In the IT field, network equipment usually refers to hubs, switches, routers and so on. In a large network topology, there are multiple layers of network devices, such as switches divided into access layer, aggregation layer, and core layer. Considering network stability and reliability, core layer switches will be redundant not standby. Industrial network equipment is also composed of these hardware components, with the addition of special equipment such as industrial gateways and industrial control computers. The main difference lies in two aspects. Firstly, industrial network equipment has additional stringent requirements for adapting to the on-site environment and durability; Secondly, ordinary network devices such as switches sometimes cannot meet the rea-time requirements of industrial ethernet for data forwarding and require dedicated industrial switches.
Hubs, switches, and routers work at the physical layer, data link layer, and network layer, respectively. The simplest network connection we encounter is two computers interconnected through two network cards. Generally, unshielded twisted pair cables are used between the two network cards. Due to the gradual attenuation of signals during transmission, twisted pair cables can cause signal distortion. Therefore, while ensuring signal quality, the maximum transmission distance of twisted pair cables is usually limited to 100 meters. When the distance between two computers exceeds 100 meters, in order to unsure the quality of communication between the two computers, a relay is installed between these two computers. The function of the relay is to sort out the already attenuated incomplete signal, generate a complete signal again, and continue transmission. Repeaters and amplifiers are similar in that they both function as signal amplifiers, with the difference being that amplifiers amplify analog signals, while repeaters amplify digital signals.
A repeater is the predecessor of a regular hub, which is actually a multi-port repeater. Hubs generally have Ethernet (RJ45) interfaces with different numbers of configurations such as 4,8,16,24,32, etc. Through these interfaces, hubs can achieve signal “relay” for the corresponding number of computers. Due to its intermediate position in the network, a hub is also known as a hub. The working principle of a hub is simple. Assuming a 4-port hub is connected to 4 hosts, the hub is located at the center of the network and forwards signals through the hub. The 4 hosts can communicate with each other. The specific process is as follows: if host 1 wants to send a message to host 4, when the network card of host 1 sends the information to the hub through twisted pair, the hub cannot directly send the information to host 4. It will broadcast the message and send it to all ports. After receiving the broadcast message, the hosts on all ports will check the message. If they find that the message is intended for themselves, they will receive it, otherwise they will ignore it. Hubs simply assume the role of the physical layer-message carriers.
Post time: Mar-26-2025