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> the UDP protocol wasn't optimized by routers and operating systems over the last decades due to its low usage, making it comparatively slower than TCP

What exactly does this mean?

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I haven't read the article yet but I think that means that UDP was used less than TCP and so routers/operating systems didn't optimize for it as much as they did for TCP. Hope this helps.

Right that’s all it says on this subject. I am curious about what optimizations TCP has benefitted from that we’re not but could be applied to UDP.

For example various kinds of hardware TCP offload, like:

1. Handing the NIC a single blob of data (> MSS) in a single operation, and having the NIC do the segmentation into multiple packets.

2. Having the NIC detect multiple exactly consecutive TCP packets on the same flow, and merging them to a single receive operation.

Hardware offload is impossible to do for UDP, since neither the NIC or OS can assume anything about the payload semantics.

there's nothing to optimize with UDP, you put a datagram on the wire and off it goes. There's no sequence number like in TCP to re-order and construct a stream on the receiving side. There is no stream, it's UDP. You put a datagram on the wire and that's it. There no syn/ack either so no congestion control in routers, no back-off or anything.

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