Generic Announcement Protocol for Event Messaging

We describe the Generic Announcement Protocol (GAP), a two-tier generic multicast transport designed for scalable event notification. GAP requires no extra central infrastructure or administration beyond a multicast enabled network or an equivalent overlay. GAP’s scalability arises from the use of announcement indexes, which exploit the underlying openness and flexibility of the raw GAP protocol. Event notifications can be massively multiplexed onto a multicast group channel, with interested receivers only joining the group for the brief duration of the announcement, coordinated by an acyclic graph of indexes, which are themselves announcements on other channels. This indexing technique, combined with the GAP protocol is particularly efficient when waiting for events to occur, since the network resources (for addressing and filtering) are kept to a minimum.