Hmmm, I remember no such decision and think it isn't a particularly useful
way to define TTL. The sender couldn't care less when a receiver MSH gets a
message, they care only about the application at the To Party.
As you comment, the underlying issue is (again) acknowledgments and their
semantics. I completely agree an acknowledgment message MUST be the last
message an MSH could initiate with reference to a received message. (Yes,
applications are free to respond to any message whenever they please -- I'm
talking only about MSH signals.) In particular, error messages (such as
"TTL expired") MUST NOT be sent after an acknowledgment message has been
sent. According to my understanding of TTL, this would mean an MSH
shouldn't send an acknowledgment until it has informed the application.
whatever,
doug