Research And Implementation Of The Reliable Message Handing System Based On X.400 Protocol

With the accelerated development of network technology, email is becoming one of the most important tools for message transfer, but the primary problem is that the e-mail system, widely used on Internet, is unreliable in message transfer. Though the unreliability for common communication is acceptable, in some province such as military affairs and finance which need the requirement of high reliability, the unreliability is unacceptable.Today, the widely accepted mail transfer protocols are SMTP(Simple Mail Transfer Protocol) and X.400 protocol. Comparing with SMTP, X.400 supports more reliable controls, involving delivery report and receipt report. Because of this reliability, X.400 protocol is usually used in some provinces which advance high reliable requirement.Based on the deep analysis of X.400 series of protocol, aiming at the requirement of application, this essay designs and implement a message handing system based on X.400, which can guarantee the reliable transfer between users. And the content can be generalized as followed aspects:1. The research studies the X.400 series of protocol deeply, especially the MHS(Message Handing System) including its framework and function of each portion.2. The research promotes a new MTA(Message Transfer Agent) system frame. According to function this frame divides MTA into two services: Message Service and Reliable Transfer Service. The first service takes charge of the communication with the UA(User Agent), the second one transfers the messages to the remote service.3. The research designs a multilevel reliable message transfer protocol which can support the requirement for reliability of various applications. Using this protocol, users can trace the message sending status when they send a message.4. The research promotes some mechanisms to implementing the reliability and efficiency of message transmission between complex, bad, low speed network channel. There are three mechanisms for reliability such as dynamic variable-length pachetization,broken-point continuingly-transferring and some Qos.5. The research implement a message handing system based on X.400 protocol, which guaranteeing the reliable transmission of messages.The key point of the essay is 3 and 4 point. The former is used on Message Service, ensuring the multilevel, reliable message communication between services, the latter is used on Reliable Transfer Service, guaranteeing the reliable message transmission over different network.