The English name of the hub is "Hub". "Hub" means "center". The main function of the hub is to regenerate, shape and amplify the received signal to expand the transmission distance of the network, and at the same time concentrate all nodes on the node centered on it. It works on the first layer of the OSI (Open Systems Interconnection Reference Model) reference model, the "physical layer". Like transmission media such as network cards and network cables, hubs are basic devices in the local area network and use CSMA/CD (a detection protocol) access method.

The hub is a pure hardware network bottom device, and basically does not have the "smart memory" ability and "learning" ability similar to the switch. It also does not have the MAC address table that the switch has, so when it sends data, it is not targeted, but is sent by broadcasting. That is to say, when it wants to send data to a node, it does not directly send the data to the destination node, but sends the data packet to all nodes connected to the hub, as shown in the figure.

This way of broadcasting data has the following disadvantages:

(1) User data packets are sent to all nodes, which is likely to bring insecurity factors in data communication, and some people with ulterior motives can easily intercept other people's data packets illegally;

(2) Since all data packets are sent to all nodes at the same time, coupled with the bandwidth sharing method described above, it is more likely to cause network traffic jams and reduce network execution efficiency.

(3) Non-duplex transmission, low network communication efficiency. At the same time of the hub, each port can only carry out data communication in one direction, but cannot carry out two-way duplex transmission like a switch. The network execution efficiency is low and cannot meet the needs of large-scale network communication.

Because of this, although the hub technology is constantly improving, it is essentially adding some switch (SWITCH) technology to develop today's stackable hubs with stacking technology, and some hubs also have smart switch functions. It can be said that the hub products have transitioned to the switch technology in technology, and have certain intelligence and data exchange capabilities. However, as the price of switches continues to drop, the only price advantage is no longer obvious, and the market for hubs is getting smaller and smaller, and is on the verge of being eliminated. Nevertheless, the hub is economically attractive for families or small businesses, especially suitable for use in a network of several machines at home or as a branch network for small and medium-sized companies.