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A large-scale network is composed of various types of communication channels. Each communication channel supports quality of service (QoS), which may be different from others. In group communications, each process sends a message to multiple processes while receiving messages from multiple processes. In addition, messages are required to be causally delivered. A process supporting enough QoS receives messages, cannot deliver the messages if another process supporting lower QoS does not receive the 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 synchronization and QoS constraints.