The difference between Figure 2 and Figure 3 is rather subtle.
I actually diffed the figures to find it. My understanding is that
it is really only the labels t0 and t1 and e0 and e1. One could
perhaps change the figures to make it more explicit when t0 (e0)
take place, perhaps also clarifying the text a bit. There is perhaps
some confusion caused by the notion of time t0, t1, the notion of
events e0, e1, and the notion of tag values labeled (t0) and (e0).
The text says "The server verifies freshness by checking that e0
equals e1, where e0 is the cached value when the Echo option value
was generated, and e1 is the cached value at the reception of the
request." I found this confusing. It think what you are trying to
say is that the tag value cached at event e0 is the same as the tag
value received at event e1, no?
That's good input; we're going through a few versions among the authors
for the precise visual alignment and wording.
What I'd like to take away from that is to make the events more visible, use shorter Echo values (as event-based can use), and give concrete values both for time and events (given it's an example, and maybe even to use the event state in the echo value).
From https://datatracker.ietf.org/doc/review-ietf-core-echo-request-tag-11-opsdir-lc-schoenwaelder-2020-11-30/ :
That's good input; we're going through a few versions among the authors for the precise visual alignment and wording.
What I'd like to take away from that is to make the events more visible, use shorter Echo values (as event-based can use), and give concrete values both for time and events (given it's an example, and maybe even to use the event state in the echo value).