Atomicity and causality of multimedia messages in group communication

A large-scale network is composed of various types of communication channels. Here, each communication channel supports a different quality of service (QoS). In group communication, messages are required to be causally delivered. Even if a process supporting enough QoS receives messages, the process has to wait to deliver the messages until another process supporting lower QoS receives the messages in order to realize the atomic and ordered delivery of messages. Thus, multimedia data cannot be delivered to processes so as to satisfy the real-time constraint if a slower process is included in a group. We discuss group communication protocols by which multimedia messages can be delivered to a process with some time constraint properties which satisfy the QoS requirements of multimedia messages.