Well, if you were doing a lot of wiring, and wanted to save money, I don't see why you couldn't use telephone type connectors. Just make sure you are consistant and get the polarity correct. You might want to avoid the center two contacts in case soembody plugged in a single line phone. And make the next two contacts be the inbound signal. I had thought of that so that I could wire my home with jacks, but then decided I didn't care if I just had wires coming out of holes in the walls. The official RJ45 wall jacks are a lot more expensive than phone jacks.
If you really want to save money use four line phone jacks. That is, ones that aren't Cat 5 certified but will probably work fine for 10baseT, and if you are a little careful in wiring them at 100baseTX.
Where are you shopping? I've not found RJ-45s to be much more expensive. Also, if you use non-standard connectors, you'll have to create non-standard patch cords, which means you'll be investing a lot of time in making them, instead of buying low cost, ready made cables. You'd also have to worry about plugging the wrong device into the jacks.
Well, that's always going to be true of any electrical connector, isn't it? So you put a cap on it when it's not in use, like
Oh, so you want to run Ethernet plus a bunch of things thru a single multi-contact connector to a box in an automotive environment.
That should be fairly straightforward, keep the pairs together and separated from other pairs, and specify the cables and wiring properly, and all you should have to do is meet the Cat5E spec.
I'd have to guess that any decent Cat5E certification tool will give you crosstalk margins, which will be your main concern. Loss (and length) will probably be nowhere near the spec in a car, unless someone wants to hook a 90M patch cable up...
If they wires of a pair are on adjacent pins, and the impedance is anywhere close to 100 ohms, it should be fine. The effect of connector impedance becomes increasingly important as the wavelength approaches the length of the connector.
I am not sure about the standard itself, but for actual use it is much easier with short cables. The primary problem is attenuation on long cables, which causes the near end crosstalk margin problem. If the received signal is strong the margin will be large even with a lot of crosstalk.
William I have looked at several weathertight RJ45 connectors, but none of them (that I've seen) are very weathertight unless the RJ45 plug is connected. This is for an automotive application and hence robustness is very important. Also, if I can route Ethernet via the main connector I don't need an RJ45 on the box, just one more conveniently located somewhere on the dash.
I will be doing some CAT5 testing on several connectors (reques- ted by customer) although I expect the connectors to work, never theless it will be interesting.