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In this paper, we propose an information model supporting maintenance schedule coordination that flexibly accepts operators' requirements without any impact on other classes.As management functions advance, reduction of the construction costs of network management systems (NMS) and shortening of construction times become increasingly serious problems in telecommunications management. Many contributions to this field, such as the work of the TeleManagement Forum, focus on the development of common software components and a plug & play scheme in order to solve these problems. In the case of system construction using these components and scheme, the way in which operator requirements are embedded in the NMS is important if the system is to be useful to operators. Since the construction of NMS is based on information models, these models are required to be flexible in terms of their ability to accept customization.In this paper we propose a flexible information model supporting maintenance schedule coordination that is a management function used to prevent the suspension of services in accordance with the operator's particular requirements. This model is designed for telecommunications networks that aggregate various kinds of communications and are required to fulfil various criteria in terms of reliability, delay, and bandwidth. The operator has to consider constraints concerned not only with securing an alternative route, but end user requirements involving application system operations that change dynamically.This information model is designed using the strategy pattern and state pattern in order to prevent customization of an object class from modifying content in other classes. These two patterns have been proposed as solutions to design problems in object-oriented design. The strategy pattern provides a framework that encapsulates each algorithm and makes it exchangeable, and it is said that a designer can modify algorithms independent of client objects. The state pattern enables an object to select behaviors according to the object's intemal state. This facility is made possible by the introduction of classes representing states. Figure 1 illustrates the proposed information model as object diagrams of Unified Modeling Language (UML). There are five basic classes in the model. A work class models maintenance suspending the functionality of network elements. A network element class represents an abstract component of networks, such as a link or a node. An application system class represents the system providing services used by end users, and includes attributes concerned with service level agreements. A 0-7803-5864-3 0 2000 IEEE

In this paper, we propose a communication method with IP-based wide area networks for SCADA systems. This method controls communications between substations and a control center and can be implemented as a communication middleware. The method supports functions for UDP-based transmission, route control of double route transmission, retransmission control and priority control. The functions work cooperatively to assure reliable and real-time communications. We also examined the effectiveness of the method under circumstances where there are not only transmission delay and route breakdown in network but also information congestion in computer. The results show that the proposed method is more effective for assuring real-time and resilient feature than TCP-based communication method.