Research Of Remote Sharing Technology For Workstations' Screen Image Of Large Scientific Instruments

At present, our country is facing the problem that overall resource of large scientific instrument is insufficient. Under this background, the realization of large scientific instrument remote network experiment has great significance. A number of large scientific instruments'experimental process is controlled by workstations, whose screen image may embody the experimental process.Therefore, the remote sharing technology for workstation screen image of large scientific instruments is the key technology of the network experiment. The realization of the technology provides possibilities of the participation and learning remote experiments for researchers and students.Overseas, the beginning of the control software including remote screen image sharing function was early, already mature, widely applied to commerce, family, national defense, astronautics, etc. But the beginning of domestic research is later, which has a tremendous development space. This kind of software all has remote control functions in rich, such as remote shutdown/root, activation/ termination of remote program process, long-distance disk management, modification of registry, etc. Owing to these functions can threaten the security of workstations, which are not applied to the remote network experiment for large scientific instruments. In view of the characteristics of workstations'screen image and the requests of design, this study has made research mainly about the screen image sharing technology of large scientific instrument.On the basis of studying RFB (Remote Frame Buffer) protocol, this study simplifies the protocol to take it as the communication protocol of this design, With the thought of modularizing design, it has designed and realized the C/S (client /server) scheme both server and client terminal software on the platform of Visual C++6.0, on the basis of studying technology in Hook, network communication, multi-thread, compression, image acquisition and so on.1. Simplification of the RFB protocol According to the actual application requires, on the basis of studying in RFB protocol, the simplified RFB protocol is taken as the communication protocol of this design.2. Server terminal software⑴Studying Socket network communication technology and developing network communication moduleSocket is a basic unit of network communication supporting TCP/IP protocol. In the design, the basic communication function of Socket communication is implemented, and the transmission for screen image with a mass of data is specially optimized. In addition, the Nagle algorithm initiated by default is closed, solving a problem of data adhesion.⑵Studying Hook technology and designing module for hotspot capturing of the screen based on Hook technology and polling scheme Owing to a mass of screen image data, if the entire screen image is transmitted directly, the efficiency of the network transmission will be reduced, influencing the real-time performance of screen image sharing. On the basis of making a further research in Hook technology, using which both the message causing the screen changing and the message of mouse keyboard could be monitored, to implement the module of hotspot capturing of screen and reduce the amount of transmission image data. But Hook technology cannot ensure to capture all the screen changes, obviously the console window, IE scrolling window and so on. Therefore, the hotspot capturing of screen in polling scheme is designed to compensate it in the way of Hook, realizing hotspot capturing of screen comprehensively. In addition, rectangular areas capturing screen changes are disposed, removing the overlap image regions to reduce the transmission of the image transmission data.⑶Researching the acquisition technology of Windows OS screen image based on the GDI and developing the module of screen image and mouse cursor.The format of the image intercepted by GDI function BitBlt is DDB, whose display relying on the system hardware, neither through disk nor through network transformed to other computers to achieve sharing. Therefore, we need to translate DDB bitmap file format into other image format to sharing with other computers via network. DIB (Device Independent Bitmap) is an external image format, which overcomes the shortcomings of the DDB, used to share the screen image from one mainframe to another through network or other medium. In this design, DIB image format is applied to share the screen image. DIB section is used to store the data of DIB bitmap, which can enhance the transform speed from DDB to DIB. DIB section, a memory storing DIB data, is a storage space accessed by both application program and device driver program. Kinds of GDI operations can be executed in this memory to access it directly, that will enhance the speed of DIB bitmap processing and display.According to the cursor handler,the position and the shape of cursor can be obtained to acquire the mouse cursor, drawing the cursor into the intercepted image.⑷Researching multi-thread technology and image compression technology, using the open-source Ominthread and Minilzo-2.02 provided by open-source organization, and implementing the multi-thread design and LZO image compression algorithm3. Client terminal software"Thin client protocol"is used in this design, the main job of which is concentrated on the server terminal, and the client terminal's is relatively simple.The main purpose of the client terminal is to receive image data transmitted from server terminal by the rule of protocol flow, using LZO code mode to decompress the image data and displaying DDB format image transmitted from DIB format image on the client terminal. In order to enhance the transmitting speed from DIB format to DDB format, DIB Section is used for storing the image data in this paper.In this paper, through the research of screen-sharing technology of image, a remote sharing system of screen image for large scientific instrument has been designed and implemented, solving a key technology for the experimentation of large scientific instrument network. At the same time, this technology could also be used in the network classroom, remote education and other fields. Through experimental tests, the real-time performance of screen image sharing is good in the LAN, and the screen is also fluent, but the performance is not good in the campus network and education network, needed to improve in the future.