Single Cat5e for Computer Network & Telephone?

What a relief! Thank you.

Yep, no problem. I have my cat5e running with 1 network and 2 phone lines, utilizing all 4 pair in one cable.

Yes you can, except for gigabit.

In very many cases this works well but it is not a recommended practice.

MIst commonly used networkign technologies use only to pairs. Examples of such technologies are 10Base-T and 100Base-TX Ethernet.

But keep in mind that there are also other ntworkign technologies that can use different pairs and even need all pairs (for example 1 Gbit/s Ethernet needs all four pairs).

I think this would work without problems if the line you have comes form the local PBX device. Most propably things work for most time even from directly outgoing line with the same cable, but I would be a little worried about situation when lightning strikes nearby which can cause overvoltage on telephone line.. consider overvoltage protection on the place where telephone line enters the building.

Twisted pair ethernet was designed to share existing telephone cables.

Given the great difference in frequencies involved. There's unlikely to be much interference, between an analog voice line and ethernet. Most of the voice energy is below 3 KHz. Ethernet signaling is well above that.

Yes. But 10baseT, not 100baseTX (which still usually works).

-- Robert

Granted. But the _design_ was for POTS & 10baseT shared-sheath.

-- Robert

Actually, it's usually 20 Hz. However, that's even further from ethernet frequencies than voice. That 20 Hz signal has to couple into the data pairs and then somehow make it through a transformer, that designed to pass much higher frequencies. Also, it's the current, not voltage that determines induction. So, the 20 Hz ringing current, has to couple from one twisted pair to the next, which will result in common mode interference, at 20 Hz. The transformer is designed to couple differential mode signals, not common mode, to the NIC. The transformer is designed to pass signals in the MHz range, not 20 Hz, and there's also additional filtering in the NIC circuit. It's unlikely you'll find any interference from ringing.

And how does 100baseT differ, that it would be more sensitive? It works at higher frequencies than 10baseT.

You are right that most of the voice below 3 kHz and the signal level is quite low. And Ethernet main energy in 10Base-T is somewhere at

5-20 MHz range. The most problematic I quess could be the ring signal, that is typically around 90V AC 25 Hz. Generally you can expect very good network performance with propably very temporary problems (possible on telephone ring, on/off-hook, pulse dialling etc. if the cable is not very good). 10Base-T is very robust and practically works well with even where same cables are shared with Ethernet and telephone signals. There are even products that run 10Base-T Ethernet and telephone signals on the physically same wires inside the cable (there are several companies that make such special adapter products). 100Base-TX runs at much higher rate and uses more compplicated coding system that is more sensitive to the noise errors.

I have done soma laboratory expriments related to both of those Ethernet systems. With a sutiable filters I could successfully run both 10Base-T Ethernet signals and telephone signals on the same wire pair. I posted some news articles related to this aroudn on eyear ago to one Finnish newsgroup... Doing that with 100Base-TX did not work that well...

100baseT signaling is at 125 Mbaud. You'd have to generate some incredible harmonic levels to get interference at 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 harmonic of the pulse dialing at 10 Hz, you'd have at most 1/10 the voltage at 100 Hz. At 1 Khz, only 1/100th etc. Now extend that up to the MHz range and you'll find you likely can't even measure the harmonic amplitude. Also, power is proportional to the square of the voltage, so if the amplitude is 1/100th, then the power is 1/10,000th. You'll soon find that the harmonic levels are far below the desired signal level. This is even assuming you've got a direct electrical connection. However, when you're sharing a cable, you don't have 100% coupling, between pairs, so the interfering signal will be considerably lower still.

In short, you'd have a tough time showing that any signal, normally present on a phone line, is capable of causing any interference to the ethernet signal. If an ethernet transceiver can deal with near end cross talk, from it's own tranmitted signal, it can more than handle any possible interference from a phone line.

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.

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.

"frequency" may be a useful concept for broadband or carrier-wave signalling, but neither of these ethernets is.

The signal plateaux are 1/10th as long for 100baseTX, therefore more prone to being affected by transients. Ringing current is unlikely to be a problem because although it is high, it is continuous and smooth AC. Going on/off hook (or pulse dialing) might be, especially if there isn't parasitic capacitancy or deliberate contact capacitors to round the shoulders. You also have to cope with "bounce" from mechanical contacts.

Of course, ethernet is extremely robust, and higher level TCP/IP protocols can deal with errors remarkably well. So it still appears to work, just like the many installations with split-pairs.

-- Robert

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.

I lose ports occasionally, and I'm not entirely sure what fried them, even though I don't have any outdoor wire.

Because both cable and phone service entrances have grounded protection.

Of course. The CN Tower certainly has carefully, custom designed lightening protection. Proper grounding and caging for equipment areas.

-- Robert

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.

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.

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

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.

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.