28.10.2020

Ethernet switches

The Ethernet switch is a large networking device. In order to better understand the design and operation of Ethernet switches, it is useful to understand the basics of the technology for organizing cable network systems.

Repeaters

In the early 80s, Ethernet networks were organized on the basis of bus topology using segments based on coaxial cable up to 500 meters in length. The increase in the size of the networks set the task of overcoming the 500-meter barrier. To solve this problem, repeaters were used:

The repeater simply copies (forwards) all Ethernet packets from one segment to all others connected to it. The main objective of the repeater is to restore electrical signals to transmit them to other segments. Due to amplification and restoration of the shape of electrical signals by the repeater, it becomes possible to expand networks based on coaxial cable and increase the total number of network users

Bridges and Routers

When using repeaters, the maximum length of the network is 2500 meters. To overcome this limitation, other devices called bridges are required. Bridges have many differences from repeaters. Repeaters transmit all packets, and bridges only those that are needed. If the packet does not need to be transferred to another segment, it is filtered. For bridges, there are numerous algorithms (rules) for transmitting and filtering packets; the minimum requirement is filtering packets at the recipient address.

Another important difference between bridges and repeaters is that the segments connected to the repeater form one shared medium, and the segments connected to each port of the bridge form their own environment with a bandwidth of 10 Mbps. When using a bridge, users of one segment share a strip, and users of different segments use independent Environments. Therefore, the bridge provides advantages both in terms of network expansion and providing a larger band for each user.

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