10base-T & POTS in same Cat-5 cable?

How long ago is "many years", relative to the introduction of

10baseT?

Rich did *not* make any such opposite claim.

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.

Who said anything about harmonics?

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.

It doesn't have to be. Frequency is *not* what determines whether it will interfere or not.

Please cite the specs for a form of ethernet where the receiver can handle +/- 300 volt burst of random noise hits.

"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.

[snip]

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

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

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?

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.

Yes.

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.

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.

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). 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.

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.

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

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.

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.

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.

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???

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.

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

10baseT was early 90's. I don't have a date handy for cat 3, but cat 6 & 7 were being planned in 1997.

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.

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.

If the ethernet circuits are design to operate in the 5 - 10 MHz range, there won't be much effect from < 4 KHz.

"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.

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.

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.

From where I sit, it looks like you disagree. See the above quotes.

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.

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) _______________________________________________ _______________________________________________

Try 1991 for CAT3.

You didn't buy it in 1989. (CAT1 is a classification that appeared in

1985 though... :-)

Can you actually read. "designed for telephone lines, but I don't think 10basetT was." *Telephone lines*.

CAT3 is data network cable. CAT1 is "telephone lines".

Looks more like you just don't have a decent set of facts to go on, and perhaps have a reading disability.

Yes, the point is they did *not* recommend CAT3 in the 1980's.

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.

Actually, it is up to 120 V RMS. Which is 297 V P-P.

Typicical ring generators actually produce 90 to 105 V RMS.

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.)

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.

See above... same effects, same differences.

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.

Ring voltage is commonly 90-105 *RMS*. It is allowed to be as high as 120 VAC RMS.

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.

Which is the reason it uses twisted pair, which provides high common mode rejection of induced noise.

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.

Where'd the 120V come from? Phone ring generators are nominally 90V, as you then say in the last line.