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Most existing communications technologies are either not scalable at all, or scale only under carefully controlled conditions. This threatens an emerging generation of mission-critical but very large computing systems, which will need communication support for such purposes as system management and control, policy administration, data dissemination, and to initiate adaptation in demanding environments. Cornell University's Spinglass project has discovered that "gossip-based" protocols can overcome scalability problems, offering security and reliability even in the most demanding settings. Gossip protocols emulate the spread of an infection in a crowded population, and are both reliable and stable under forms of stress that can disable more traditional protocols. Our effort is developing a new generation of gossip-based technology for secure, reliable large-scale collaboration and soft real-time communications - even over global networks., International Survivability Conference and Exposition. DARPA DISCEX-2001, Anaheim, California, June 2001. Sponsored in part by DARPA and NASA. U.S. Government or Federal Rights License

The Horus and Ensemble efforts culminated a multi-year Cornell research program in process group communication used for fault-tolerance, security and adaptation. Our intent was to understand the degree to which a single system could offer flexibility and yet maintain high performance, to explore the integration of fault-tolerance with security and real-time mechanisms, and to increase trustworthiness of our solutions by applying formal methods. Here, we summarize the accomplishments of the effort and evaluate the successes and failures of the approach., Sponsored in part by ARPA/RADC grant F30602-98-2-0198. Presented at the DARPA Information Survivability Conference and Exposition (DISCEX '00) held in Hilton Head, SC on 25-27 January 2000. Published in the Proceedings of the DARPA Information Survivability Conference and Exposition (DISCEX'00), 2000.

To deliver multicast messages reliably in a group each member maintains copies of all messages it sends and receives in a buffer for potential local retransmission. The storage of these messages is costly and buffers may grow out of bound. Garbage collection is needed to address this issue. Garbage collection occurs once a process learns that a message in its buffer has been received by every process in the group. The message is declared stable and is released from the process buffer. This paper proposes a gossip style garbage collection scheme called GSGC for scalable reliable multicast protocols. This scheme achieves fault tolerance and scalability without relying on the underlying multicast protocols. It collects and disseminates information in the multicast group by making each group member periodically gossip information to a random subset of the group. Extending the global gossip protocol further this paper also investigates a local gossip scheme that achieves improved scalability and significantly better performance. Simulations conducted in a WAN environment are used to evaluate the performance of both schemes., Sponsored in part by ARPA.