Quite possibky sonething that has been discussed before, i’m not sure. I thought i recalled someone saying this before, but I was trying to have a quick look (a very quick look at that) at the USB C spec, and there doesn’t seem to be anything in the spec for USB C - C extension cables.
I don’t know if I’m just being thick and not understanding what I was reading, but USB C -C extension cables are deviating from spec right?
As far as I know USB 2.0, 3.0, 3.1 etc didn’t need it in the spec due to the nature of the connectors, and extenders we’re all fine?
Thinking about it too, with my limited underatanding its also possibly very dangerous with USB PD too, since the handshake is with the mating connector and not the end point?
Assuming I’m not being completely thick and misunderstanding anything, is this just daft oversite not including this coverage in the spec, malace in trying to make more money from licencing fees up where people need to buy more cables at thebcorrect lengths lengths, or something else entirely?
Can someone help me understand if I’m wrong, or why this seems to be the case?
You’re right about the issue being with the handshake that previous versions of USB didn’t have.
It’s the USB-C cables themselves that have a chip that takes part in the handshake and AFAIK USB-C extension cables are just wires. So if using an extension the speed, power handling and video capabilities negotiated by the cable being extended may not be accurate.
I imagine adding support for extension cables would have significantly complicated the negotiations, especially with multiple extension cables in the same run.
If only used to connect devices that use little power and low speeds then using a single extension will probably work… as long as the ratings of the extension exceed the cable being extended. Best to not use an extension to extend cables with high power ratings though because extensions will just pass on the high power rating despite the additional length and the additional connection reducing the power handling capability.
Most long range extensions are either fiber converters or ethernet converters, and to deliver PD they use a power adapter at the end. They work fine and get you a long distance. I have also seen USB C extension cables in 6-10’ range as well that have a female end for the original cable to go in. I havent looked at the spec itself to see if these are specifically allowed by it or not, but I dont see why the spec would ban them as long as they meet the specification requirements as far as functionality, interopability, and bandwidth.
It’s more of a longstanding policy thing as, so far as I know, external passive extension cables have been out of spec since USB 1.0. But… type E has an implementation document and IDM 20-pin has an Intel spec. Both of these define extension cables. So it seems a bit difficult to argue plugging a C-C extension cable compatible with type E into a rear USB-C would be much of a functional deviation from spec. (There should be a similar spec for USB 2.0 IDC cables but I’m not having luck googling it up.)
Active extension cables are treated as one port USB hubs for spec compliance purposes, I believe.