In a wide-area distributed environment such as the Internet, users exchange information by using a common application protocol. Such an application layer protocol forms the basis of information communications, and once it is widely spread, it is difficult to replace the protocol by a new improved or extended protocol. In order to enhance the spreading use of the protocol, the following conditions are necessary: (1) Both the server and clients should be able to use the new protocol. (2) It should be possible to handle the new protocol without modifying the existing client application. (3) The user should be able to handle the new protocol transparently. This paper presents a method in which the above three conditions are satisfied by using a mobile code technique in order to facilitate the spread of a new application layer protocol. In the proposed method, the mobile code that converts the existing protocol to the new protocol is distributed transparently to clients, and the spreading use of the new protocol is realized. By making the mobile code operate within the restrictions of a sandbox, the security of the client computer against defects of the mobile code is improved. The proposed method is independent of the architecture of the distributed mobile code. In this study, the mobile code is implemented in i386 native code.
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