> Because it pushes the flow control out of the kernel (and possibly network adapters) into userspace
That’s not an inherent property of the QUIC protocol, it is just an implementation decision - one that was very necessary for QUIC to get off the ground, but now it exists, maybe it should be revisited? There is no technical obstacle to implementing QUIC in the kernel, and if the performance benefits are significant, almost surely someone is going to do it sooner or later.
also looks like current quic performance issues are a consideration, tested in section 4. :
> The performance gap between QUIC and kTLS may be attributed to:
- The absence of Generic Segmentation Offload (GSO) for QUIC.
- An additional data copy on the transmission (TX) path.
- Extra encryption required for header protection in QUIC.
- A longer header length for the stream data in QUIC.
Windows already has an in-kernel QUIC implementation (msquic.sys), used for SMB/CIFS and in-kernel HTTP. I don’t think it is accessible from user-space - I believe user-space code uses a separate copy of the same QUIC stack that runs in user-space (msquic.dll), but there is no reason in-principle why Microsoft couldn’t expose the kernel-mode implementation to user space
No one ever uses SCTP. It's pretty unclear to me why any OSes do include it; free OSes seem to like junk drawers of network protocols even though they add to the security surface in kernel land.
SCTP is exactly how you establish a data communication link with the very modern WebRTC protocol stack (and is rebranded to "WebRTC Data Channels"). Granted, it is SCTP-over-UDP. But still.
So yes, SCTP is under the covers getting a lot more use than it seems, still today. However all WebRTC implementations usually bring their own userspace libraries to implement SCTP, so they don't depend on the one from the OS.
Does anyone even build SCTP support directly into the kernel? Looks like Debian builds it as a module, which I'm sure I never have and never will load. Security risk seems pretty minimal there.
(And if someone can somehow coerce me into loading it, I have bigger problems.)
Linux and FreeBSD have had it for ages. Anything industrial too. Solaris, QNX, Cisco IOS.
SCTP is essential for certain older telco protocols and in certain protocols developed for LTE it was added. End users probably don't use it much, but the harsware their connections are going through will speak SCTP at some level.
That’s not an inherent property of the QUIC protocol, it is just an implementation decision - one that was very necessary for QUIC to get off the ground, but now it exists, maybe it should be revisited? There is no technical obstacle to implementing QUIC in the kernel, and if the performance benefits are significant, almost surely someone is going to do it sooner or later.