POTS and Ethernet over CAT-5 Cable

There is actually a lot of discussion about this in many engineering circles. The general consensus is yes, Ethernet uses two pairs, which leave two pairs left for another Ethernet circuit, POTS, audio, etc. The concern, from what I have read in blogs is if you were to add something to the two unused pairs that would create a high amount of energy (noise) that could bleed over onto the Ethernet pairs causing packet errors and retries slowing the link down, or even crashing it. A POTS line works fine except I have heard of the ringing cycle causing issues, but that was on a CAT5 and not CAT5-E cable.

Dan

You might take a look at the Ethernet spec, instead of just guessing; it specifically mentions using one (or both) of the spare pairs for POTS (or a second Ethernet). Why do you think they carefully avoided the 4-5 pair for Ethernet, when you can plug an RJ-11 right in there and use it for a telephone?

Isaac

Ethernet uses two PAIRS or 4 WIRES leaving 2 pair available for 2 POTS lines or another ethernet connection or some other low voltage application. In theory, using the other two pairs could interfere with the ethernet connection but I've had no problems where I've had to do it. The speeds you're running are probably less than the cable is capable of anyway so it's not a great concern in a residential application. If occassionally things slow down by a split second you'll never notice it anyway. As for breakout connectors, check

and other network hardware sources. It's probably easier to just change the wallplate to add the additional jacks and reterminate the wires.

From:BrianEWilliams sorry_no snipped-for-privacy@yahoo.com

Hello Brian,

There will be a serious current spike whenever the receiver is taken off hook or placed back. That may or may not cause packet losses on the data pairs. Ringing can also generate 90V or so and an open loop phone line can run up to such voltage levels as well. So if you accidentally miswire something ... bzzzt.

Utilities also have their rules and some may not endorse such wire mixing. Anyway, personally I wouldn't do it so I ran two CAT-5 to every location from the central closet. CAT-5 is cheap. Plus now it's future proof in case there comes a day when the other two pairs are being used for the data link.

You have to cut the cables anyway to connect an RJ45. In this case you'd just have to cut the sleeve back some more. But again, I wouldn't do it.

Regards, Joerg

The best advice!!!

Agreed. It's certainly not desireable but if a second cable isn't there or can't be readily added it will work. I know of no Utilities or even building codes that would have a say in this. The phone company certainly won't care nor will the electric, gas, water or cable companies.

From:Joerg snipped-for-privacy@removethispacbell.net

Hello Brian, I have done this exact same thing with my house. There are 6 double strands and 12 single of CAT-5 leading from my control closet to 18 RJ-45 wallplate jacks (single or double, or course). I can't remember where, but some ancient research I did led me to the discovery that an RJ-11 or RJ-14 (i.e. a single or double line POTS) plug will click right into the standard RJ-45 jack and tap the non-Ethernet conductors. I currently have only(?) 5 computers on the home network and may cut 1 or 2 laptops off for wireless. For the last 7 or 8 years, this has let me plug in a computer OR a phone at any jack and have no noticable interference to either. It was quite handy when my son would have 5-6 friends bring over their systems for a weekend of high intensity gaming warfare. Same reason I kept 10 lbs of hot dogs anf a case of Mountain Dew in the garage fridge at all times. I really wish I had been smart enough (and wealthy enough) to run dual coax to each jack at the same time! Isn't hindsight wonderful?

Good luck!!! Alan

"BrianEWilliams" wrote in message news: snipped-for-privacy@g14g2000cwa.googlegroups.com...

Here in the UK I run Ethernet and POTS down the same cat 5 and have never experienced any problems. Internal wiring for POTS uses three cores in this country. Ethernet uses two pairs everywhere. So that's only one POTS, not three.

I've wired it all without any special cutting open. I've terminated the fixed wiring at a wall plate which has one Ethernet socket and one phone socket. The patch cords are all normal.

If you don't want to modify your fixed wiring, a pair of "cat 5 cable economisers" will take you part of the way - they put two ethernet signals down one cat 5 cable. Then you'd need two ethernet-to-POTS wiring adapters, if such things exist.

Thanks for all the very helpful replies!!

I should have mentioned that I am in the US, so POTS takes two wires. My assumption that Ethernet takes two wires was wrong, but that still leaves room for two POTS lines on the remaining 4 wires.

I need to reread this thread a few times to really understand what I need to do, but one question comes to mind.

If turn the ringer off on the phone connected to the CAT-5 cable, will that help solve some of the issues with the ring voltage possibly causing packet loss?

Bruce,

Thanks for the extra info. I just got the phone up and running on the brown/white pins 7/8 twisted pair. This website was a big help:

as was the advice posted here. Thanks to all.

FYI, I just sliced open the CAT-5 cables and spliced in the phone line.

Brian

In a shared cable, you should only carry a pair for the POTS wiring, pins 2 and 5, and use PABX master sockets to recreate the bell wire (pin 3) at the far end. If you carry all 3 wires, the twisted pairs can't work correctly to minimise noise and cross-talk.

Hi Issac:

I thought I was making a "responsible" answer. No where have I been able to find a EIA/TIA, IEEE, etc. spec/standard that states that using CAT5 cable for simultaneous applications that include ethernet is "approved". If I am missing one, please send it to me as I would like to read it so I am better informed when I answer questions. That said, I stand behind what I posted. The general consensus is to make a informed decision, but most articles I have read say do not do it. Some reasons given are: 1000mps use, PoE uses, etc. Can it be done, yes. Would I do it, no. Two sites that talk about it:

Regards Dan

No need to turn off the ringing. The ringing voltage isn't going to cause any problems. The use of POTS with ethernet is per specification and won't be a problem. Where I haven't been able to readily run another cable I have done this a number of times with NO problems ever. The pairs you have available for phones are the blue/white and brown/white pairs. The blue/white pair appears on pins 4 & 5, the two center pins of the RJ45 jack so you could just plug th phone in and it will work. If you plug an RJ45 splitter in then you can plug a phone in one side and an ethernet cable in the other. To use the brown/white pair, which are on pins 7 & 8, will involve a bit of custom configuration of the phone cord.

From:BrianEWilliams sorry_no snipped-for-privacy@yahoo.com

Hi Alan,

I ran single CAT-5 and single coax to each room in my house as it was being built, each line terminating in a patch panel in the basement. Then the cable TV comes in over its own coax network to each room. I've had lots of fun with this setup, but I definitely made some mistakes with the placement of the wall jacks that are obvious in hindsight.

Now that I can run POTS over the CAT-5, I've stopped wishing I had run dual CAT-5. I think that with some tinkering around, I can run two video streams on my single coax, but I'd have to dig up the old posts that led me to this conclusion. Just don't have the need now, but my boys are young, so time will tell.

Enjoyed your post, and it makes me imagine the mayhem in 10 years. They are so small and cute now that it's hard to believe they will be full-sized before I know it.

Brian

You can make your own box easily enough. White/Blue for phone. Wh/Gr and Wh/Or for Ethernet. Wh/Br not connected. It won't run gigabit.

It is fine for household use. For the limited amount I have used it, I get no CRC errors with the phone ringing, or at all, for that matter.

Also don't forget that modern enterprise wireless access points are actually powered off spare wires in the ethernet cable these days.

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