11

I have been researching this for some time now and feel that I am almost ready to begin. I have run into a slight problem though that I can't seem to find any answers for. The telephone cables in my house are all connected to one single cable and they branch off from each other at each telephone jack. If I make the ethernet connection at the central cable will this run ethernet to every telephone jack in my home? Assuming I retrofit the correct connections on the ends of course. Every video tutorial I've seen on this have several phone lines running from the box to their respected telephone jack, which would make this much easier.

5
  • 2
    What kind of cable (type and number of wires) and what is your internet source. May 10 at 18:47
  • 7
    you cannot use phone lines for ethernet
    – jsotola
    May 10 at 19:32
  • 2
    Post a photo showing the colours of the wires within the cable, it'll help us identify the type of cable that's presently there May 11 at 6:40
  • 1
    This is slightly off-topic, but you may be able to get a more reliable connection with ethernet over power-lines. You would need an adapter at each end, but that may be cheaper and easier than rewiring the house.
    – Rich Moss
    May 13 at 0:12
  • 2
    @jsotola Yes you can, it will just be slower than modern ethernet.
    – JBentley
    May 13 at 13:01
36

Nope! Plain Old Telephone Service (POTS) jacks were usually daisy chained as you describe. Ethernet requires a "home run" from each jack to a modem, router or switch. Also, it's probably cat-3 which is unsuitable for Ethernet.

EDIT: Based on comments (which sometimes go away, but answers don't), I'm adding to my answer here: According to others Cat-3 can be used for limited ethernet service (I wouldn't recommend it), but every jack would have to be wired in a home run configuration, which is uncommon for POTS wiring. Next: As others commented, the POTS wiring might not even be Cat-3, it could be 4 wire cable (Red, Green, Yellow, Black) which was very commonly used back in the day, which wouldn't work at all.

9
  • 13
    Plenty of old telephone cable is not even Cat 3. May 10 at 17:10
  • 2
    @manassehkatz-Moving2Codidact Yep, you're right about that: Red, Green, Yellow, Black! May 10 at 23:29
  • 16
    Actually CAT3 is UTP wire and is suitable for networks including Ethernet up to 10M bps. In practice it can even handle 100M bps for relatively short runs although that is in no way recommended. I would not ever install CAT3 today but using it for a existing run can be done. Taps? No way!
    – jwh20
    May 11 at 1:20
  • 4
    Thank you for this comment and all comments on this have been very helpful. I do know that it is a cat-5e cable but since it’s daisy chained throughout the house I won’t be chasing this any further. My next step is to run a lan cable up to the attic and drop the cable down the wall to an opening there where I can rig a connector to it.
    – Zards
    May 11 at 19:37
  • 4
    If one wanted a Rube Goldberg solution, they could always use Appletalk on the POTS line and connect every phone port to its device through an Appletalk-to-Ethernet adapter. Of course, there's reasons why Ethernet was adopted over Appletalk.... :-) May 11 at 20:10
20

There is a separate issue of the type of cable. Telephone can run on CAT 3 (10 Meg. ethernet), CAT 5 (100 Meg. ethernet), CAT 5e (1 Gig. ethernet) but also on much older types of cables that are not suitable for ethernet at all. Assuming that the cable you already have in place is at least Cat 5 (100 Meg., which is arguably enough for typical internet usage), the topology is the next challenge.

Standard analog telephone service (POTS) could have many devices - telephones, answering machines, fax machines, modems, etc. - on a single line. All devices are connected together with a pair of wires. The polarity of the wires usually doesn't matter, and the devices could be wired in a star topology (a bunch of cables joined together at one end with a device on each cable on the other end) or chained one device (or more commonly, wall jack for a device to plug in) to the next. A single chain through a building is generally cheaper to install (less wire, a lot less labor if installed while the walls are open during construction) than a star configuration, so until home networks became common, that was the standard installation method. (Exception: the house I grew up in actually had separate runs to each room, though that was in the days before twisted pair ethernet, so it didn't matter much).

Originally, ethernet used coaxial cables with a tap into the cable for each computer. This was replaced many, many years ago, by twisted pair cables using hubs and switches. With twisted pair cabling (as used for ethernet, there are other varieties for other systems that are not applicable here) with each cable providing a single point-to-point connection, generally between a computer and a hub or a switch. (Almost all ethernet networks now use switches, not hubs, but that doesn't actually matter much for this discussion.) There are also point-to-point connections between switches, between switches and routers, etc. A typical magic internet box WiFi router is actually 3 devices in one: Router, WiFi access point and ethernet switch.

The end result is that daisy-chain telephone wiring is extremely common but also nearly useless for ethernet networking. The exceptions are:

  • If the cables are high-enough quality (at least Cat 5) then you can often get one good connection per chain.
  • Even if the cables are below modern ethernet quality, you may be able to use some sort of network extender to get a good signal to one location.
  • If the cables are loose then you may be able to use the old cables to help pull new cables.
7
  • 1
    "Originally, ethernet used coaxial cables with a tap ..." and that topology is where ethernet gots its name from and the need for collision sensing. Ironically the older versions would be actually suitable for a passive tapped or chained POTS topology.
    – P2000
    May 10 at 19:28
  • 2
    Also, ironically, given that ethernet got it's start on thick coax, then thin coax, later evolved to twisted pair. TV coax was commonly installed and needed home runs, and now with all the "cord cutting" going on TV coax wasn't being used, but and here's the irony, MoCA technology supports re-purposing old TV COAX for ethernet...guess it's "Back to the Future". May 10 at 23:28
  • 4
    My "magic internet box" is also a fiber endpoint, a DSL modem (unused), and a VOIP adapter. I think it can also function as a file/media/print server.
    – Jonathan
    May 11 at 15:24
  • 1
    @Jonathan Odd combination to have DSL (older and/or low-end) combined with fiber and VOIP. Not odd to have that combination of functions somewhere, but odd to have it all in one box. May 11 at 15:26
  • 3
    @manassehkatz-Moving2Codidact: Well, it does. I guess that's so the ISP only has to stock a single type of end-user equipment.
    – Jonathan
    May 11 at 15:33
7

If it's a reasonably modern twisted pair telephone cable, then it's equivalent to CAT3 Ethernet. For Ethernet, that's obsolete by today's standards. It's only good for 10Mbps, or maybe 100Mbps over short runs.

By comparison, all the cables you can buy today are CAT5e (100Mbps to 1Gbps) or CAT6 (up to 10Gbps).

What this means is that your Ethernet connections may be slow by modern standards, or unreliable.

Older telephone cables that are not made up of twisted pairs are unlikely to work at all.

5
  • 6
    Plenty of old telephone cable is not even Cat 3. May 10 at 17:08
  • @manassehkatz-Moving2Codidact True. I was assuming reasonably modern twisted pair cable.
    – Simon B
    May 10 at 17:12
  • 2
    Age of house not specified. If > 35 years-old then (unless upgraded) definitely not modern twisted pair cable. Quick search: USA mean house age = 37 years. May 10 at 17:17
  • Cat 5e can run gigabit ethernet over the full 100 m. (Cat 6 and 10GE has the lower distance limitation, 55 m or something like that)
    – ilkkachu
    May 11 at 14:13
  • There's still plenty of Cat5 Ethernet cable (up to 100 Mb/s) running around, not just Cat5e/6.
    – Vikki
    May 12 at 0:56
5

You can't do that. Modern ethernet requires point to point connections, not bus topology. And it is quite likely that since your telephone was wired bus topology that the wire quality is inadequate to even try using the phone cable for even a single computer connection.

Edit: Really for a 100% accurate answer to your options we need to know What kind of phone cable (type and number of wires) and what is your internet source. There are some extremely rare situations where some answers might miss some narrow options. Like if your source is DSL, you could make internet available at any jack, but you could only connect one jack at a time to a computer. Or if internet from a coax you may be able to place a router at one location that has multiple taps and make ethernet available at multiple locations, but not through any downstream taps.

8
  • 1
    Not quite "point to point" rather a "star" wiring pattern better describes the topology. Every jack needs a home run to the router/modem/switch. May 10 at 17:04
  • 1
    @GeorgeAnderson Wouldn't any hub in a star be considered a node, any connection from node to node be point to point? May 10 at 17:11
  • 2
    Point to point is a more accurate description of the topology. In that, there is a dedicated cable from an ethernet jack of the switch/router/hub to a computer or other device. A star would technically be coming out of one ethernet port of a switch/router/hub and go to multiple devices, with a separate cable to each device. Subtle differences.
    – SteveSh
    May 10 at 19:57
  • 1
    @NoSparksPlease Also, if you have a home run, it doesn't mean that can't be shared among devices. Simply use an un-managed switch locally (like in a home office) to plug in your devices and connect to the home run to the modem or router. They are very inexpensive, no setup needed, about as complicated as a triple tap plug for a 120 volt circuit! LOL May 10 at 23:19
  • 2
    If you have a job that requires wired connections then you really just need to pay to get it right. Trying to implement any legacy technology and equipment will likely not be supported by the employer terms, and will leave you disappointed compared to just a retail wireless 802.11n or 802.11ac router and wireless cards in your desktop computer. May 13 at 20:06
5

If I can weigh in here. I have only used cat5 and up in my professional life, but we did do some hacks in a pinch.

If you give more info (why you do it this way, photos of cables etc) I could be more help.

If the cabling was done in a star configuration (all connected to a central point) then you are at least lucky in that regard.

Firstly lets start with the cable type. Ethernet cable is twisted in a way that minimizes electromagnetic interference. Depending on the type of cable installed in your place you may get away with using 4 wires per connection. This would mean connecting your RJ45 connectors pin 1,2,3 and 6 matching on each side .If you have 8 wires (4 pairs) then just match both sides. You can also make a direct connection between 2 network nodes (pc's, pc to printer etc) by connecting 1 to 3, 2 to 6, 3 to 1, 2 to 6. This is called a cross over cable. I once had to run 2 seperate connections over 1 cat5e this way just to get a temp net up and running(don't ask).

Sadly this will give you at best a pathetic 10mbps. To make this into an actual (terrible) network you would need to install a network switch at the central point and connect your newly crimped connectors.

Best option if you plan to remove/repurpose the telephone wiring in your place (check if legal!) , just buy(or salvage / ask at sites where buildings are decommissioned or wiring replace ) some cat5e or cat6(better) and use the old telephone wires to pull the new cables through. Use proper connectors and a switch( ask around if no budget) and you will be good to go. Your future self will thank you.

Still if you are just doing this to see if it works, great! Messing with stuff is how we learn.

4
  • 1
    Make sure the attachment is very secure if you decide to pull a new cable through. Test that how it would respond to moderate amount of force. If the cables detach in the middle of the pull, you won't get a 2nd chance. May 11 at 23:05
  • @DmitryRubanovich excellent point. That could be a question all by itself - "how to tie a cable to a draw-wire so that it doesn't slip off while pulling cable through walls"
    – Criggie
    May 12 at 12:39
  • 1
    @DmitryRubanovich yes absolutely. I have lost a pull or 2 that way, then had to grab the fish tape, feed it through and pull again. May 13 at 6:45
  • @DmitryRubanovich yes absolutely. I have lost a pull or 2 that way, then had to grab the fish tape, feed it through and pull again. The most effective way I have found was to take the wire from the core of the new wire and the installed wire and bend each set into a hook, think > . then hook the 2 sides into each other and twist to secure. Then I would take insulation tape and wind around this setup taking care to keep the join as streamlined as possible. Bulky joins usually get stuck. This way takes about 2 minutes to do but it beats the time of re doing a botched pull! May 13 at 6:51
2

Can you run Ethernet over an old phone cable? Not officially, but possibly in practice.

You can run 10BASE-T and 100BASE-TX Ethernet over any two wire pairs (the other two wire pairs in a standard "RJ45"/8P8C Ethernet connector are unused until you get to Gigabit Ethernet).

The standard requires twisted pair cables (to reduce interference), which most older phone cables are not, but for short runs (say, less than 20 meters), you may be able to get away with it. It depends on both the cable quality and endpoint hardware.

Can you connect three or more Ethernet devices to the same physical wire (daisy-chain/bus)? With ancient (1980s) coax Ethernet, yes, but not with modern "RJ45" form-factor Ethernet. Connecting just two devices and leaving the other phone sockets unconnected might work, though the unused sockets do add interference.

TL;DR: It may be feasible to connect two devices, but you won't know before you try.

If you want wired Ethernet without dragging new cables, you're probably better off looking at an Ethernet-over-powerline solution like HomePlug.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.