Networking Oppos

"IJustWantMyZBack" (IJustWantMyZBack) 09/28/2020 at 13:26 • Filed to: None

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I was hoping to wire up an ethernet port here and it looks like standard cat5 wire to me. But I don’t understand the split RJ45 wiring. Is this for a t elephone/DSL connection? I don’t remember this from my networking class.

VW Nardo for your time.

Shane Moore > IJustWantMyZBack 09/28/2020 at 13:56

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I’ve never seen that before. To me it looks like somebody using one cable for two connections instead of running two cables . I can only imagine you run into some crazy cross-talk with that setup.

My X-type is too a real Jaguar > IJustWantMyZBack 09/28/2020 at 13:58

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Yes anything built or wired mid 90s to mid 2000s would have wired phones with cat 5, this allowed 4 lines per run. There should be either a phone company punch down block or one outlet with the terminals going to the outside world. 

jminer > IJustWantMyZBack 09/28/2020 at 13:59

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What was plugged into those jacks?

It could have been just they were used as RJ11 phone jacks, of for some reason pushing either just data or just power down them.

Tripper > IJustWantMyZBack 09/28/2020 at 13:59

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Hard to say what that was used for, probably phones but you can clip those and wire up a single cat 5 e jack. do the same at the other end and you should be good to go.

PyroHoltz f@h Oppo 261120 > IJustWantMyZBack 09/28/2020 at 14:15

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Is this an office or home?

Many residential wiring for phone (rj11) was done with cat5 but rj11 won’t connect to an rj45 port. My guess is this could have been a 10 BaseT setup instead of 100 /1000, I believe you only need 2 pairs for those and a single cable run will give you two different connections.

A modern way to solve this problem is to put a switch at either end of a single cat5e run, to get multiple computers talking over the ‘ trunk’ line.

Just wire this up as a standard cat5e on both ends.

BoxerFanatic, troublesome iconoclast. > IJustWantMyZBack 09/28/2020 at 14:23

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It looks like they were trying to use one cable for two ethernet lines, rather than running another cable.

Without Gigabit Ethernet, or Power-over-Ethernet, pins 4, 5, 7 , and 8 are reserved/unused.

Pins 1, 2, 3, and 6 (orange-white, orange, and green-white, green pairs) are used for transmit and receive.

It looks like they repurposed the blue and brown pairs onto the 2nd RJ45 punch-down in the transmit and receive pins.

That can work, but it is not ideal. The twist rates on the various pairs are not the same, especially on Cat5e, 6, 6a, and 7... and just using the reserved pairs for another line is not ideal. It may work, but it isn’t likely to work well, and it is obviously not standard to come back and support afterward.

The blue pairs technically can be used to inject a single-line phone into an RJ45 and an RJ11 jack may touch just those two center pins, 4 and 5, while the ethernet would work around that. That is also not ideal, compared to running a dedicated telephone station wire.

Pins 4, 5, 7 and 8 are also sometimes used for parallel transmit-receive to double bandwidth for Gigabit Ethernet over twisted-pair, and are otherwise reserved for 24, 48, or 56vdc low-amp power over ethernet.

Socketing a POE device into either end of that cable, especially a POE source, could either just not work, or if only one end were re-terminated properly for T658B , could cause some sparks on the other end, or at least burn out the end-point device’s ethernet port.

IJustWantMyZBack > PyroHoltz f@h Oppo 261120 09/28/2020 at 14:27

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This is in a home. Sounds like I need to confirm the end point and rewire the port. Thanks!

IJustWantMyZBack > jminer 09/28/2020 at 14:28

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When I moved in nothing was plugged in, the ends were stuffed in the box and only the coax was sticking thru. Sounds  like I need to confirm the end point and rewire the port.

MUSASHI66 > IJustWantMyZBack 09/28/2020 at 14:35

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I had that in my house - we had 2 phone jacks all over. I swapped them all to a single ethernet jack, and did some creative wiring in the basement to make my house wired for ethernet which I used instead for landline which I didn’t use. 

BoxerFanatic, troublesome iconoclast. > BoxerFanatic, troublesome iconoclast. 09/28/2020 at 14:37

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Instead of non-standard wiring... 5 port ethernet switches are very inexpensive, and can multiply one ethernet line to multiple ethernet ports, and let the traffic management happen in OSI layer 2, rather than physical layer 1.

facw > IJustWantMyZBack 09/28/2020 at 14:46

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Yeah, looks like some non-standard doubling up. Honestly if it’s only cat 5, I wouldn’t even bother with it at this point, wifi or powerline adapters will probably be faster anyway. If you want the hardwire, you should pull new cable.  

Moltenburn > IJustWantMyZBack 09/28/2020 at 15:53

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Sounds like you got this already but check port on both ends and rewire. Not sure why they went that route versus just running a switch

liam > PyroHoltz f@h Oppo 261120 09/28/2020 at 15:56

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RJ11 will connect to an RJ45 port, but it will only use the middle four connectors.  It was designed to enable that use - this is a good page on it  https://tombuildsstuff.blogspot.com/2015/01/rj11-phone-to-rj45-jack.html

PyroHoltz f@h Oppo 261120 > liam 09/28/2020 at 16:54

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Good link, thanks.

RJ11/12 plugs will fit directly inside an RJ45 jack. It’s not preferred since you might damage the other pins but it is designed to work that way.

That last part is what I was always concerned with but I suppose it doesn't really matter if the jack is only wired for the 4 pins.

MiniGTI - now with XJ6 > IJustWantMyZBack 09/28/2020 at 17:33

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Yeah as others have said , I think someone was trying to send 2 lines over one cable, which you can do with 100 megabit as only 2 pairs are used. If you want to do gigabit speeds require with normal pinout to a single connector. You’ll probably find 2 plugs at the other end.

I think the college dorms were wired that way when I was there in the late 90s, before WiFi. 

Jake - Has Bad Luck So You Don't Have To > IJustWantMyZBack 09/29/2020 at 09:15

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I’ve seen this a lot. It’s standard operating procedure in the mid 2000s to get two 100BASE-TX connections out of one cable run. Hotels would frequently split off 5 and 8 to get an analog telephone line alongside an ethernet port.

Marcel > IJustWantMyZBack 09/29/2020 at 09:24

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Looks like 2 Ethernet ports on one cable. 10/100 without POE only uses 4 wires. This person needed an extra port but didn’t want to run a second wire, so he used the other 4 unused wires that are usually used for POE applications.  GBE needs all 8 wires.