| With the deterioration of the environment, the government hasconcerned with environment protection. Environment monitoring is animportant measure to protect environment. To improve the level ofenvironment monitoring in our country, many information systems ofenvironment monitoring have been developed. The Systems have upgradedthe level of environment monitoring to some extent, but there are also manydeficiencies. Doing some application research in this field can remedy thedeficiencies of the systems and improve the level of environment monitoringin our country further, so it is very valuable.The task team has designed the system architecture of software andhardware based on the current situation of environment monitoring in ourcountry and started from environment monitoring instruments, designedvarious network connection equipments derived from the currentcommunication conditions, designed software founded on customs'requirements.The software system uses the distributed architecture. The task teamcompared and analyzed two distributed architectures, which are J2EEand .NET, so that suitable architecture would be chosen. Considering thecustoms'requirements and the development strength, .NET XML WEBSERVICE architecture was adopted. The most advantage of the architectureis that the communication protocol of the architecture is http, which caneasily pass the firewall.After the construction of the distributed architecture, the most importanttask is to find the method that can implement the remote data collection andremote instrument monitoring. Remote communication architecture wascreated, which needed correlative hardware and network condition support.The architecture is composed of control terminal, server, data transfer andinstrument. Here, in order to depict expressly, the data transfer and theinstrument will not be distinguished which are called instrument.The software in server is the backbone of the whole remotecommunication and all information will be transmitted by it. The socketcommunication mechanism is the basis of the software. The programlanguage is JAVA. Multithreading and synchronization mechanism in JAVAare also introduced.The Server builds a socket listening port firstly, then the port receivesdifferent connection requests from different clients (they are instruments andcontrol terminals). When various clients send connection requests, the requestmessage is different also. The server can parse the different message, andthen create corresponding listening thread resting on client type marked bythe message. Each listening thread has a unique ID, which is very vital. Allthe listening threads can be divided into two types, which are control terminalthreads and instrument threads. The two kind threads make up of two threadqueues whose members corresponding to various clients. While some controlterminals send message to certain instrument, the message will be receivedby the corresponding thread in the control terminal thread queue and beparsed. Then according to instrument ID in the parsed message, the messagewill be transmitted to the corresponding thread in the instrument thread queue.The process above implements the communications among control terminals,server and instruments. In remote communications, the information interaction among the threeends is referred, so the up-level communication protocols must be needed.The communication protocols refer to the information encapsulation andinformation parsing rules, which are used when control terminalscommunicate with instruments by server and different from bottom networkcommunication protocols commonly. Establishment of the communicationprotocols that the system adopts makes reference to the principle of IPpackage in TCP/IP protocol. The communication protocols divided the stringin the transfers into several segments and the segments denote message type,message receiver, message sender and message body respectively. In theprocess of the message transfers, the message will be parsed andencapsulated, then reach the destination and feedback message return. Theprotocols can be used conveniently in application, but they have the fault thatcan't be extended easily. Maybe it is a good choice that the message isformatted by XML. In this system, there are two kind control terminals, one of them isdesktop computer, and the other is a handset terminal. The software indesktop computer is similar to the common software, but the one in handsetterminal are special. The kinds of the handset terminals are various, some ofthem base on CDMA network, other of them base on GPRS network. Thehandset terminals supported by this system base on GPRS network, whichcan connect with Internet and support J2ME. Aiming at these mobile phones,the JAVA program that can run in them has been developed and released onthe simulator. A JAVA program that supports NOKIA6600 has beendeveloped in the system development period, by which the operator canmonitor remote instruments conveniently. On the other hand, other simulatorcan also compile the source code, and then the program can run in the mobilephone with the corresponding type. By this way, the problem of thecompatibility of the different type mobile phone has been resolved. |
