Further development of the idea of integration is to bring together an extensive telephone network to data networks in a structure called the Digital Network Integrated Services (ISDN), in which data services and speech are provided simultaneously. Stimulating factor in the transition to ISDN is a low cost of data transmission over digital telephone network and the continued cost of service of voice to the already existing networks.
Giving the most common response in accordance with the definition of the International Consultative Committee for Telephony and Telegraphy (CCITT, now the International Telecommunication Union - ITU), one can say that ISDN (Integrated Services Digital Network - ISDN) - a network that grew out of a digital telephone network and providing digital connectivity from end to end (end-to-end) to support a wide range of services, including audio and other services, intended for users with a limited set of standard interfaces such as multi-user network.
As the name implies, the main aim is the integration of ISDN services to support them (video, audio, voice and data) required four separate networks. Video transmission is carried over coaxial lines, audio - for balanced lines, radio networks, for voice use copper twisted pair, and for services associated with the transfer of data requires coaxial or balanced cables. This variety of equipment is expensive to install and difficult to use. In the ISDN is different.
ISDN provides the ability to send voice, video and audio information data on one network with a unified cable equipment with incomparable with the previous network quality. This network is characterized by a variety of additional features such as automatic control of the width provided by the channel and establish a connection in the delivery of services.
One of the main reasons for not being able to provide full services listed above on the public telephone network - its analog nature. Using the analog channels is particularly unsuitable for applications intended for data transfer. In the analog network modulation process is used to convert digital data stream coming from the computer and consists of zeros and ones in a sequence of analog tones or pulses. On the receiving side of a process called demodulation, converts this sequence back to digital. The process of modulation-demodulation is very inefficient for the organization of the above services due to noise interference of the echo lines of low quality and limited bandwidth communication channel.
Networks require high-speed channels. Basic ISDN channel has a speed of 64 kbit / s, so that ISDN is an excellent tool for connecting, for example, local area networks. Just as computer networks, ISDN itself is digital, but it is not limited to buildings, urban area or city. It could be regional, national and even global. Velocity parameters and the digital nature of ISDN allows you to connect two remote devices for thousands of miles as easily as if they belonged to the same LAN and placed in adjacent rooms.
The first development in the area of ISDN started in 1976, and today we are witnessing the widespread introduction of ISDN in developed countries. Since 1988, however, the main efforts of the developers were focused on the development of the concept of a network that will be more revolutionary than ISDN. The new network was called Broadband ISDN (W-ISDN) and was originally conceived to address the fact that it is the successor to ISDN and be able to maintain its service, namely:
Ensure the transmission of voice and nonverbal information in a single network;
provide a non-switched, so dial-up connections, and providing for the possibility of circuit and packet;
ensure the possibility of dial-up connections for digital channels at 64 kbps.
On the other hand, W-ISDN will have a much greater capacity than ISDN. ITU-R characterizes the life of ISDN as a service requiring high-speed channels. For this simplified formulation, however, is highly complex network development plan and a set of services that will have far greater impact on the economy and social sphere of the world than ISDN. With the advent of W-ISDN will be possible services requiring data rates of tens, hundreds or thousands of times greater than the speed permissible in the ISDN. These services include handling graphics, HDTV, Ethernet, etc. This type of service are known as broadband services. They require high-speed channels on all sections of the network, as well as the respective switches.
Thus, the basis W-ISDN are high-speed and fast switching, providing a wide range of speeds and traffic parameters. All this becomes possible in the case of fiber optic cable and the so-called asynchronous transfer mode (ATM). The decision to use ATM for R-ISDN is quite remarkable and suggests that R-ISDN will be packet-oriented network, if we talk in terms of its interfaces and internal switching. Thus, R-ISDN, which began its development from a telephone switching network channels into a packet-switched network with the expansion of broadband services.
W-ISDN originated from narrowband ISDN or ISDN, but in fact only uses some of its ideas. In fact, W-ISDN ISDN is very different from the architecture and implementation, as the latter, although it is intended to implement digital transmission, but is designed to use existing cable systems, mostly copper, we inherited from the analog telephone networks. At the same time, W-ISDN as a transmission medium uses mostly fiber and relies on high-speed networking technology to provide users with a wide range of services - from narrowband to broadband. The following topics will be discussed in greater detail broadband service, and asynchronous transfer mode.
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