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
If an Ethernet splitter is used, the connection needs to be UN-split at the other end in order for the device to work properly.
Those devices take advantage of that 100 Mbps ethernet only uses [half the wires](https://o.quizlet.com/uJPiue-vL4u2QnPsga3RRg_b.png) in the cable. So you can use an 8-wire ethernet cable to carry two connections that only actually need 4 wires each.
It’s a stupid idea in this day and age. Gigabit and above require all 8 wires for a single connection. Just buy a dirt cheap gigabit switch on each end. You can get those for about $10.
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When you look at a cable like a basic Cat-5 Ethernet cable what you’re really seeing is a collection of 8 smaller (colored) wires all bundled together. Each of those individual wires connect to a pin in the terminal clip that you plug into the Ethernet port and hardware at both ends are expecting certain data from that pin. A lot of uses for the whole cable only uses 4 of those wires. So basically your splitter is separating those pins into two sockets, and you need a splitter on the other end to make sure the data from each wire goes to the right place.
It’s much like an 8 lane interstate highway. A bunch of cars coming from different places but going the same general direction for a while merge onto the highway. But they all eventually have different destinations so they need to be split back off into separate roads.
Ethernet is point to point. A cable has 4 twisted pairs – 8 wires.
In connections less than 1GbE only 2 pairs – 4 wires are used. 2 wires for sending, 2 for receiving.
The splitters let you utilize the 4 unused wires on the cable, but still need a dedicated port to connect to.
1GbE uses all 8 wires and as such you couldn’t successfully use a splitter.
The splitter uses the wires in the cables and uses half of the available wires for each port. The second splitter reverses this in a consistent manner such that it is useable for Ethernet.
Effectively the quality of the cable reduces, and the speed of the link will drop to compensate for the reduced quality.
It may be helpful to remember that Ethernet is both sending and receiving data.
Now picture a splitter in the shape of a Y with a single port on the bottom and 2 at the top. You could argue that taking data from the bottom and sending it up could work as it would just be sending the same information to 2 places.
Where this all falls apart is going the other direction. Anytime you send data from the top of the Y down, it just turns into a jumbled mess when it hits the base of the Y.
A ‘switch’ for all intents and purposes is essentially a smart splitter, it takes the information that it gets from each of the Ethernet ports, repackages it slightly and sends it down the line to avoid the jumble.
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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