Strong reliability properties

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In the context of multicast protocols, strong reliability properties express the guarantees that the protocol provides with respect to the delivery of messages to different recipients.

An example of a strong reliability property is last copy recall, meaning that as long as at least a single copy of a message remains available at any of the recipients, every other recipient that does not fail eventually also receives a copy. Strong reliability properties such as this one typically require that messages are retransmitted or forwarded among the recipients.

An example of a reliability property stronger than last copy recall is atomicity. The property states that if at least a single copy of a message has been deliverd to a recipient, all other recipients will eventually receive a copy of the message. In other words, each message is always delivered to either all or none of the recipients.

One of the most complex strong reliability properties is virtual synchrony.

Strong reliability properties are offered by group communication systems (GCS) such as ISIS, Appia framework, Spread, JGroups or QuickSilver Scalable Multicast. The QuickSilver Properties Framework is a flexible platform that allows strong reliability properties to be expressed in a purely declarative manner, using a simple rule-based language, and automatically translated into a hierarchical protocol.