The development history of communications

2020-08-06 18:10:10Zongheng Intelligent Control 3

The development history of communications

(1) The earliest communication: beacon tower, beacon; letter: electronic communication (telegraph, telephone, network signal)
(2) The two most important aspects of communication are information representation and analysis methods and information transmission methods.
(3) Both communicating parties need to agree on the representation method and analysis method of the information in advance, otherwise the information cannot be transmitted effectively. (4) The transmission method of the I signal refers to how the encoded communication information is transmitted on the transmission medium. process.
Summary: The communication process is actually divided into 3 steps: first, the sender encodes the effective information according to the information encoding method (programmed into a signal form that can be transmitted on the communication line), and then the encoded information is transmitted on the transmission medium. Transported to the receiver; finally, the receiver decodes the encoded information after receiving it, and obtains valid information that can be understood after decoding.

Synchronous and asynchronous communication

(1) The difference between synchronization and asynchronousness; First of all, there are concepts of synchronization and asynchronousness in many places. Simply put, the sender and the receiver work according to the same clock beat, which is called synchronization. The sender and the receiver do not have a unified clock beat. And each works according to its own rhythm, which is called asynchronous work.
(2) In synchronous communication, both communicating parties work according to the same two beats, so the cooperation is very good: _ Generally, the sender needs to send information to the receiver and send a clock signal at the same time, and the receiver arranges its own time according to the clock signal given to it by the sender. Rhythm. Synchronous communication is used when the frequency of information exchange between the communicating parties is fixed, or when communication occurs frequently.
(3) Asynchronous communication is also called asynchronous notification. When the frequency of communication between the two parties is not fixed (sometimes sending and receiving once every 3ms, sometimes sending and receiving once every 3 days), it is not suitable to use synchronous communication, but asynchronous communication is suitable. In asynchronous communication, the receiver does not have to care about the sender all the time. When the sender needs to send information, he will first give the receiver a starting signal for the beginning of the message. After receiving the starting signal, the receiver thinks that what follows is valid information. It will start to pay attention to receiving information until it receives the end sign from the sender.