Originally all telephone exchanges were analog, and communication between them (and also between them and subscribers) was carried out by means of analog connecting lines. However growth of load of communication lines connected with an intensification of information streams and expansion of a circle of the problems assigned to telecommunication resulted in need of a choice: or to increase cable capacity through increase in number of communication lines (that conducted to significant increase in cost telephone an usla, or to look for essentially new decisions. As a result there were digital communication lines - Digital Trunk Interface (DTI) which allowed to increase number of channels at preservation or even reduction of number of connecting wires.
All these services are integrated into the ISDN technology and are available to any subscriber of ISDN. Also there are many additional services which are processed at the level of ISDN of the equipment and do not demand support from station.
The fourth distinctive feature of new technology is ability of ISDN stations to carry out automatic routing of connections that is especially important in cases when between stations there are some alternative ways of connection and it is necessary to choose the most optimum.
Thanks to that BRI contains two various channels of data, two subscribers - or for two telephone conversations, or for telephone conversation and data transmission, including the Internet at the same time can use the ISDN line. In general it is possible to connect to the ISDN line to 8 various devices, each of which will get own identification number.
Progress does not stand still. Now it is Videotelefoniya. All of us already much about it heard. But now it not somewhere in the wild West, and at us in Rostov and is quite real. Interestingly as with arrival of a video telephony to change the crown phrase "Hallo"?
Two THAT types — external and built-in are issued. External are executed in the form of the separate device with the power unit. They function according to one program put in it focused on granting the interface with ISDN to this or that type of the terminal equipment (for example, are available THAT for connection of the terminals working under the X.25 or 24 protocol or on the a/b interface).
However and ISDN have the problems which are expressed both in insufficient standardization and in need of replacement of the software of each automatic telephone exchange at introduction of new services ISS. It runs into money and demands existence from the operator of a network of enormous intuition because in this case the step is a failure aside. Time of "life" of the switching equipment - some tens years therefore in case of rendering new service it is inexpedient to replace its every time but also not to do it it is impossible: after all the steady growth of requirements to increase in number of functions which have to be supported by a network is available. Thus not only the structure of networks becomes complicated, but also there are more labor-consuming management processes and operation.
Let's say there are two remote offices. What to unite them enough, in everyone them them to draw an ISDN line and to get ISDN/Ethernet a router. Exchange speed between networks will be 128 kbps. Besides, you can use in parallel with information exchange ISDN phone, without division of networks. But with use of ISDN phone, in operating time of the last, exchange speed between networks will fall to 64 kbps, but only for the period of its work!
Having defined in general scope of ISDN and having considered its main opportunities, we will pass to consideration of technological features of one of the most perspective telecommunication systems of the present now.
Present as it is convenient to chief to check work of the subordinates on a videotelephone. Or as it will be pleasant to relatives who did not see each other long ago and live in the different world's ends, it is not simple to talk, but also to see each other. And can do it and the first step to individual television.