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Yes, almost every HDMI cable now brags that it includes ethernet, which is carried on a formerly-unused* pair within the HDMI connector. Many older cables didn
by myself248 7y ago
Yes, almost every HDMI cable now brags that it includes ethernet, which is carried on a formerly-unused* pair within the HDMI connector.
Many older cables didn't connect it, or grounded one of the pins (*because it had been used as a plug-detect pin), but since devices started actually using it, cable vendors started wiring it. The extra pair doesn't make the cable much stiffer, but leaving it out had made them ever so slightly more flexible.
Many devices don't support it, but some newer video cards install an Ethernet device when you load the driver, so they do. And some TVs do, of course. So if such a card and such a TV are connected with such a cable, voila! An connection you might not even realize is there. Your formerly-isolated TV is no longer isolated, assuming the video card driver installer did something like enable bridging to that ethernet interface.
There are a few ways to avoid it. First, don't install that driver if your video card prompts for it, or disable the device. Second, use a cable tester to verify that you're using a cable which doesn't connect the pins, which is gonna get harder if you need a newer cable that's tested to a higher bandwidth spec. Or third, open up the cable and bite the wires in half. It's tricky to know which pins those are; I plan to do it with an inductive "toner" probe connected to a breakout adapter.
(Unrelated: Some Ethernet switches used HDMI cables to connect each other for "stacking". This is just because the connectors are cheap, the cables are cheap, and they have a lot of high-bandwidth pairs. The switch makers could run more-or-less full backplane speeds over a short HDMI cable more cheaply than they could over a custom stacking cable. But the signals on the wires are not HDMI, they're more-or-less Ethernet on whatever inter-switch-chip format, probably QSFP or something, that needs a bunch of length-matched pairs.)