| Internet is developing by leaps and bounds. Along with the commercial operation of 3rd Generation (3G) mobile communication networks and the construction of WLAN networks throughout major cities, Internet will come into wireless and mobile age soon. Taking this opportunity, Internet applications will usher in a new wave of development. Distributed monitoring system is a data acquisition system or information collection system constructed on computer network, which can acquire the status data of monitored objects at dispersed spots rapidly for their centralized supervision and management through deploying various networked monitoring terminals. Since Internet is a computer network widely used around the world, it is greatly suitable for constructing wide-region and large-scale distributed monitoring systems, as its infrastructure can be used to achieve automated acquiring, transferring, storing, announcing and utilizing of status data in wide region with lower construction and maintenance costs of network. It can be predicted that distributed monitoring system may become a very important Internet application in the near future.There are some common problems about key technologies in constructing distributed monitoring system, though both the types of monitored objects and the ways of monitoring terminals connecting to Internet are various. It is necessary to research the key technologies and resolve the common problems, which will help to shorten the development period and enhance the implementation efficiency of distributed monitoring system, so as to accelerate their applications in multiple domains. There were multiple key technologies including data acquisition technology, network communication technology and system integration technology researched, and a series of technology obstacles eliminated for constructing distributed monitoring system in Internet environment, with the support of"Construction of a Recording and Monitoring System for Working Status of Large Scientific Instruments", a project funded by the National Basic Condition Platform for Science and Technology of China (No. 2004DKA10010, 2005DKA10103). On this basis, a distributed monitoring system for working status of large scientific instruments was designed and developed, and it has been put into actual use in several universities and institutes all over country, with online monitoring of many large scientific instruments implemented.(1) Research on data acquisition method to detect computer programData acquisition technology, which provides raw data for distributed monitoring system, plays a most important role in the whole system. It is a primary problem how to implement the data acquisition of various parameters of monitored objects, and the traditional data acquisition method for distributed monitoring system is to detect characteristic physical signals of monitored objects. Since there are many local monitoring systems whose cores are computer systems, a new data acquisition method for distributed monitoring system to detect computer program was proposed, which indirectly acquires various parameters of monitored objects through detecting computers and their software of local monitoring systems rather than characteristic physical signals of monitored objects. The new method makes full use of the data acquisition capability of local monitoring systems, and it is also convenient to implement. Take scientific instruments as an example, in order to acquire their status data, there were multiple ways involved in the new method to detect the control software. These ways are event detection of Windows OS based on mouse and keyboard hook, feature detection of human-machine interface based on pattern recognition, log file detection of the control software based on schema matching and data flow detection of communication interface. Because the new method obtains working parameters of scientific instruments from their controller computers instead of the instruments themselves, the risk of detecting characteristic physical signals from precision scientific instruments was escaped. To be especially indicated, in the feature detection of human-machine interface based on pattern recognition, Mirror Driver was adopted for screen capture and an improved Sequential Similarity Detection Algorithm (SSDA) was applied for screen recognition, so its speed was improved effectively. (2) Research on communication approach of distributed monitoring systemIt is an important problem how monitoring terminals communicate with upper-layer information system of distributed monitoring system. There are three work patterns that are center-controlled pattern, independent running pattern and offline pattern in distributed monitoring system, and the communication approach between monitoring terminal and upper-layer information system lies on work patterns and network environment of distributed monitoring system. Three main communication approaches of distributed monitoring system, including monitoring terminal as a server, monitoring terminal as a client, and monitoring terminal as both a server and a client, were discussed and analyzed, and it was concluded that all of them have difficult to resolve the following problem: Since IP addresses in IPv4 are limited in number, monitoring terminals usually use private IP addresses, which are reserved by RFC 1918 for use on private networks and not reachable across Internet, in this situation, whichever existing communication approach was adopted, it is required that port mapping should be configured on NAT (Network Address Translation) gateway for center-controlled pattern. This special requirement for network environment has been an obstacle to implement distributed monitoring system due to inconvenience to change network environment in some condition. So Instant Messaging (IM) used for near-real-time text-based chatting originally was introduced to provide a new communication mechanism for distributed monitoring system, in which although monitoring terminal runs as a client, the upper-layer information system can obtain its presence rapidly through the presence service and communicate with it actively. The IM-based communication mechanism supports all work patterns of distributed monitoring system without network environment such as usage of private IP addresses limited, and is also convenient for identity authentication and centralized management of monitoring terminals. It is the foundation of designing a full wide-applicable communication solution for distributed monitoring system in Internet environment.(3) Research on XMPP-based communication protocol of distributed monitoring systemIn order to ensure the safety and reliability of communication between monitoring terminals and upper-layer information system, it is necessary that a robust communication protocol be designed for on-line monitoring of distributed monitoring system. Since it is a low-efficient method to design a proprietary communication protocol from scratch, Extensible Messaging and Presence Protocol (XMPP) that is an open standard in the IM domain was introduced and extended, and an XMPP-based communication protocol for on-line monitoring of distributed monitoring system was proposed, which implements the IM-based communication mechanism mentioned above with a design and implementation solution provided in details. The communication protocol has high extensibility and security, as its function is carried out based on Extensible Markup Language (XML) with Transport Layer Security (TLS) used for encryption and Simple Authentication and Security Layer (SASL) used for authentication. In the communication protocol, server side was implemented using plug-ins of Openfire that is open source XMPP server software, and client side was implemented with C programming language for different platforms including low-speed embedded device. Its test and application shows that it is wide-applicable and suitable for constructing various distributed monitoring system in wide-band or narrow-band TCP/IP network.(4) Research on integration policy of information system in distributed monitoring systemThe design and development of information system in distributed monitoring system can be accomplished through system integration, including the integration of internal information system and external information system, also the integration of individual components in internal information system, which is strongly influenced by system heterogeneity and requirement changing. What architecture is adopted for information system will decide its difficulty and efficiency to implement, so architecture design of information system in distributed monitoring system is not an ignorable problem. The general model of information system in distributed monitoring system was abstracted, and then the integration policies of information system that using client-server architecture and distributed objects architecture in distributed monitoring system were discussed and analyzed. However, both integration policies are incapable of rapid integration of information system in heterogeneous environment, because of their close coupling of all parts and shortcoming in opening and flexibility. So, a service-oriented open architecture of information system for distributed monitoring system was proposed with Service-Oriented Architecture (SOA) applied, and it was employed to provide core support for service-oriented integration policy of information system in distributed monitoring system. This open architecture summarizes the common features and reduces the coupling level of information system, and it is excellent in opening and flexibility with web services platform chosen to support it. The information system of distributed monitoring system can be designed using the open architecture, so as to support the integration of individual components in internal information system, also the integration of internal information system and external information system. Then the influence of system heterogeneity and requirement changing will be weakened, the difficulty of development will be reduced, and the efficiency of implementation will be enhanced as well.(5) Design and implementation of distributed monitoring system for working status of large scientific instrumentsIt is necessary that a distributed monitoring system for working status of large scientific instruments should be constructed to automatically record their running information, which can be used for their networked management and application evaluation so as to advance their opening and sharing. As large scientific instruments are usually located in different universities and institutes all over country, all research productions about key technologies including data acquisition technology, network communication technology and system integration technology of distributed monitoring system gained above were utilized to design and implement a full remote near-real-time distributed online monitoring system for working status of large scientific instruments in Internet environment, whose design, development and deployment solution were provided in details. Now the distributed monitoring system has been put into trial running in several universities and institutes of different districts all over country, and successfully resolves the problem that the true usage status of large scientific instruments could not be automatically recorded in their networked management, with the feasibility and practicality of research productions about key technologies mentioned above shown. The distributed monitoring system holds not only important practical value for scientific instruments but also referenced value for other distributed monitoring system in multiple domains.The research productions of this paper can be used to rapidly build a flexible platform of distributed monitoring system in Internet environment, with which there is no need to spend too much consideration on some public parts, and moreover, developers of multiple domains can pay more attention to data acquisition and business logic of various monitored objects. Then the efficiency of implementing distributed monitoring system will be enhanced.
|
PDF Full Text Request