The principle of topology is that some properties of geometric figures will remain unchanged under continuous deformation. Topology studies some properties that geometric figures or spaces can remain unchanged after constantly changing their shapes. It only considers the positional relationship between objects, without considering their shapes and sizes. In topology, important topological properties include connectivity and compactness. Topology does not discuss the concept of congruence between two graphs, but the concept of topological equivalence.

Topological classification:

1. bus topology. The topology of the bus is that all devices in the network are directly connected to the public bus through corresponding hardware interfaces, and the nodes communicate through broadcasting, so that the information sent by one node can be "monitored" by other nodes on the bus. Advantages: simple structure, easy wiring, high reliability and easy expansion, and it is a common topology structure of LAN.

2. Star topology. Each node is connected with the central node through a separate communication line. Advantages: simple structure, easy realization, easy management, easy monitoring and troubleshooting of connection points. Disadvantages: the central node is the reliable bottleneck of the whole network, and the failure of the central node will lead to network paralysis.

3. Ring topology. Each node forms a closed loop through communication lines, and the data in the loop can only be transmitted in one direction. Advantages: simple structure, easy realization, suitable for using optical fiber, long transmission distance and definite transmission delay. Disadvantages: Every node in the ring network becomes the bottleneck of network reliability, and any node failure will cause network paralysis, and fault diagnosis is also difficult.

4. Tree topology. It is a hierarchical structure, and nodes are connected according to levels. Information exchange is mainly carried out between upper and lower nodes, and data exchange is generally not carried out between adjacent nodes or nodes at the same level. Advantages: simple connection, convenient maintenance, and suitable for the application requirements of collecting information. Disadvantages: low ability to enjoy resources and low reliability. The failure of any workstation or link will affect the operation of the whole network.

5. Mesh topology. Also known as irregular structure, the connections between nodes are arbitrary and irregular. Advantages: The system is highly reliable and easy to expand, but the structure is complex. Each node connects multiple points, and routing algorithm and flow control method must be adopted. At present, WAN basically adopts mesh topology.

Above content reference: Baidu Encyclopedia-Topology