When [googling “ethernet splitter”](https://www.google.com/search?q=ethernet+splitter&tbm=isch) intuition immediately tells that you can have one input (where the cable coming from the router enters) which can be split to 2 computers at the other end.
However, this is not how it works:
>To use splitters, you’ll need two: one to connect your two devices, and another at the other end to “unsplit” the connection. This means you’ll still be using the same number of Ethernet ports on your router as if you were using two separate cables. You don’t add any Ethernet ports by using a splitter, you simply share a single cable.
(source [https://www.howtogeek.com/797864/ethernet-splitter-vs.-switch-whats-the-difference/](https://www.howtogeek.com/797864/ethernet-splitter-vs.-switch-whats-the-difference/))
**QUESTION**: why isn’t the signal simply **split** ? What is it that a switch does differently ?
In: 1
Are you old enough to remember party lines, or have you at least heard of them?
Back when the telephone system was being rolled out, some communities that were too remote or small to pay for dedicated phone lines for every household instead got a “party line”. It was basically a single phone line that everyone in the neighborhood had to share. Anyone could pick up their telephone and hear everything being said by any other telephone on the line, and anyone could also speak on the line at any time. An incoming phone call would also ring every single phone in the neighborhood simultaneously and anyone could answer it. It was inconvenient, terrible for privacy, could be unusable at times if really talkative users refused to yield the line, and hearing every single phone call not meant for you was incredibly annoying… but at least you *had* a phone if you really needed one.
The original computer networks worked the same exact way as party lines. Back then, you *could* just “split” a cable, plug as many computers as you want into it at any point, and they’d all be able to “hear” one another. But it came with all of the same problems that party lines had. For one, every single computer on the network heard every message sent to every other computer, no matter who it was actually intended for. Polite computers ignored all messages that weren’t them, but any malicious one could simply record all of them. (Public Wi-Fi still works like this to a certain extent, fyi…) Also, if one computer had a lot of data to send, it could tie up the line for a long time and not allow any other computer to effectively use the line, because computers are trash at trying to “talk over” one another without being misheard. But we dealt with the problems for a while, because laying dedicated cable between every pair of machines wasn’t feasible.
So what we currently have at this point is one public space where any computer can talk and be heard. But what we want is every computer to have a private talking space with every other computer. But but, we can’t run cables between every pair of computers on the network, because that would be an exponentially increasing amount of cable, which would be stupid. What can we do to improve?
We compromise! How about, instead of directly connecting every computer to every other computer, we take all the computers and directly connect them to *one* special computer with a ton of ports on it? That way, if I want to send a message from one computer to another, my computer will start up a private conversation with the central computer, which can pass the message on through another private conversation with my target. It would still be quite a bit of cable, but not nearly as much as linking every pair of computers together. Just one new cable for every new computer we add, which isn’t bad. Well, congratulations, we’ve just invented the network switch!
To get back to your original question about splitting Ethernet cables… as you can see, network switches by their very design assume that 1 port = 1 computer. That way, it can hold a dedicated, private conversation with the computer on the other side. Eliminating shared party lines was *the entire point*. What you’d be trying to do by splitting the cable and making two computers “share” a port like that would be re-introducing the party line concept, which would simply fly in the face of how all modern Ethernet networks are designed.
What you *can* do, though, which most other replies have already pointed out, is simply use half of the cable for one connection and half of the cable for another connection. Standard Ethernet cables have 8 wires inside, and older, slower versions of Ethernet connections only used 4 of them. The other 4 are duds. So every piece of cable could, in theory, be used as two separate Ethernet cables that just happened to be bundled together. The catch is that you really do have to treat them like two separate cables–that means two separate plugs at each end, and using two ports on the switch. It was a way to increase utilization of otherwise unused wires, not a way to let two computers talk on the same “line”.
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