Learn in the textbookNetwork Classification and the Physical Foundation of Wired Connections
DefinitionA communication line (通信回線) is the communication route used to send and receive data between devices or sites in separate locations.
ExplanationMany lines, such as telephone and fiber-optic lines, are offered as services by carriers, though some are laid and managed by the company itself. A method in which one pair of users holds the route for the entire exchange is circuit switching (回線交換方式), while one that splits data into small units called packets (パケット) so many users can share the line is packet switching (パケット交換方式). When usage piles up all at once and traffic stalls because it exceeds what the line can handle, the state is called congestion (輻輳).
AnalogyCircuit switching is like a chartered bus, and packet switching like a regular route bus. On a charter you are sure of a seat but many seats go empty, while a route bus fills its seats without waste.