What are the common network structures? What are their characteristics?

1. Common network topologies mainly include star structure, ring structure, bus structure, distributed structure, tree structure, mesh structure and honeycomb structure.

2. Features

① Star structure. Star structure is the oldest connection method, and the telephone that people use every day belongs to this structure. The general network environment is designed as a star topology. Star network is one of the widely used and preferred network topology designs.

Star structure means that all workstations are connected into a network in a star way. The network has a central node, and other nodes (workstations, servers) are directly connected to the central node. This structure takes the central node as the center, so it is also called centralized network.

Star topology is convenient for centralized control, because communication between end users must pass through the central station. Because of this feature, it also brings the advantages of easy maintenance and safety. When the end-user equipment stops due to a fault, the communication between other end-users will not be affected. At the same time, the network delay time of star topology is short and the system reliability is high.

② Ring structure. Ring structure is widely used in LAN. The transmission medium in this structure goes from one end user to another end user until all end users are connected in a ring. Data is transmitted in one direction between nodes in the loop, and information is transmitted from one node to another. This structure obviously eliminates the dependence of end users on the central system when communicating.

The characteristics of ring structure are: each end user is connected with two adjacent end users, so there is a point-to-point link, but it always runs in one direction, so it is called upstream end user and downstream end user; The information flow in the network is fixed, and there is only one path between two nodes, thus simplifying the control of path selection. All nodes in the loop are bootstrap control, and the control software is simple; Because the information source is transmitted in series through all nodes in the loop, when there are too many nodes in the loop, it will inevitably affect the information transmission rate and prolong the response time of the network. The cycle is closed and inconvenient to expand; Low reliability, if one node fails, the whole network will be paralyzed; It is difficult to maintain and locate the faults of branch nodes.

③ Bus type. The information transmitted on the bus is usually transmitted serially in the form of baseband. The hardware of the network interface board on each node has the functions of receiving and sending, and the receiver is responsible for receiving the serial information on the bus and converting it into parallel information and sending it to the PC workstation. The transmitter converts parallel information into serial information and then broadcasts it to the bus. When the destination address of information sent on the bus coincides with the interface address of a node, the receiver of the node receives the information. Because the nodes are directly connected by cables, the cable length required in the bus topology is the smallest, but the bus has only a certain load capacity, so the bus length is limited, and a bus can only connect a certain number of nodes.

④ Distributed. Distributed network is a form of network that connects computers distributed in different places through lines. The network with distributed structure has the following characteristics: due to decentralized control, even if a part of the whole network fails, it will not affect the operation of the whole network, so it has high reliability; The shortest path algorithm is used to select the path in the network, which has less online delay time and high transmission rate, but the control is complicated. Data links can be established directly between nodes, and the information flow is the shortest; It is convenient for the resources within the whole network to enjoy. Disadvantages are long connecting cable and high cost; The network management software is complex; Packet switching, path selection and flow direction control are complex; General LAN does not adopt this structure.

⑤ Tree structure is a hierarchical centralized control network. Compared with star structure, its total length of communication lines is shorter, its cost is lower, its nodes are easy to expand, and it is more convenient to find paths. However, the failure of any node or its connecting line will affect the system except the leaf node and its connecting line.

⑥ Mesh topology. Mesh topology mainly means that nodes are connected with each other through transmission lines, and each node is connected with at least two other nodes. Mesh topology has high reliability, complex structure, high implementation cost, difficult management and maintenance, and is not commonly used in local area networks.

Connect multiple subnets or networks to form a mesh topology. In a subnet, hubs and repeaters connect multiple devices, while bridges, routers and gateways connect subnets. According to different network hardware, there are three main mesh topologies:

Mesh network: In a large area, when a large network is connected by radio communication links, mesh network is the best topology. Connecting with the router through the router allows the network to choose the fastest path to transmit data, as shown in Figure 5-4.

Backbone network: Different subnets or LANs are connected by bridges and routers to form a single bus or ring topology. This network usually uses optical fiber as the backbone.

Star connection network: The network is connected by some devices called super hubs. Due to the characteristics of star structure, any fault in the network can be easily found and repaired.

⑦ Cellular topology is a common structure in WLAN. It is characterized by point-to-point and multipoint transmission through wireless transmission media (microwave, satellite, infrared, etc.). ), and it is a wireless network, suitable for city network, campus network and enterprise network.

The term topology is borrowed from geometry. Network topology is the shape of the network or the physical connectivity of the network. Network topology refers to the physical layout of various devices interconnected by transmission media, that is, how computers and other devices in the network are connected. The topology diagram shows the network configuration and connections of network servers and workstations. There are many kinds of network topologies, including star structure, ring structure, bus structure, distributed structure, tree structure, mesh structure, honeycomb structure and so on.