Experience with the AMp group communication system: Current status

A communication architecture, named AMp, which supports, through the adequate protocols, a reliable communication service featuring several order, distributed-agreement, synchronism, and group management properties, is presented. In this local computer network model, host computing units are interconnected, through a broadcast channel, by means of network attachment controllers (NACs). Each host NAC set is a node. The NACs plus the channel are an error-containment domain: they ensure a dependable communications service to the hosts. They also are a performance-containment domain. The decoupling of NACs from the hosts aims at enforcing that containment and offering a host-independent interface (e.g., a standard backplane bus). The NAC is said to be fail-silent: it is confined to always delivering correct messages and halting after its first failure. The above-mentioned properties are materialized by a two-phase accept protocol, whose simplicity allows an efficient implementation. In practice the protocol works like a commit protocol. Most of the actual implementation work has been carried out within the scope of the Delta-4 project. The Delta-4 system is an open, dependable distributed architecture. The Estimulo project, which is aimed at exploring new concepts in the design of distributed office systems, not excluding business and scientific applications, is also outlined.