Publish-Subscribe makes sense for the messages.
Discussed message structure further. Headers as additional information added by network nodes. Messages need globally unique identifiers (UUCP hash of path raised as a concern for identifying messages after creation. Alternatives: Message with elements added to header (id, timestamp, potentally interested subscribers as identified by node). Message in wrapper with these elements added to wrapper. Message with unique id and other messages that describe this message - last seems problematic for scalability, resolvability, and using messages to route other messages.
Parenthetical note, use of HISPID3 interchange is shown nicely in diagram on http://www.chah.gov.au/chah/avh-info/avh_presentations/avh-hiscom-00-11/
Worked on abstract. Revised component diagram to fit: File:Component2.zip