In The Short-wave Channel. The E-mail Applications And Improvements

The development of communication technology has shown that one of the most competitive factors of the communication system is the low cost and the concise implementation. There is the congenital shortage that HF (High Frequency) communication's ionosphere channel is time-variant and dispersive. However, its concise implementation and its low cost to communicate all over the world, even in abominable conditions, makes other communication schemes cannot substitute it. That is why HF communication can still be widely used and be developed continuously.In 80's, American Department of Defense constituted the standard of forming network by HF. Now looked like, it belonged to the 2G HF network. It offered credible, vigorous and finely compatible link automatic establishment technology. In the mid of 90's, because of the development of the technology and the request of the application, people requested that HF network could transmit more data. Traditional HF communication services (such as voice, message, point-to-point data transmission etc.) cannot fit the needs of the war. Moreover, they requested as little frame consuming as possible. To adapt to the requirement of the change, the 3G HF network was coming. The appearance of the 3G HF network made HF communication which was mainly used to point-to-point transmit started to turn to study the HF net's capability of forming network and intercommunication with other various of networks. As the Internet applications coming into the modern digital war, it becomes a hot aspect that how to append the Internet services to HF network, and how to make the HF network become a part of the Internet, and how to implement seamless link between them. Additionally, the world has paid more attention to E-mail. It has been widely used in Internet because of its storage and transmission mechanism, non-real time transmission mode, low requirement of bandwidth and channel quality, and easy to be implemented on HF channel.This thesis discusses two aspects about how to build an E-mail system in HF channel: the transferring scheme and protocol used for communication. It also analyzes the limitation of TCP protocol used in HF channel directly and the necessity of the use of ARQ protocol. Based on the analysis above, this thesis realizes an E-mail system in HF channel. And then, considering the particularity of HF channel, this thesis puts forward an amendment to the HF E-mail system, namely, E-mail transmission protocols HMTP (HF Mail Transfer Protocol) and HF-POP3 faced to HF net. And the thesis proves its feasibility in a real system. Finally, the thesis comprehensively tests each of the schemes, and analyses the results, which provides authentic reference to the further study.