What is circuit switching?

All currently existingtelecommunication networks to provide the required functions can use two types of communication - switching channels and (or) packets. What is it and how do they differ from each other?

Let's start, perhaps, with how networks work withcircuit switching. They appeared earlier their counterparts with switched packages, therefore, which is not surprising, they are easier to implement. A vivid example of a network that uses circuit switching is a telephone line. Obviously, in order for two subscribers to start communication, it is necessary to establish a connection between them. The initiating subscriber dials a number that, in fact, is a command to the equipment of the telephone exchange (ATS) located between them, to properly connect the two lines - from the initiator and from the respondent (we take an example when subscribers are served by one station). Earlier for this, mechanical probes were used on the simplest position sensors, then, with the advent of digital solutions, the implementation changed, although the principle remained the same. Channel switching provides subscribers with an independent line that remains attached to them until the end of the communication session. Advantages are obvious: high reliability, absence of necessity of transfer of control packages. However, this method of connecting with increasing the number of subscribers becomes too wasteful, since the number of channels is physically limited. Even an attempt to solve this problem by applying seals is only a temporary measure determined by an intermediate solution. In addition, switching channels has one significant drawback - the communication line is busy all the time, even if there is no information exchange between subscribers. For example, during a telephone conversation, you can put a handset next to the device and go about their business - the channel will remain reserved for them until a signal is received to sever the connection.

That's why afterwards to replaceThe switching method of the channels was the method of packet switching. The principle of its operation assumes the encoding and splitting of the transmitted data stream into a number of separate packets that are transmitted along the common communication line to the receiver and are combined therein into the original stream. In order to understand the differences between the two methods, we can use the analogy with the transport line: in the case of channel switching, the line is represented by a railway track, and the data stream is a train consisting of a plurality of wagons. It is understandable that delays are extremely rare on the way, and reliability is one of the highest. At the same time, several trains can not move simultaneously along this track. But the lines with packet switching are a high-speed highway with multi-band traffic. The transported cargo (transmitted packets) is divided into several vehicles that, maneuvering in the flow of other modes of transport, reach the destination where the initial design is assembled. In this example, a road is a communication channel, and machines are data packets. They quietly coexist on the same road, almost without interfering with the movements of each other. Exceptions are congestion, traffic lights and emergency situations (these are delays). Even if a machine has not arrived at the recipient, a copy of it on request can be sent again. The total amount of information transmitted per unit of time for packet switching is significantly higher than in the case of channels.

In general, switching is switching something,change of states. In networked technology, it forms a route for data transfer. The peculiarity lies in the way it is organized. Switching should not be confused with routing, whose task is to find the optimal route.