Computer network

a computer network is a union of different technical, primarily independent electronic systems (in particular computers, in addition, sensors, actuators, radio-technological components etc.), which makes communication possible of the individual systems among themselves.

Communication is made by different minutes,by means of the ISO/OSI model to be structured can. Although in practice no computer network illustrates the ISO/OSI model completely, it is formed of crucial importance for the understanding of computer networks, there here from small fundamental structures by linkage, larger and more complex structuresbecome. Higher (more complex) protocol layers access functionalities of simpler underlying protocol layers.

An important principle thereby is that one can hand data (Payload) in each case to most protocol layers over (using) to transport. The protocol layer adds to these utilizable data (of themContents of it to a large extent ignore) in front and partly in the back further data on, which are important by the protocol layer for the completion of transport. However there are also of it exceptions, there some minutes not in addition meant is stranger utilizable data to be transported, butexclusively as independent information systems for certain tasks function.

The most well-known lattice structure is that Internet and most well-known minutes is the TCP - and the IP - minutes, however a number of further minutes and that play important roles also in the InternetInternet is not a homogeneous net separates is developed from a multiplicity of partly quite differently conceived subnetworks, which have only the upper protocol layers together and which utilizable data communication on the lower protocol layers to handle partly very different.

Computer networks can among other things on the basisthe following criteria to be classified.

  • Organizational cover
  • transmission path/transmission technology

table of contents

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topologies

diagram: Net topology

this is a characteristic which can be understood relatively easily for the basic understanding is important. By the topology one understands the kind like thosedifferent components involved (thus mostly computers) in the net by physical or logical routings are connected. Theoretically one could connect each computer directly with every other computer involved. This is however not practicable in practice. Therefore one forms nets into those connections and knots gives it over which one if necessary. over several intermediate points of each range of the net to every other range of the net to come can.

There is a set of basicstereotyped, so in this clear form however rarelyarise in practice. With the star topology there is a central point of distribution, that if necessary. everything to control can, but functions without the nothing. With the tree topology one uses a similar beginning which one however hierarchically graduates. In the ring topology everyone hasComputer a position in a ring and is connected only with its neighbours. The meshed net is a practical form in each computer is connected with several neighbours and redundant ways exists, so that even in case of failure a line thatNet still remains connected by another line. In a bus all computers involved access together and all medium used of, whereby it can come to collisions on it. The cell topology plays with radio nets with its special access characteristicsa special role.

In practice combinations this stereotyped one arise and it nearly always give still another set of names for certain special forms.

Closer details for this see under the keyword topology of nets.

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organizational cover

of thisCriterion it often used there appears less complicated than other characteristics of nets. In practice this distinction has however only limited meaning.

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transmission path

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wire-bound one of nets

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Ethernet

the most common technology with wire-bound nets is the Ethernet, which meets one particularly in local firm nets and home nets. It is line and today in developments 10BaseT, 100-Base-Tx and 1000-Base-Tx is used. The number designates in each casethe theoretical maximum transmission rate of 10, 100 or 1000 Mbit per second and T says out that it a gedrilltes copper cable concerns (twisted pair). Depending upon speed a cable of the appropriate quality is necessary, the CAT [number]one calls. For 100 Mbit e.g. is this. CAT5 to use with 1000 Mbit CAT5e, CAT5+ or CAT6.

In former times the Ethernetvariante 10Base2 with coaxial cables was common, which became extinct to a large extent however since the year 2000. Agitates nevertheless from thisTime the name Ethernet, which suggests that one over kind “ether” function. Background was that many computers a common Ethernet strand divided and it could come so also to disturbances when simultaneous use (so-called collisions). The “access procedure” calls itselfCSMA/CD (carrier scythe multiple ACCESS/Collision Detection), whereby each computer listens only whether the line (carrier) is free and if, then simply sends. It has pitch gives it nevertheless a collision, because still another computer does the same.This collision recognized (Collsion Detection) and both to try it at a coincidental time later again.

Besides each computer, which used the Ethernetstrang, had knows when it was meant. In addition the so-called MAC (Media Access Control) was introduced layer, thosethe simultaneous access on the together used medium regulated. Each computer involved got its own clear MAC address and it gave oneself procedures like all computers with the occurrence of a collision to behavior had. In practice the Ethernet/MAC hasMinutes the advantage that it with small data traffic very fast and simply functions, since everyone can loose-transmit immediately. However arise to more and more collisions in the together genutzen net section with higher data traffic, which let the data traffic break sometime completely togethercan. In practice such Ethernet of nets functioned therefore only with small data traffic well. With high data traffic large delays could develop and theoretically could it for a computer pass that it could coincidentally at all never send collision-free something.

With arisingthe cousin T variants and Switchen became again actually unimportant these MAC procedures, since now again each computer had its own exclusive network area, which was controlled by Switche, however remained the MAC layer. There are no more collision problems nevertheless today with Switchen,whereby the lines can be used more efficiently, however it can come still to back-up and overloading at the Switchen.

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token ring

another way of the access supervision went that to token loop - net, the 2005 particularly for netswith special quality requirements one uses. The advantage of token loop - nets it is that each computer can surely send something after at the latest a certain time. In addition a so-called token (too German pledge coin) in form of a small information package is handed. Who tokensmay if one while has utilizable data send, then and passes that hears tokens on. The sequence in that is passed on it is exactly fixed and circular, whereby one gets tokens again and again.Token loop - nets are often in such a way developed,the fact that each computer is directly connected with its two neighbours in the ring in each case and either token passes these on or hands or passes themselves on information over either kept, depending on for whom she is intended. There is also oneVariant the token ring of over Ethernet calls itself. All computers in a together used Ethernet are connected, but continue to themselves give there in each case a token reihum (token Passing), whereby collisions are avoided and the line are better used.The complicated at this virtual ring is that firstonce must be clarified which computers to exist and which order those in the virtual ring to take. Besides one must recognize if new computers come or existing in the ring disappear.

Those are really importantCharacteristics of token loop - nets in sensitive nets, in which it is important, precisely to know like for a long time maximally lasts it, until a message can be sent. This leaves itself easily on the basis the number of computers, thus at the length of theRing determine. Such nets are used for example in the automotive engineering and financial industry for critical systems.


Some further net types are:

further access procedure:

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wireless ones of nets

common techniques with wireless nets are mobile phones


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infrastructure nets

spontaneous Adhoc nets are

furthest (see MANET)

  • WLANs of the type 802.11 in the Ad-hoc-mode. In this mode the devices of the net without additional infrastructure communicate.
  • with very small range the devices in direct environment connect, so-called. Wireless personnel AREA network (WPAN)
  • the standard Bluetooth (see also Toothing)
  • One uses lattice structures for sensor nets, current
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] linguistic view of net and

network the English net traditionally in the fishery. Outside of this range one speaks however of network. In German network stands traditionally onlyfor the mesh work of a Fischer net. Outside of the fishery only net ( electricity mains becomes, not - work; Telephone network) uses. This argumentation computer network a wrong translation from the English and computer network is following and/or. Computer net the correct term (see also * Bastian crimp: BULB FISH ABC: Net/network. In: Mirror-on-line).

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literature

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see also

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Web on the left of

Commons: Computer network - pictures, videos and/or audio files
 

  > German to English > de.wikipedia.org (Machine translated into English)