The data switching technology usually used in telephone communication networks is line switching technology; line switching technology is also called circuit switching technology. It is a direct switching method that can provide a pair of devices that need to communicate. A temporary dedicated channel provides a dedicated transmission channel, which is both a physical channel and a logical channel.
The operating environment of this tutorial: Windows 10 system, DELL G3 computer.
The data exchange technology usually used in telephone communication networks is line switching technology
Line switching technology is also called circuit switching technology. Circuit switching is a direct switching method. It provides a temporary dedicated channel between a pair of devices (stations) that need to communicate, that is, it provides a dedicated transmission channel, which can be both a physical channel and a logical channel (when used) or frequency division multiplexing technology). This channel is completed by the internal circuit of the node through appropriate selection and connection of the transmission paths between nodes. It is a link composed of multiple nodes and multiple transmission paths between nodes.
A brief introduction to the three stages:
The switching method widely used in public telephone networks is circuit switching. Communication via circuit switching includes three stages:
(1) Circuit establishment:
(2) Data transmission:
(3) Circuit removal:
Circuit establishment
Complete the required node-by-node connection (connection) process in the switching network through the source site request to establish a transmission channel from the source site to the destination site. For example: To complete communication between A and D, the total process is for A to apply to node 4. Usually, the link from A to 4 is a dedicated line, and node 4 is in the three transmission paths 4-1, 4-5, and 4-7. Select one as a path, such as 4-5, and establish a connection between the A-4 path and the 4-5 path within node 4, and so on, and then establish a connection between the 4-5 and 5-3 paths within node 5. , and finally the connection between the 5-3 path and the 3-D path is established internally in node 3, and the final transmission channel between A-D is A-4-5-3-D.
Data transmission
The signal can be transmitted from A to D through the established link, usually full-duplex transmission.
Circuit teardown
After completing the transmission of data or signals, the source station or destination station proposes to terminate the communication, and each node will tear down the circuit accordingly. The corresponding connection of the circuit releases the node and channel resources occupied by the original circuit.
Summary of technical features:
(1) The call establishment takes a long time and there is call loss. During the circuit establishment phase, it takes a period of time to establish a dedicated path between two stations. This period of time is called the call setup time. During the circuit establishment process, the establishment fails due to reasons such as busy switching network. For the switching network, part of the established circuit must be removed, and the user needs to hang up and redial. This is called call loss.
(2) After the circuit is connected, what is provided to the user is a "transparent channel", that is, the switching network does not impose restrictions on the encoding method, information format, and transmission control program of user information, but for both communicating parties , the sending and receiving speed, encoding method, information format, transmission control, etc. of both parties must be consistent to complete the communication.
(3) Once the circuit is established, data is transmitted at a fixed data rate. There is no other delay except the propagation delay through the transmission link. The delay at each node is negligible. It is suitable for Real-time high-volume continuous data transfer.
(4) Line (channel) utilization is low. The circuit is established and data is transmitted until the communication link is removed. The channel is dedicated. Coupled with the communication establishment time, removal time and call loss, its utilization rate is low.
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