Lektsiya №15

Computer networks

The Computer network (the angel. Computer NetWork, from net - a network and work - a functioning) - a collection computer united by means of channel relationship and facilities to switchings in united system for messaging and access of the users to programme, technical, information and organizing resource to network.

The Computer network present as collection of the elements (the computer and network equipment) and connecting their branches (the channel relationship). The Branch to network - a way, connecting two adjacent elements. Distinguish the elements final - located at the end only one branch, intermediate - located on the end more then one branch, and adjacent - such elements united, at least once, one way, not contain no other elements. The Computers can unite in network by miscellaneous way.
Logical and physical ways of the join computer, cables and the other component, as a whole forming network, is identified her(its) topology. The Topology characterizes the characteristic of the networks, not hanging from their sizes. Herewith is not taken into account power and principle of the functioning these object, their types, lengths channel though when designing these factors very important.
The Main requirements presented to telecommunication networks Power - time to reactions, reception capacity and delay of the transmission.
Expandability - a possibility of the light accompaniment separate element to network (the users, computer, applications, service).
Masshtabiruemosti - a possibility наращиваемости network without lost capacity.
Reliability, safety to information and protection from distortion - duplication separate element, creation mines and others Safety of the transmission to information - special programme and hardware.
The Components hardware and software of the networks Workstation - a computer, connected to network and under governing the local operating system.
The Servers to network - execute the functions of distribution control network resource and granting the different sort of the service services.
The Communication elements - a modems, repeaters, commutators (the bridges), routers, floodgates and others Means of communication - a coaxial cable, twisted pair, оптоволоконный cable, telephone.
Software - for decision of the tasks of the processing in-sytuctures, realization of the planning and organizations of the multiaccess to information resource of the network, dynamic distribution these resource.