announcement is an (ID, value) tuple that is disseminated to local
area neighbors. An application or protocol can explicitly listen to
announcements from neighbors. When an announcement is heard, a
callback is invoked.
Announcements can be used for a variety of network mechanisms such as
neighbor discovery, node-level service discovery, or routing metric
dissemination.
Application programs and protocols register announcements with the
announcement module. An announcement back-end, implemented by the
system, takes care of sending out announcements over the radio, as
well as collecting announcements heard from neighbors.
