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Key positions






THE ACTIVE NETWORK EQUIPMENT.

BRIDGES-ROUTERS

Purpose of work

Studying of principles of the bridge and the router operation, the network screen and acquisition of practical skills of main modes operation and maintenance customization.

Key positions

Practically in all cases, whether it be one computer or set of computers united in a local area network, exists necessity of an output for external wide-area networks for call to Internet resources and an informational exchange with other local area networks. Such active network equipment as modems, bridges and routers, network screens is with that end in view used.

Modems, as is known, are intended for conversion of digital signals in analogue with their subsequent transmission on telecommunication lines, and also for restoring of an initial digital signal at reception. As there is a set of the various environments through which data exchange is carried out, created and many types of modems. Depending on coordination of data transfer modems can be divided to divide on two big categories:

• Synchronous

• Asynchronous

Asynchronous modems can lose to 25 % of time for transmission and reception negotiation. Synchronous are effective use accessible link speed and provide faster communications than asynchronous modems.

The remote bridge ( Remote bridge). It is the bridge intended for data transfer of one local segment through a wide-area network in other local segment. It builds the table of MAC-ADDRESSES on the basis of the traffic passing through it and on the basis of it make solution - to transfer frames in a remote segment or not. If usual bridges almost do not find today applications the remote it is applied often enough. They do not need to be configurated and this property appears very useful at remote offices where there is no qualified serving staff.

The bridge ( Bridge). Works at channel level. Is a transmission medium of frames on the basis of the physical address between two segments using, as a rule, identical protocols of physical and channel levels. Thus, bridges provide the extension of a network, which does not demand program modifications on the workstations working in local segments. All servers working in segments, use unique addresses at interaction and are not obliged to distinguish obviously the server of an own segment and the server of other segments. Bridges care of it. The bridge should know, what addresses of channel level (MAC-ADDRESS) belong to each segment to define what frames to skip, and what to return in the segment. For this purpose it has a circuit of operation with addresses. If some segments are linked by several bridges each bridge should have as well the table of paths of passing through bridges. For operation support in conditions when frames stay faster, than they can be transferred, the bridge should have sufficient size of the buffer.

The router (router) unlike the switch supports protocols not only physical and channel levels, but also network. Network layer protocols provide collection of the information on topology of connections between logical networks and construction of tables of routing with paths to all logical networks known to a router. (Methods of definition of paths, optimal by the set criteria are considered in following section). On the basis of router’s routing tables fulfils transmission of packages from one network in another and can make of solution for choice the most rational path of an information transfer in difficult topology of link (topology with closed loops).

Has some physical interfaces, including, various network technologies, and also can provide economic access to territorial networks as isolates the local traffic more effectively. If the router is capable to support some protocols of network layer, it is named as a multyprotocol router.

The circle of functional tasks of a router includes also buffering, filtering and a fragmentation of packages. Therefore it is a typical computer with one or even several processors and with the difficult software of real time. As each package is handled by a router separately, its productivity considerably loses to productivity of the switch. There can be a bottleneck, braking a traffic passing if it is installed at kernel level.

The router role can fulfil the server computer in the event that the network layer of its operating system supports transmission of packages. Universal OS of Unix set or Windows include the program unit providing customisation of a mode " router".

 

Association of two remote local area networks by means of two modems Zyxel Prestige 128L.


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