Network Active Components

In the early days of local networks, connected devices such as PCs shared an Ethernet cable (coax) over which all data packet were transferred. Since the length of the cables was limited, cables were connected with bridges. These bridges simply repeated the signal they received on one side to the cable on the other side.

In the course of development, the bridges developed into switches that connect each device individually via twisted pair (TP) cables. However, the basic working principle has not changed: A switch forwards data packets, which it receives at one port, to many other ports. 

A modern switch learns the MAC addresses of sender and receiver and remembers via which port the corresponding devices are connected to it. This enables it to forward data packets in a targeted manner after short time. The latest switches perform these tasks so quickly that data packets from different devices are transmitted simultaneously and there is virtually no delay. 

Many of the switches available today have also additional features. This enables them for example to automatically identify the transmission and reception line pairs of a connected cable and adjust to them. This function is described as Auto MDI/MDI-X. Another function is auto-negotiation, with which the switch can negotiate the maximum transmission bandwidth (Ethernet, Fast or Gigabit Ethernet) and also the duplex mode with each connected device. Many switches can also be configured from a connected PC via a web interface. This allows the administrator for example to prioritize certain packets (QoS – Quality of Service) or filter addresses. 

A special highlight are PoW switches (power over Ethernet) which as PSE (Power Supply Equipment) can conduct not only data but also the supply of power for the connected device via a twisted pair cable.