GLOSSARY

Analogue signals - these are continuous sliding signals, having wave diagram (for example, voice vibrations). Bounded spectral composition of that signals let transmit them by telephone channels contrary to discrete signals, having impulse view and, therefore, a very broad (theoretically unlimited) spectrum.

Videoconferencing - is the service rendered by electrical communication and computer networks providers and supplying audio and video information exchange in the real-time operation mode between geographically remote members of group.

Fiber Optical Communication Lines - are an optical or polymeric medium used for data transmission. Transmitted light waves are radiated by laser type source. Fiber Optical cables provide a high secrecy of communication having a broad bandwidth and occupy little place. They may be considered as physical medium for all land-based communication systems in the future.

Dedicated line - is nonswitched channel between 2 or more network terminals, directly connecting the subscribers. Dedicated lines are always available for sole unlimited using for fixed rent.

Circuit switching - data transmission method when a temporary communication channel is set up between terminals. The switched channel is established only for communication time and after that the switching break signal is sent. The example of the realization of the network with channels switching may serve the telephone communication system.

Packet switching - is a network technology, transmitting data in the form of packets. Besides data each packet contains information about destination address and bits for errors control. The packets may be transferred by different (individual) network routs via X.25 or Frame Relay and collected together in the destination point.

Concentrator (hub) - Each device of local network is most often linked to the concentrator usually placed in mounting cabinet. Concentrator is a device assigned for transmission of data via several incoming channels into less number of outgoing. Additionally, a lot of concentrators may keep received data till outgoing will be free and ready to receive it.

Corporative network - is a network providing the work and interaction of corporation employees independently of company's dimension, number and remoteness of branch offices, therefore, the functioning of the company as a whole, using modern equipment and software and also different communication sources. The network as a rule involves different types of computers starting with desktop and ending with mainframes, system and applied software, network adapters, concentrators, switches and routers, cable system etc. besides corporative network, in case of need, is linked to different external networks, for example, global network Internet. And also in case of need it is possible to link the network to different finance and information systems.

Local area network (LAN) - is usually placed at the same building and belongs to the separate organization. Local network lets combine computers, printers, scanners, signal systems (fire alarm, intruder alarm) etc. Besides in this network it is possible to share the disk space, files, and corporative databases, using fax-servers, modem pools and different expensive devices.

Router - is a device providing the traffic between 2 logically different (having net addresses) local networks. It is function at 3-rd (net) level of OSI model and responsible for choice of rout of packet transmission between hubs. The rout is chosen on a basis of routing protocols containing information about network topology and routing algorithms. Routers are also used in the Internet main network.

Multiplexing - is the technology that permits to part a communication line between several devices. Owning to multiplexing there is no need of allocating the phone line for each computer. Multiplexers T-1 part the line on 24 channels each of that may use separate device.

Fiber Optical Cable - is a version of data transmission medium on the base of glass (unlike the traditional cooper cables). Its dominant feature is absence of electrical signals that predetermines full protectability from electromagnetic influence of any descent. It is used for organization of data transmission on higher speeds in comparison with speed reachable for cable based on cooper twisted-pair cable.

Bandwidth - is a measure of transmission channel's information capacity. Capacity of the analog telephone line is measured in hertz and is a difference between maximal and minimal frequency achieved in channel. Bandwidth of digital channel during data transmission is measured in bits per second.

Signalling - is a data transmission process between 2 parts of network for control, routing and phone call supporting.

Terminal equipment (data terminal equipment, DTE) - is device transmitting and/or receiving data: multiplexers, office PBX, switches, and personal computers.

Digital signal - is a signal, for example voice, presented by discrete level order (for example 0 and 1) and closely defies to distortion during its transmission. Digital signal is more stable to the noise and using it permits to raise the communication quality.

ADSL (Asymmetric Digital Subscriber Line) - It is arranged by asymmetric scheme. Data transmission rate "up" (from client) and "down" (to client) is unequal. This line is also known as "full-rate" ADSL.

BRI (basic rate interface) - basic interface of ISDN, based on 2 channels of B class by 64 kbit/sec and 1 signal channel (D class) for 16 kbit/sec.

Centrex - is a central exchange. As distinct from office PBX, the switching equipment of that is at the territory of enterprise or organization, Centrex is an equipment of central ATS and belongs to local telephone company.

Frame Relay - It is a public access network usually used for connecting some local networks. Data transmission is realized by telephone lines aver that each local network is connected with Frame Relay network. Frame Relay services require fewer expenses for operation, equipment and maintaining in comparison with traditional access to communication services if there is more than 4 carried presence points.

ISDN (integrated services digital network) - It is a digital network with integration of services and product of analog telephone network evolution provides transmission of information in digital form over all connection and is access by standardized set of user interfaces.

PRI (primary rate interface) - It is consist of 29 channels for voice transmission, video materials and data (B class) and 1 signal channel (D channel)/ Each of 30 PRI channels has a 64 kbit/sec capacity.

SDH (synchronous digital hierarchy) - It is a standard of data transmission by optical medium, realized through hierarchic consistent file of multiplexers. The main technology of information transmission in transport fiber-optical networks from 50 Mbit/s to 2,4 Gbit/s.

VPN (Virtual Private Network) - They are networks permit to reach functional capability of private network without laying the physically dedicated line between offices of the organization. In this case each office or store just connected with provider's network.