The atomic group protocols: reliable ordered message delivery for atm networks

The Atomi Group Proto ols: Reliable Ordered Message Delivery for ATM Networks by Ruppert R. Ko h The group ommuni ation model has be ome a standard model for appli ations that require a fault-tolerant environment, and many proto ols have been developed to provide the servi es de ned by this model. Most of these proto ols are designed for lo al-area networks, make use of broad ast servi es provided by lo al-area networks, and are e e tive for only a small number of parti ipants. To make the group ommuni ation model available for wide-area networks, spread over a large physi al area, we have developed the Atomi Group proto ol, a group ommuni ation proto ol designed to operate within ATM networks. Being highly s alable, Atomi Group allows thousands of nodes distributed over a physi ally large area to form a single system, ontaining a large number of pro ess groups. The proto ol is designed to provide high throughput and low delivery laten y. Atomi Group is based on timestamps derived from physi al or logi al lo ks. Atomi Group exploits a reliable multi ast proto ol based on sequen e numbers to a hieve reliable message delivery and timestamps to a hive total ordering. The proto ol is re eiver-initiated, whi h provides the lowest laten y in the event of message loss. Positive a knowledgments, piggyba ked on messages, provide bu er management. The use of timestamp a knowledgments helps to keep the a knowledgment overhead small. The maximum laten y of su h a system equals the maximum diameter of the system plus the maximum time between any two message transmissions by the same pro essor. To keep the laten y small, even if there are no messages to transmit, and to dete t faults promptly, the proto ol periodi ally generates null messages. vi