datagrams

Most UDP applications wouldn't just blat their data directly into UDP datagrams, just like almost nobody blats their data directly into IP datagrams.

The timeout is checked only after the receipt of each datagram, so that if up to vlen-1 datagrams are received before the timeout expires, but then no further datagrams are received, the call will block forever.

The article is testing the reliability of the internet to deliver datagrams.

Routes are routes and datagrams are datagrams to them.

Here you're describing a bunch of possible properties a hypothetical protocol written on top of unreliable datagrams would/should have.

It's a shim on top of IP to let unprivileged users send IP datagrams that can be multiplexed back to the right user.

UDP (and datagrams in general) are not the only alternative to TCP-over-TCP.

Even if you encrypt the datagrams, what stops someone from replaying them?

If the tool explicitly provided message authentication for the UDP datagrams, I would probably not have made the same comment.

You'll get fragmentation on every segment over 1460 bytes, which would be the majority of datagrams for a large file upload like pictures or movies.

That's why the Internet does not guarantee delivery of IP datagrams.

Just because your stack can reassemble 64KB datagrams, don't assume that you want to spend more than about 4KB of state memory per ongoing transaction.

UDP was actually "designed" in 30 minutes on a blackboard when we decided pull the original TCP protocol apart into TCP and IP, and created UDP on top of IP as an alternative for multiplexing and demultiplexing IP datagrams inside a host among the various host processes or tasks.