Code change:
elapsed time between the acknowledgements for specific TCP segments from a TCP receiver since TCP octet sequence numbers and acknowledgements for those sequence numbers are carried in the clear, <del> even if the TCP payload itself is encrypted.  See tcp-behavior for more information. </del> <ins> even if the TCP payload itself is encrypted.  See reliable-behavior for more information. </ins> As transport protocols evolve to encrypt their transport header fields, one side effect of increasing encryption is the kind of passive monitoring, or even "performance enhancement" (RFC3135) that was possible with the older transport protocols (UDP, described in <del> udp-behavior and TCP, described in tcp-behavior) is no longer possible with newer transport protocols such as QUIC (described in quic-behavior).  The IETF has specified a "latency spin bit" mechanism in Section 17.4 of RFC9000 to allow passive latency </del> <ins> unreliable-behavior and TCP, described in reliable-behavior) is no longer possible with newer transport protocols such as QUIC (described in quic-behavior).  The IETF has specified a "latency spin bit" mechanism in Section 17.4 of RFC9000 to allow passive latency </ins> monitoring from observation points on the network path throughout the duration of a connection, but currently chartered work in the IETF is focusing on endpoint monitoring and reporting, rather than on passive

Related discussion:
text: …transport protocols Also tighten up description of the assumed protocol stack in (what is now) Section 6.1. Note that the UDP and TCP sections have been flipped in order, to improve section flow and clarity.
NAME - If you have a moment before our call on Friday to take a look at this PR, I'd appreciate it. I think it's important to to get that right, in order to address both the INTDIR and TSVART reviews.
From NAME As a bit of transport commentary, I don't find the setup of Section 6 compelling. While UDP is a transport in a technical sense, for the purpose of media, it is almost always a layer upon which the protocol doing the congestion control work runs. To that end, QUIC is just another more standardized case of this, just like SCTP over UDP. Rather than talking about "UDP's behavior" vs "TCP's behavior", I suggest talking about how applications over UDP for media behave vs applications over TCP for media behave.
NAME - I need to look at this more closely. I understand your point about UDP, but (because UDP is not a real transport layer, while TCP and QUIC are), I suspect (without looking closely yet) I'm going to be making sure that I explain this more clearly, without trying to explain the behavior(s) of applications running over TCP and QUIC. As an aside, I'm trying to make this clearer in drafts I'm targeting forwards Media Over QUIC/MOQ, so I actually DO believe you ... Please await results.
A +1 from NAME 's review (URL): Section 6. Evolution of Transport Protocols and Transport Protocol Behaviors I really wonder whether UDP vs. TCP vs. QUIC is actually the relevant distinction. What may actually matter are the transport services provided by the protocol stack (e.g., RFC 8095). I fully agree to a related comment in the INTDIR review.
After looking at this issue. I agree with both NAME and NAME that the emphasis should be on the interaction between (see new section describing this) media transport protocols and the transport services provided by underlying transport protocols. I'm moving the formerly-UDP section below the formerly-TCP section, because it's easier to describe what UDP is NOT doing after describing what TCP IS doing.