Research On Application-Level Protocol For Data Transfer In G/S Mode

With the development of spatial information technology, more and more network application services need based on spatial information. In this condition, G/S mode which provide a new solution for organization, management, display and description of massive, diverse, heterogeneous spatial information. Through the aggregation of services in client by "request– aggregate - serve", G/S mode could convert the data stored in distributed spatial data servers to various application services, and aggregate these services dynamically in client. G/S mode could provide users with a variety of spatial information based network application services, such as navigation, digital tourism, intelligent transportation and emergency relief.In G/S mode, data could be classified to service data and system data. Service data, which is transferred from servers to users, is used for providing services of G/S mode. System data, which is much smaller than spatial data, is used in communications of servers. How to solve the network transfer tasks of these two types of data simply and efficiently is the key to complete the "request– aggregate - serve" process in G/S mode. However, due to the lack of unified norms and standards, in current G/S mode research and practice, appeared different methods of data transmission, they are unable to completely solve the transmission problems arise from the difference between various data, though.In view of this situation, this paper has researched the data types and characteristics of G/S mode, and studied existing application-level data transfer protocol, sorted out the data transfer issues need to be resolved in G/S mode, and achieved the following results:(1) Designs an application-level data transfer protocol for G/S mode, which is called "Hyper Geographic Transfer Protocol"(HGTP), and could provide reliable data transmission for G/S mode.(2) Proposes a controllable transmission method for raster data, stratify data without any increase in the amount of data, improving the transmission efficiency of raster data.(3) Presents a lightweight data transmission security control method, implements the security control of communications within spatial information servers, provides some security for servers.