Briefly describe the definition of communication system and the composition of computer communication network.

Communication system is the general name of the technical system used to complete the information transmission process. Modern communication system is mainly realized by the propagation of electromagnetic waves in free space or the transmission mechanism in guiding media. The former is called wireless communication system and the latter is called wired communication system.

Communication system consists of three parts: source, sink and channel. Among them, we usually call the sender of data the source and the receiver of data the sink. The source and destination are usually computers or other data terminal equipment.

In order to realize effective data transmission between the source and the sink, a transmission signal must be established between the source and the sink.

The number of physical channels, this channel is called physical channel, referred to as channel.