28.10.2020

Switch switch

The team of the electronics design center Promwad returns to Habr after the winter holidays with new articles on the development of firmware and new devices for serial production. Today we will share our experience in the topic of network technologies.

The average home network, as well as the network of a small enterprise, is no longer just two or three computers connected via the first Chinese switch that came across. Together with an increase in the volume of content (databases, streaming audio / video, etc.) and an increase in the number of devices (VoIP devices, servers, NASs, IP cameras, and in home networks – TVs and the other “Internet of things” ) the amount of data transmitted through the network infrastructure is growing. Data streams need to be divided among themselves, while not forgetting the prioritization of traffic: for example, it is desirable to start up VoIP traffic with a higher priority than IPTV, and IPTV, in turn, than torrents. Therefore, it is not surprising that over time, even small local networks become more complex, and the port capacity of single switches becomes insufficient … To increase the port capacity of large network nodes, as well as to increase the overall network bandwidth, they often resort to the construction of so-called stacks – combining switches into hierarchical structures depending on the streams of transmitted data.

The most “classical” architecture for building networks is a tree, as shown in the figure:

At the same time, traffic from node A to node D passes through a chain of upstream switches, which imposes additional performance requirements – the throughput of each next (upstream) tree node must be higher than the previous one.

In order to relieve the main nodes of the network, additional connections between switches are most often introduced. For example, the “core” of the network is often organized as a ring of switches, as shown in the diagram below:

If the good old Ethernet is used, then in order to avoid overflow of the ring with broadcast traffic, they use the Spanning Tree Protocol, which puts one of the links between the ring switches in an inactive state. This allows you to provide an alternative traffic path in the event of a break in the central ring at any point. If any of the protocols specially designed for “rings” is used, for example, FDDI or Token Ring, then the ring does not break, and traffic is transmitted along the ring with the most uniform loading of the switches included in the ring.

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