I don’t know much about cabling and need some help identifying what this is.

There this port that has a phone and a computer icon near where the fibre/coax entries are.

And in one of my room there’s this dual port jack with those cables : enter image description here enter image description here enter image description here


3 Answers 3


No, but what you have might be usable.

The jacks, at least the ones where you show the back with the screw terminals, but probably the other ones as well, are standard 4-wire phone jacks, which can handle one or two ordinary phone lines (POTS) or many (but not all) traditional phone systems, except for VOIP. VOIP uses regular Ethernet networks, which is what you want but don't have.

My hunch is the computer symbol dates back to old modem days. In ye olden times, computers in a typical home or small business were not networked but many would have a modem connected to an ordinary phone line to call up an internet service provider or, in even older times, Compuserve, AOL, bulletin board systems or proprietary systems such as minicomputers or mainframes for shared databases or accounting systems.

The possible good news is that these are 4-pair cables, which are what you need for Ethernet. The likely bad news is that they are probably Category 3 (Cat 3) cables. Cat 3 is only rated for, and reliable at, 10 Mbps, which is marginal for modern networks, video on the internet, etc. Zoom and similar platforms typically specify 3 Mbps - 4 Mbps for a single video user. 10 Mbps in theory should be enough for 2 simultaneous users or 1 plus miscellaneous email, web browsing, etc. However, I have seen compatibility issues with newer switches and equipment with older 10 Mbps networks. In theory most equipment is backwards compatible. But reality is not always the same as theory.

Cat 5 can handle up to 100 Mbps, which is good enough for typical uses. Cat 5e can handle up to 1 Gbps (1,000 Mbps) and has been standard for many years. If the cables are Cat 3 then don't even try to use them for modern (100 Mbps and up) Ethernet. If the cables are Cat 5e or above then you're all set (maybe...see below) and if they are Cat 5 then they probably are usable for things that don't really need more than 100 Mbps - e.g., OK for a computer or two web browsing, Zoom, etc. but not for an in-house network with serious data transfer needs.

If the cables are not good enough, you may be able to use the old cables to help pull new cables through the walls. That depends on whether the old cables are stapled or otherwise secured in place, which is likely if the old cables were installed before the walls were finished but unlikely if the old cables were themselves an addition to an already existing building.

Adding Ethernet jacks to existing cables is a relatively simple process. There are special tools required to do it "right", but they are not expensive and not hard to learn to use.

But there is one more possible problem: topology

Traditional phone lines, including fax and modem lines, could be daisy-chained from one location to the next. Ethernet doesn't work that way. Well, usually it doesn't - within certain constraints you could use Ethernet switches as a way to bridge pairs of cables. But generally speaking Ethernet is wired in a star topology - lots of cables that start at one location (which is where you place a nice big switch, and possibly your router, though not necessarily) with each one going to a jack in a different room. Your pictures show a typical daisy-chained configuration. So even if the cables are Cat 5 or above, you can likely, practically speaking, only connect one location as a regular Ethernet connection, without quite a bit of extra equipment.

  • 11
    the computer symbol is for connecting an XDSL modem
    – Jasen
    Dec 14, 2022 at 1:07
  • 1
    @Jasen The first box (surface mount) looks to me like a probably 2-pair phone cable splitting to two jacks. The wall plate with 2 jacks looks like Cat 3 (possibly Cat 5) cables with only one pair from each cable in use. To me, that looks like voice line + modem line in one place and just voice line in the other. I have seen (and installed) quite a few different DSL filters and DSL filters/splitters, but that first box looks to me more like just a double jack, and the wall plate clearly (to me) has nothing to do with DSL. Could there be DSL on one of these instead of plain modem? Possible. Dec 14, 2022 at 1:43
  • 2
    Plain Jane 2 port surface mount. Probably a round 4-wire phone cable in red/green-yellow/black, but as evidenced by the picture of the back of the wall-plate, only using one of those 2 pairs. Not a DSL filter or splitter at all, that's a conclusion jumped way too far.
    – Ecnerwal
    Dec 14, 2022 at 3:14
  • 1
    Likewise, the claim that the computer one is wider is, in both cases, not in the picture, just in the place you jumped to so you're seeing things that are not there. They are exactly the same. 6 position 4 contact bog standard Ma Bell RJ11 phone jacks.
    – Ecnerwal
    Dec 14, 2022 at 3:47
  • 1
    It's a myth that you need Cat 5e or better for gigabit; the 1000BASE-T protocol was specifically designed to work within the limitations of Cat 5, because at the time that's what almost all of the installed base was. But the cable in pictures 2-5 isn't nearly twisty enough to be Cat 5 -- it's Cat 3 at best. Dec 14, 2022 at 18:45

The top one is a DSL splitter

Digital Subscriber Line/Loop (DSL) is a way to get internet off plain old telephone service. Also known as ADSL, ADSL2, VDSL, VDSL2, etc.

The sound of the DSL traffic would be very screechy to the telephone user, so the filter was put on the "phone" side to remove all the high frequency DSL signals. Every phone needs such a splitter or filter.

It is not ethernet, however the cables in the wall look reasonably modern, like Cat3 or Cat5, might be reusable by putting Ethernet faceplates here. Ethernet speed would likely be limited depending on wire performance. A lot of that old stuff exceeds its spec enough you can still get workable speed out of it.

Ethernet isn't designed to be wired in daisy-chain style, but it can be by over-using hubs and switches. The topology might force you to put a hub or switch at every outlet. But I don't gather you plan to use more than 3 of them, so that won't be so bad. Note that 10Mbit and 100Mbit ethernet only require 2 pair (4 wires). Thus on common 4-pair cables, you can actually squeeze two separate Ethernet routes (out and back).

The second one is just a 2-socket cover plate. Nothing special going on there.

  • 3
    Those terminals having nothing to do with DSL. Sure, one use would be to connect a filtered line to the unlabeled jack and an unfiltered line to the computer jack, but it could just as easily have been meant for two separate phone lines, one for voice calls and the other for a regular dial-up modem.
    – chepner
    Dec 14, 2022 at 13:46
  • 1
    @chepner good catch, yeah, the "DSL splitter" only applies to the top photo. Dec 14, 2022 at 19:52
  • 1
    I'm not convinced it has to be a DSL splitter. It, too, could simply provide two phone jacks, with a suggestion that one line is for a modem and the other a regular phone. (It could, for example, take a single RGYB line and connect the RG to one jack and YB to the other). (I don't know what's going on with the wiring on the third picture; it looks like both halves of a single twisted pair is connected to the same terminal.)
    – chepner
    Dec 14, 2022 at 20:02
  • 1
    locally, DSL splitters came in two varieties. Multiple plug-in filter that were needed at each analogue telephone and the DSL modem could go without one because it ignored voice frequencies, OR a single potted block that did the same job of filtering out DSL noises that was upstream of the voice ports but downstream of the dedicated modem port. OP's labelled port might have such a hardwired filter upstream somewhere in the home.
    – Criggie
    Dec 14, 2022 at 20:02
  • 1
    @criggie that first one is a DSL filter. I was mistaken about the wall plate, but what you mention may apply to that. Putting the filtered line on the one marked for voice, and the other line on the unfiltered raw signal. Dec 14, 2022 at 20:42

Not likely.

The wiring in your last 3 pictures is likely Cat5, being used as telephone wire (one pair in use) and the fact that two wires are seen here means they daisy-chain from port to port (as opposed to home-runs which are necessary for network cabling).

Additionally, none of the ports look wide enough to be RJ-45 (the network standard with 8 pins) these are probably RJ-11 (telephone standard with 2, 4, or 6 pins). The back of the plate has 4 contacts, only 2 of which are in use.

If you're not using landline telephone you can see about using these cables to pull real network cable (Cat5e or Cat6 are the most popular) into these locations and replace the wall plate with a real RJ45 network jack to use for computer networking. As-is, you probably won't get much mileage at all out of them.

  • My system still uses a filter between the phone line and modem/router to prevent noise. It plugs into the phone jack then the phone and modem plugs into the filter. This seems to combine the filter into the phone jack.
    – crip659
    Dec 13, 2022 at 23:07
  • 3
    No, it doesn't. That's a surface mount 2-port jack in the first picture, and you can certainly see the lack of any filter, and the single phone line on the back of the 2-port wall-plate. This is simply one phone line with two ports and no filters in evidence, from the days of 1200 to 56Kbps dialup modems. Nothing more. Ain't a thing looking DSL here.
    – Ecnerwal
    Dec 14, 2022 at 3:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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