Due to some annoying technology issues (which are worth a pit thread I don’t feel like starting), I’m looking for a y-adaptor for a Cat5 or Cat5e patch cable and LAN connection. I assume that doing such a thing would effectively halve the bandwidth, but that’s okay as it’s (with any luck) a temporary fix and I don’t feel like getting a router or anything set up. I can’t seem to find anything online that says to me “Yes, this is exactly what you need.” Should I be looking for an RJ45 y-adaptor instead of a cable type? A switchbox isn’t quite the right solution, as I need both connections up simultaneously, unless it can do automatic switching (at which point aren’t we just talking about a router?) Am I on the right track, or is there something else I should try?
If you’re looking to connect two different computers to one broadband connection device to access the internet, what you suggest will not work, even if you can find one. For that, you need a router. You can find them fairly cheap. I bought an off-brand 4-port unit on eBay a while back for about $10.
More like a hub.
A hub is basically a splitter for Ethernet. You plug a bunch of network cables into it, and any packet that comes in one port is echoed out the other ports.
A switch is a smart hub. It remembers which computers are attached to which ports, and it looks at the destination for each packet, so packets are only sent to the ports where they need to go. This improves network performance and security.
A router is one step smarter. It doesn’t just know how to read Ethernet packets, it knows how to read the internet packets stored therein, and can filter packets based on their IP addresses or TCP/UDP port numbers. Most routers can also do stuff like NAT, which is what you’d need to share a broadband connection.
If you just need to connect an extra computer to your LAN - say you have an office with one RJ45 jack and you need to hook 2 PCs up to it - then a hub will be fine. I don’t know if any Y-connectors exist, but it seems to me like they should work, since the original idea of Ethernet was for multiple devices to share one electrical connection.
We need a little more info about your situation to offer a cogent solution, but QED is correct. A simple 2 to 1 Y splitter will not work properly with an ethernet topology. Basic hubs, switches and routers are super cheap on eBay. You can probably get what you need for 15. or so. for a switch or hub, and less than 40 for a router.
Not quite. The so-called ‘thin ethernet’ (using a thick coax cable, but not as thick as ‘thick ethernet’) was indeed a physical ring network, and there it was easy to add a new computer to the loop.
Nowadays, with 10-base-T (and 100/1000-base-T) the physical topology is a point-to-point network, which requires straight (but twisted) cables between two devices. Logically it is still a ring, but the cables don’t know that… 
Bottom line: Get a hub!
Interesting. I stand corrected.
QED nailed what I was looking for. (I’d also like to get my PS2 online if I ever get around to getting a network adaptor, so I guess I’d need a router even if they finally fix the other port.)
In the interest of full disclosure, we sometimes use these devices at the University where I work. Each student room has 2 ethernet ports, wired to a closet with a switch where they’re patched in. If a room port goes bad (say, because somebody sticks a screwdriver into it) and we don’t have time to take the box apart and punch down a new port (because it’s a pain in the ass) we’ll split the port temporarily. It allows 1 cat5 wire to carry 2 ethernet signals.
You have to put one on each side of the wire and patch to 2 ports on the switch/hub on one end and to the 2 computers on the other end. You really only need 2 pairs to run ethernet and this device allows a different device to use each pair. The downside for your situation is the price! You can buy a hub for cheaper.
I put a picture of one here which more clearly shows the wiring diagram.
Nope: Ethernet is a bus network. Connecting the ends of Ethernet coax together would be a bad thing. Note that Ethernet of all forms is a bus network conceptually. With 10x-BaseT the physical appearance is tree-like, but as far as the networking protocol goes, it’s still thinks it’s a bus.
In the interest of full disclosure, it allows 1 cat5 wire to carry 2 crappy ethernet signals, because it splits the pairs of wires between two different plugs. I know you can’t do 1000T with that, not sure if you can do 100T (connector says “10bT” on it). Can you even do full duplex?
-lv
100BaseT only uses two pair, so there’s no reason why it should be any crappier than a pair of Cat5E runs.
There are (or I’m sure there used to be) such things as passive ethernet splitters that worked on the principle that collisions were tolerable - I’m sure I saw one in a catalogue a long time back (I’m also pretty sure it wasn’t just a port splitter like the one described by LateComer.