DisplayPort 2.1b (active) compatibility with DisplayPort 2.1a monitor

Wyllio · January 16

This might be early, but I want to get this question out there before more of the new monitor reviews drop, as I have not seen anyone ask about compatibility. DisplayPort 2.1b was announced during CES and is present on the Nvidia 50 series GPUs. It uses a new active cable standard called DP80LL, which currently is stated to allow up to 3m long cables. The current 2.1a standard only has one listing up to 2m that is VESA-certified. Multiple new monitors were also announced at CES with the latest Samsung 27" 4k 240hz panel and finally using DP 2.1a.

When a 3m DP80LL active is plugged into a monitor using a DP 2.1a port, does it still receive the full 80 Gbps bandwidth? Does the cable default to a lower-rated standard such as UHBR 13.5/UHBR 10 and utilize DSC? Or does the new standard and cable only require the GPU side to power the active cable? The current max cable length of DP 2.1a is a big limitation for adoption as there are plenty of times when the monitor is not as close to the PC or is only a monitor arm and needs extra slack to move freely. If the DP 2.1a is not compatible with the new active cable standard then that could be a deciding factor for some people to wait until 2026 and beyond before purchasing a new monitor.

Doobeedoo · January 16

The DP 2.1 spec for cables the a adds longer passive cable support and b further longer cable being active. The spec is said to be released at spring.

https://www.displayport.org/pr/vesa-to-update-displayport-2-1-with-new-active-cable-specification-for-up-to-3x-longer-dp80-cables/

https://vesa.org/press/vesa-to-update-displayport-2-1-with-new-active-cable-specification-for-up-to-3x-longer-dp80-cables/

Wyllio · January 16

I've already seen and read the article. It does not clarify whether the updated spec is just for the active cable or both the cable and port. Their wording isn't clear but it seems like they are referring to the release of the new cables in Spring as technically Nvidia's 50 series will have DP 2.1b by the end of January.