Group Communication System Over IP Multicast

New applications such as distributed conferencing system, shared whiteboard, remote learning, cooperative work and Internet-based games have already emerged. Because there are multiple nodes attending the computing at the same time, it's been shown that traditional point-to-point transport protocols are not suitable to construct such applications. Group communication is a mechanism that can provide one-to-many and many-to-many tranport service, and it has widely been used to support fault torlerant system. In this paper, we propose to combine group communication mechanism and network layer multicast(IP Multicast) to build these distributed applications.The paper describes the service semantics of group communication and details the implementation of these services. Traditional group communication systems just provide group and member management and message delivery service. Here, synchronization is considered in the group communication layer.We discuss four parts of the group communication. Fisrt, group and member management. IP Multicast address is used to identify a group. Group member is identified by (IP Address,Member ID) tuple. It uses a simple failure detecting and membership consistency method to deal with the membership management. 2.Message delivery. Message delivery service is the pivot of this paper and concerns 3 problems, reliability, ordering and byte/message oriented service. We use sequence number of TCP to realize the FIFO order. In dealing with the causal order, spontaneous sending event and passive sending event are differentiated. We initiate the Requesting Token Algorithm to solve the total order and synchronization of distributed processes. 3. Synchronization. A method to solve the token losing and process starvation is provided. 4.Security. We only give the issues that should be considered in group communicaiton environment. Its implementation would be future work.Although the group communication uses IP Multicast in network layer, it does not depend on multicast routing. So flexibility could be achieved, because when the routing algorithm changes, there is no need to redesign the group communication layer. After describe the implementation of the system, we compare the group communication with TCP/IP protocol, and find that if we take the group communication as a layer of protocol stack, it corresponds to the TCP layer. So in fact, the group communication provides transport layer service.