NFD

Notification rev7 gives two subscriber workflows. First workflow requires "ChildSelector=rightmost Exclude=any,last-know-seq-num" in every Interest. Second workflow requires "ChildSelector=rightmost MustBeFresh=yes" in first Interest, and uses incrementing sequence numbers in subsequent Interests.

I think the most straightforward solution is:

• Subscriber sends CanBePrefix=yes MustBeFresh=yes for the first Interest, and uses incrementing sequence numbers in subsequent Interests.
• Publisher sets minimum FreshnessPeriod.

While RDR protocol (#4706) is attractive, it's overkill for Notification Stream. RDR allows high FreshnessPeriod on application Data, and uses a short-lived metadata packet to inform consumers what's the latest application Data. NFD Management's notifications are short-lived and there's no benefit in setting high FreshnessPeriod on notifications, and therefore subscribers can directly retrieve notifications in the same way they retrieve RDR metadata.

PSync is another possible solution, but it's also overkill for Notification Stream. PSync allows subscribers to get updates about multiple data streams, while NFD Management only has a handful of notification streams, so it's not worth the overhead of adopting PSync.

Notification rev8

LGTM