Research And Implementation Of Reliable Multicast In Cooperative Design System

As an application of Computer Supported Cooperative Work (CSCW) to Computer Aided Design (CAD) field, Cooperative Design is an important direction of currently researching in computer application. It is unavoidable that information is exchanged among multi-participators, and the same information is transported from one to other participators at the same time. The traditional unicast and broadcast can't meet the demand of point to multi-points communication for Cooperative Design, IP multicast is the novel transport protocol to solve this question. It permits that a source in the network once delivers a packet to an arbitrary number of receivers. So it can retrench the network resources and enhance the transmission efficiency. However, IP multicast make use of UDP protocol to deliver datagram on the transport layer, which only provides a "best effort delivery" service, so this protocol can't sure the reliability of data transmission. But the data transmission of Cooperative Design demands the perfect reliability, so some necessary error control methods used in application are indispensable to realize the reliability of data transmission.According to "Framework of Cooperative Design System" proposed by the Center of CAD Eng. Southwest Jiaotong University, this thesis analyses the relation between cooperative design system and communication service module, and also puts forward the structure of communication service module in the cooperative design system. This thesis discusses detailedly the flow process of IP multicast, error discovery method and error recovery method, and also proposes a new error control method to implement reliable multicast in Computer Supported Cooperative Design System: serial integrates with timer are used to discover error, ARQ mechanism based on NAK feedback is modified to correct error, "Sliding Window" mechanism is imported to make up the drawbacks of traditional NAK, and "slotting and damping" technique is used to resolve the question of "feedback implosion" which results from multicast reliability control. At last, function modules of the foregoing are implemented in the reliablemulticast program, which provides reliable multicast communication for Cooperative Design System.Research on the reliable multicast is a key technology to support CSCW, and has an important practical significance for the development of Cooperative Design System. At present, the problem on reliable multicast transmission is being investigated yet, and don't come into being a uniform standard. As a part of the national 863 planned project-"2001AA411320 regional modern integrated manufacture system development and application oriented city Chengdu, Deyang and Mianyang" and the science and technology key project of Sichuan Province-"the engineering configuration Intelligent CAD technology oriented the process of design", this thesis proposes a modified scheme, which restrains efficiently the "feedback implosion" question, and is able to realize the reliable multicast. This scheme has considerably academic and practical significance.