-Causality in Wide-Area Group Communications

In distributed applications, a group of multiple processes cooperate by exchanging multimedia messages. It is critical to support the group of application processes with enough quality of service (QoS) in addition to the ordered delivery of messages. The delay time and the message loss ratio are signi cant QoS parameters. In the Internet application, the delay time and the loss ratio are signi cantly di erent in di erent communication channels. We de ne a novel causality named -causality among the messages to hold in the world-wide environment. We discuss how to transmit messages to the destination processes and how to resolve the message loss and delay supporting the -causality given the requirements of delay time and message loss ratio.