A Study On The Reliable Multicasting Applicable To Collaborative Virtual Environment

Collaborative virtual environment(CVE), which integrates various computer techniques including virtual reality, computer network, and computer supported cooperative work, provides users with shared virtual space to interact and collaborate with each other in a more natural and harmonious way. It is becoming the trend of next generation computing collaboration application, and being gradually applied to digital entertainment, distance education and simulation of real world.In the procedure of collaborative, virtual environment information and mass interactive operation and control need to be transmitted to every participant efficiently and reliably. Meanwhile, it is required that communication protocols should be able to reduce the load of backbone network, improve throughput and handle network congestion efficiently. Based on the researches on communication protocols, communication mechanism of CVE and the practical application of collaborative virtual environment, we propose a feasible reliable multicast protocol (SSMRMC) based layered structure and error recovery channel mechanism, which is on the basis of analysis on other's research works about collaborative virtual environment and reliable multicast.Our main research work and productions are listed as follows:①PIM-SSM mechanism is used in SSMRMC to reduce the number of multicast address. In PIM-SSM mechanism, a multicast-tree is constructed by SPT and avoids the possibility that the RPs in PIM-SM protocol are bottleneck of network.②In routing means of SSMRMC, error recovery channel is used to retransmit the missed packets, thus reduce the load of receivers and improve the throughput of protocol.③There is a source-specific multicast mechanism, based on PIM-SSM mechanism, be drawn into SSMRMC protocol. A triad which determined by sender address, multicast-group address and packet number, provided by source-specific multicast can resolve the cross-passing problem produced by multiple senders in CVE. Furthermore, the triad can be the basis of ensuring that receivers can receive ordered packets.④In SSMRMC, the participants of CVE are divided into global group and several local groups. In this way, the error handling and packet retransmission are limited in the local groups to balance the load and localize the error recovery. ⑤In each local group, one node that is charactered as great processing power and optimum network performance is selected for taking charge data packet through weighted by choice;And to value the sub-optimal nodes as candidates for management, in order to avoid the collapse for the failure of nodes, and so on.Finally, the author carries on the simulation for the proposed protocol based on fundamental research. The outcome shows SSMRMC can satisfy application request of CVE, effective guarantee the arrival of multicast data in sequence and multicast data's arrival according to sequence and the network load reduction in the many-to-many communication, and solve uniformity, responsiveness, expansion in application of CVE.