What are the elements of an information transmission system?

A complete information system consists of three parts: source, channel and destination. Any information has a source and a destination. Among the three elements, source, channel and destination, source and destination can be interchanged. When Party A and Party B make a phone call, the information sent by Party A is the source and the information received by Party B is the destination; When Party B gives feedback according to the information sent by Party A, Party B becomes a source, and Party A receives feedback from Party B, and then becomes a destination, and so on. However, as a bridge between the source and the destination, the channel is relatively unchanged. Information can circulate, but the content of information must be reflected in a certain form, which is the "signal". In other words, information is transmitted through certain signals, and signals play the role of information carriers. When an information source sends out information, it is usually represented by some kind of signal, such as electric signal and radio communication. And optical signals such as wireless optical communication (atmospheric laser communication) and wired optical communication (optical fiber communication). The same piece of information can be expressed by language (such as transmitting information by telephone), characters (collectively referred to as letters, numbers and symbols), images (such as transmitting information by telegraph or fax machine), and can also be converted into computer codes. In addition, the information sent by the source can be compressed and transmitted quickly in a short time, or compressed into a small space and stored first.