ORBUS Time Synchronization System Based On NTP

Along with the development of Internet, the applications expanded to these domains such as LAN and WAN and Internet have become users'requirements. In order to guarantee that computers cooperate reliably and accurately with one another in distributed computing environment the basic and key issue should be time synchronization. NTP (Network Time Protocol) developed by David L.Mills is proposed. It is in an outstanding position due to its features of self-organizing, hierarchical-master-slave configuration and communication modes applied with different environment. Uniting its'core algorithm, NTP is able to provide distributed systems a service to reach time synchronization with high precision and stabilization. Therefore, it becomes one of the Internet standard protocols with wide uses.ORBUS time system is a service provided by ORBUS middleware, which conforms to CORBA specifications. Time service offers these functions such as simply synchronizing time among computers in LANs and dealing with events based on timer. In the improved version of time service, Cristian algorithm is applied based on network time synchronization of SNTP. The response time error of server requested is improved, and the precision is enhanced. It is able to satisfy all kinds of time synchronizations in LANs.The precondition of the Cristian algorithm is the fact that the request time must be equal austerely to response time in distributed computing environment, especially in the multi-networks or wide area networks. As usual, the difference between the request time and response time is so short, it can be omitted in LANs. Further, the two time values can be considered equal in specified error intervals. But the communication delay fluctuates obviously due to network load or available bandwidth in complicated network environment. Through the above analysis, it is very obvious that the existing ORBUS time service is not powerful enough to satisfy the need of time synchronization among computers in complicated network environment.Considering the expansibility and scalability of ORBUS middleware, and in order to be suitable for heterogeneous compters and networks, the paper proposes a new framework with NTP for time service and implements it. It not only extends the original time service, but also improves the synchronization precision for distributed systems, especially for systems in WANs. The main contributions of the paper are following:(1) proposing a new framework for time synchronization service based on NTP;(2) implementing the filtering algorithm, selection algorithm and intersection algorithm in time service;(3) Testing the time service prototype and analyzing the time synchronization errors in detail.The test results show that ORBUS time synchronization service can provide highly steady time synchronization service in WAN environment. Considering clock error of computer itself, the time synchronization precision of a system is within 100 millisecond. Hence such systems satisfy almost all kinds of applications in distributed network environments.The research work in the paper is supported by project"CORBA Software development"(Grant No: JH02-074), Jiangsu Hi-Tech Development Program for Universities.