Computer network

A computer network is a combination of different technical, primarily independent electronic systems (in particular computers, but also sensors, actuators, agents and other radio components), which enables the individual systems to communicate with each other. The aim here is, for example, the shared use of resources such as network printers, servers, files and databases. Also important is the possibility of central administration of network devices, network users, their authorizations and data. Direct communication between network users (chat, VoIP telephony, etc.) is also of particular importance today.

Communication takes place via various protocols that can be structured with the ISO/OSI model. Although in practice no computer network completely represents the ISO/OSI model, it is of decisive importance for the understanding of computer networks, since larger and more complex structures are formed from small basic structures by linking. In the process, higher (more complex) protocol layers access the functionalities of simpler protocol layers below them.

An important principle here is that so-called user data can be passed to most protocol layers for transport. The protocol layer adds further data to these user data (whose content it largely ignores) at the front and sometimes at the back, which are important for the handling of the transport by the protocol layer. However, there are also exceptions to this, since some protocols are not intended to transport external user data, but function exclusively as independent information systems for certain tasks.

The most commonly known network structure is the Internet, and the best-known protocols are the TCP (Transmission Control Protocol) and the IP (Internet Protocol), but a number of other protocols also play important roles in the Internet. The Internet itself is not a homogeneous network, but consists of a large number of subnetworks, some of which are designed quite differently, which only have the upper protocol layers in common and handle the transmission of user data at the lower protocol layers very differently in some cases.

Within a computer network, the central computer or main computer is the computer - usually a mainframe computer - that provides the other connected computers (such as workstations or terminals) or the programs run on them with data, services, system programs, application programs and the like.

Topologies

Topology refers to the way in which the various components involved (i.e. mostly computers) in the network are connected by physical or logical paths. In order to integrate several computers in a computer network, good planning is required, which is simplified by the division of the topology. In this way, computer networks are formed in which there are connections and nodes that can be used to reach every other area of the network, if necessary via several intermediate points.

There are a number of basic stereotypes that rarely occur in practice in this clear form. In the star topology, there is a central distribution point that can control everything if necessary and without which nothing works. This topology is actually only used in very small networks, for example home networks or LAN parties. A connection of several star topologies at their concentration points is also called an extended star topology. Tree topology uses a similar approach, but staggered hierarchically. The "top" computer has control over all the others, the power shrinks the lower you sit in the tree. In the ring topology, each computer has a position in a ring and is only connected to its neighbors. As a result, the failure of one computer cripples the computer network. In bus topology, all the participating computers access a medium that is shared and used by all, which can cause collisions on it. The meshed network is a form in which each computer is connected to multiple neighbors and in which redundant paths exist, so that even if one line fails, the network still remains connected through another line. Cell topology plays a special role in wireless networks with their special access characteristics.

In practice, mixed forms of these stereotypes almost always occur, and there are still a number of designations for certain special forms. For example, the spontaneous, self-organized networking of any devices is referred to as a smart network or smart grid.

Diagram: Network Topology

Organizational coverage (network architecture)

This criterion is often used because it seems less complicated than other properties of networks. In practice, however, this distinction has only limited significance.

Local networks

• Body Area Network (BAN)
• Wireless Body Area Network (WBAN)
• Personal Area Network (PAN)
• Wireless Personal Area Network (WPAN) as a term
• Local Area Network (LAN)
• Wireless LAN (WLAN) as a term

Non-local networks

• Metropolitan Area Network (MAN)
• Wide Area Network (WAN)
• Global Area Network (GAN)
• Virtual Private Network (VPN)
• Storage Area Network (SAN)