pieces to problems
to power line problems, I can't recall ever losing anything to lightning,
certainly nothing connected to the phone line.
Guess you are lucky enough to have the phone lines buried deep enough.
We have to deal with 90% of the lines being overhead, and I have seen
plenty fried phones and modems. The telco here by default installs a
symbolic protection unit (overvoltage between the wires), but nothing to
ground. Insurance companies don't even bother to query a 'modem struck
by ligtning' claim, as there are so many of them in summer.
|
While the cable are buried where I currently live (buried cables can also
have lighting induced problems), in the past I've lived in areas with
overhead lines. Also, many years ago, I used to work in Northern Ontario
(where I saw those flashing gas tubes) on systems connected to open wire
lines, where you've got pairs of wire, not cable, running for hundreds of
miles. The storms in that area were often very severe. One night, I
thought I saw some fluoresent lights flashing outside, during a storm.
When I looked the next morning, I discovered that those "lights" were in
fact power line insulators that were arcing over.
As for your area, what have they got against grounding? Lightning induced
surges are generally common mode, which a protector across the pair won't
protect against. |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
Robert Redelmeier wrote:
| Quote: | nothing connected to the phone line. Also, if you've got
an ADSL or dialup connection, you're connected to the phone
lines. Many others are on cable modems. Why don't they
cause lightning problems?
Because both cable and phone service entrances have grounded
protection.
|
Precisely. That's why sharing an ethernet cable with a protected phone line
is no more risky than having a modem connected to the computer.
| Quote: | in Toronto, is the CN Tower, which is over 1800 feet tall.
That tower regularly takes lightning hits. Yet, the
equipment I was responsible for up there managed to keep
on running, despite all the lightning strikes.
Of course. The CN Tower certainly has carefully, custom
designed lightening protection. Proper grounding and caging
for equipment areas.
|
The tower has three (IIRC) very heavy ground leads. In a severe storm, they
can glow red hot. The equipment room is in a Faraday cage, but that's to
prevent interference from all the TV & FM broadcast transmitters located on
the tower along with the microwave and VHF/UHF communications systems. |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Wed Sep 07, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
Robert Redelmeier wrote:
| Quote: | 100baseT signaling is at 125 Mbaud. You'd have to generate
some incredible harmonic levels to get interference at
Harmonics? We aren't talking carrier-wave! All it takes is
a single spike to ruin one bit, then the 12 kbit packet is shot
|
Any non-sinusoidal signal has harmonics. With a square wave (the simplest
case, the harmonic amplitudes are inversely proportional to the order of
the harmonic. Even that "spike" can be analyzed into a series of
harmonics. Look up Fourier analysis .
| Quote: | those frequencies. You mentioned pulse dialing. When you
have a square wave, the amplitude of the harmonics decreases
with the inverse of the harmonic, so, if you take the 10th
Induction works by rate of change of current. A square
wave has an extremely high rate of change, so induces lots
of current. Think point/coil automobile ignitions. TP cable
is somewhat like a coil but without the turn ratio or high
output impedence to build voltage.
|
Again, do a Fourier analysis. Any repetitive signal can be analyzed into a
series of sine waves. In the case of a 1 V square wave, it works out to a
1 volt sine wave at the fundemental frequency, 1/3 V at the 3rd harmonic,
1/5 V at the 5th, 1/7V at the 7th etc. Notice a pattern here? As you
increase increase in frequency, the harmonic amplitude is proportionally
smaller and smaller. Now with a 10 PPS dialing, you'd have to consider
harmonics up to the millionth and more, where the level of those harmonics
is going to be so low, that you won't be able to measure them through the
background noise.
| Quote: | Here's an experiment you can try. Connect a 100baseT
ethernet through a 100M long CAT5 cable. Then place
continuous ringing current on one spare pair and continuous
dial pulses on the other spare pair. Then measure your
frame errors, compared to when there's no ringing & dialing.
I'd expect no trouble from ringing current, and little drom
dialing on a modern electronic phone (they probably cannot
generate really sharp pulses). But an old mechanical dialer
might be a different story. I think a guy from Finland posted
with his tests.
|
Again, look at the harmonic content of the dial pulses. You'll find no
significant harmonic energy at the frequencies used by ethernet. |
|
| Back to top |
|
|
David Lesher
Guest
|
| Posted:
Wed Sep 07, 2005 9:35 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> writes:
| Quote: | Because both cable and phone service entrances have grounded
protection.
Precisely. That's why sharing an ethernet cable with a protected phone line
is no more risky than having a modem connected to the computer.
|
Which is a major risk.... I never ever use internal {PCI bus} modems.
An external modem w/ serial port gives you an excellent sacrificial
lamb to Murphy.
Induce a large spike onto the Ethernet pair on your machine, and
hope that the standoff insulation saves your butt.
If you think the protector the telco provides will save your Ethernet;
keep spares around. Using the same cable is like painting a bullseye
on your butt and going to Pamplona. It works, and you may be luckly
for a long time...but...
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433 |
|
| Back to top |
|
|
Robert Redelmeier
Guest
|
| Posted:
Wed Sep 07, 2005 11:16 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
James Knott <james.knott@rogers.com> wrote:
| Quote: | If we're talking about dial pulses interfering with ethernet,
we're talking about harmonics.
|
Why only harmonics? There are other kinds of interference.
| Quote: | that's been obvious for decades, as experienced with radio
communications, is that such impulse noise from electrical
devices, lightning etc., is virtually nonexistant at those
frequencies. You will not find any such interference from
"spikes" at those frequencies.
|
Au contraire. You see snow crackles all the time. They
just aren't very objectionable in an analog transmission
so long as they're not as continuous as a vacuum cleaner!
But ethernet _IS NOT_ analog.
| Quote: | current and in some situations, pulse dialing, typically
at 10 or 20 pps.
|
Even 20 pps has a "wavelength" of 10,000 km in TP cable.
There will be no harmonic reinforcement of interpulse noise.
Even rising edge and trailing edge are probably too far apart.
| Quote: | A pure sine wave has no harmonics.
|
http://en.wikipedia.org/wiki/Harmonic
| Quote: | Every other signal does. This means that everything on a
phone line is either a sine wave of the sum of a series of
sine waves. There is no other possibility.
|
This is one way (not the only way) to deconstruct signals.
But a perfectly square wave requires extremely high frequency
components at very significant power to sharpen the shoulder
and produce the very quick decay.
| Quote: | Once you have determined the various frequencies involved,
you can then determine:
a) the coupling of those signals between pairs and
b) any interfering effect of those signals on the desired signal.
Any other "conclusions" are simply nonsense.
|
A near-square wave can also be analysed analytically from
first-principles (Left Hand Rule & Maxwell's Equations). I'm
suggesting these are more appropriate than the simplifications
used for carrier-wave (your harmonics?) analysis.
-- Robert |
|
| Back to top |
|
|
James Knott
Guest
|
| Posted:
Thu Sep 08, 2005 1:11 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
|
|
Robert Redelmeier wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
If we're talking about dial pulses interfering with ethernet,
we're talking about harmonics.
Why only harmonics? There are other kinds of interference.
|
Such as??? Anything you can imagine, other than constant DC is composed of
sine waves at one or more frequencies. Any wave form, such as square wave
triangle wave, etc., are composed of sine waves at a fundement and harmonic
frequencies. Noise impluses consist of short duration sine waves
(sometimes called "damped" waves, in that they rapidly decay), no matter
what the pulse shape. "White" noise is simply a collection of sine waves
at many different frequencies. Can you tell me about anything, that can't
be shown to be composed of sine wave functions???
Here's something that might provide you with some idea of what's involved.
http://mathworld.wolfram.com/FourierSeries.html
| Quote: | Au contraire. You see snow crackles all the time. They
just aren't very objectionable in an analog transmission
so long as they're not as continuous as a vacuum cleaner!
But ethernet _IS NOT_ analog.
|
If you're referring to the snow on a TV screen, when there's no TV
reception, you are looking at noise from other sources, than electrical
appliances etc. However, this doesn't rule out the possibility of
interference to the TV at stages after the tuner. For example the universe
is filled with radio noise, from a variety of natural sources, including
the after effects of the big bang.
Also, while ethernet carries digital data, the signal is in fact analog, in
that a carrier is modulated by that data. 10 Mb ethernet uses Manchester
encoding and 100 Mb uses something called "multilevel threshold-3"
signalling, where there are multiple levels, depending on the data bits.
If you were to look at it with a scope, you'd see a complex analog
waveform. Also, if it wasn't an analog signal, that is some combination of
sinewaves, with equal enery above and below 0 volts, it couldn't pass
through the NIC transformers, without distortion. Incidentally, you can
take a simple modulation method, such as Manchester encoding and show that
it is composed of various sine waves.
I'm well aware of the harmonic structure of music instruments etc. However,
the fact remains that if you have a pure sine wave, it doesn't have
harmonics. Harmonics are only present, when you have a non-sinusoidal
waveform, such as square wave etc. If you can't accept that, then I
suggest you take some math courses.
| Quote: | Every other signal does. This means that everything on a
phone line is either a sine wave of the sum of a series of
sine waves. There is no other possibility.
This is one way (not the only way) to deconstruct signals.
But a perfectly square wave requires extremely high frequency
components at very significant power to sharpen the shoulder
and produce the very quick decay.
|
Where on earth did you hear that? Please read up on Fourier. He
demonstrated that *ALL* waveforms are composed of some series of sine
waves. That "perfectly square wave" is composed of a fundamental sine wave
and odd order harmonics, where the amplitude of each harmonic is inversely
proportional to it's order. Again, go back and take some math classes and
have your instructor explain it to you.
| Quote: | Every other signal does. This means that everything on a
phone line is either a sine wave of the sum of a series of
sine waves. There is no other possibility.
This is one way (not the only way) to deconstruct signals.
But a perfectly square wave requires extremely high frequency
components at very significant power to sharpen the shoulder
and produce the very quick decay.
|
As I recall Maxwell's equation and the (Flemming's) left hand rule, they
relate to the relationship between a moving magnetic field and induced
current. Other than that, what do they have to do with a waveform? |
|
| Back to top |
|
|
|
|
|
|
FAQ
Memberlist
Register
Profile
Log in to check your private messages
Log in