An Adaptable Group Communication System

Existing group communication systems like ISIS, Spread, Jgroups etc., provide group communication in a synchronous environment. They are built on top of TCP/IP or UDP and guarantee virtual synchrony and consistency. However, wide area distributed systems are inherently asynchronous. Existing group communication systems are not suitable for wide area deployment. They do not provide persistent communication; i.e., if a node gets temporarily disconnected, all messages directed to that node during that period are lost. Hence such systems are not suitable for deployment in disadvantaged networks. While, according to Brewer’s CAP theorem, it is impossible for a distributed computer system to achieve the three objectives of consistency, availability and partition-tolerance simultaneously, especially in an asynchronous environment, we present the design and development a reliable group communication system over an asynchronous substrate, where we achieve the objectives of eventual consistency, availability and partition-tolerance. We say that distributed system is eventually consistent, over a long period of time, if no updates are sent and all updates will eventually propagate through the system and all the nodes will be consistent. By availability we mean that if a node failure does not prevent the system to operate continuously. We say that distributed system is partition-tolerant if in the event of network failure that splits the processing nodes which are communicating, then the system should allow the processing to continue in both subgroups