Computer network structure
The following networks are distinguished by the size of the covered territory:
• small local or domestic (radius from several meters to tens of meters);
• local (radius from hundreds of meters to several tens of kilometers);
• distributed (radius from hundreds to several thousand kilometers);
• global (covering several or all continents of the globe).
A distributed or local network with a single owner or single owner is called corporate .
The structure of local networks can be different:
1. Linear bus - all computers are connected to the same communication line (Figure 10.1), if there is damage in which the network stops working. Currently, the line bus is rarely used, mainly with a small number of computers. The disadvantage is low security. At the input of the network adapter or network card of each computer, whether it is switched on or not, participates in the network exchange or not, all information transmitted over the network comes.
Fig. 10.1. Line Bar
2. The ring connects all computers to each other in sequence (Figure 10.2). If there is any damage, the network either ceases to work entirely, or the falls apart to individual operating sectors. Currently, the ring network structure is rarely used, because, like the line bus, it does not provide proper security. Any of the enabled computers can listen all information transmitted over the network.
3. A fully-knit network (Figure 10.3) is built on the principle of connecting computers each with each potential customer. With the simplicity of the structure, and therefore the apparent ease of management, a fully connected network requires a large number of communication lines and a significant number of network ports in each computer. Network rendering -
Fig. 10.2. Ring
Fig. 10.3. A fully-knit network
is cumbersome and expensive, as a result of which it is not often used. Fully-connected networks are used on very busy information crossings global networks where one server is running "on the verge of collapse". Connecting several closely located servers to a full-mesh network significantly increases the throughput at this information crossroad.
4. Distributed star (Figure 10.4). In the center there is a passive (unmanaged software) switching device - a hub, which excludes the transmission of transmitted information "in the wrong hands", i.e. on a computer that does not participate at the moment in the information exchange.
5. Star is the most common structure of local networks at the moment. At the center of the structure is an active (program-controlled) switching device - the server (Figure 10.5).
Fig. 10.4. Distributed Star
Fig. 10.3. Star
Basic elements of the local network
Server is a computer, "maintenance management" on the network with the help of their devices, programs and data, providing services to other computers (workstations of the network, clients) for communication, receiving, sending and processing information, and also shared resources.
Strictly speaking, a server is a program that is installed on a computer for servicing collaboration on the network of other computers. But since through a similar computer leaks a lot of information, its hardware is trying to make it more powerful. Increase the amount of operational and disk memory, use faster processors, install either several conventional network caches, or network devices: switches (switches), routers (routers). For this reason, the server is also referred to as a computer, maintenance manager online. Typically, the server runs around the clock to ensure uninterrupted access to information posted on it.
Workstation, or host (host) is a computer connected to the network and having its own address in the network. This can be either a server or a client computer.
Client is a computer on the local network where the user starts the application programs and accesses the server from the server to communicate with other computers and access to network resources (files, programs and devices). Unlike the server, although the client is physically connected to the network, at certain points in time it can be logically (programmatically) disconnected from it. Another difference - the client at different times can be both permanent and different (changing in each session of the network) address.
In addition to the main actors (clients, servers), there are many other service devices on the network that the user does not directly work with, but on which the speed of the network and its security depend greatly. Therefore, the user must know which devices can be installed on their own to strengthen the security of their computer or network segment, if they are not present on the site: the user's computer is the provider's server.
Repeater (repeater) is a device on the network that allows you to restore the amplitude and power of the transmitted signal, which are reduced due to the presence of losses in communication lines.
Concentrator (concentrator), or hub (hub), is a multi-input (or multiport) repeater that allows multiple computers to be serviced at once.
Bridge (bridge) - software or hardware for converting information when exchanging information between similar networks or their parts (logical segments).
Switch , or switch (switch, switching hub) is a communication device in which parallel independent processing of information arriving at different ports (inputs) is possible. This distinguishes it from the bridge, where information coming from different ports is processed one by one (sequentially).Router (router) - a set of software and hardware that provide the network with the transfer to destination (on a given route) data packets and share information flows of individual parts of the network from each other.
Gateway (gateway) is a device for connecting different types of networks, working with different network software and using different protocols.
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