Switched telecommunication systems: terminals, transmission links and exchanges
G. Smol, M. P. R. Hamer, M. T. Hills · 2023
The transmission channel between two terminals which send and receive analogue signals can be described, first, in terms of its bandwidth, and secondly, in terms of the impairments of the message signals which it causes. In designing each element of a switched system, it is necessary to relate the various impairments which they introduce into the transmission channel to the effect these have on the user. A large number of experiments must therefore be carried out in order to establish empirical relationships between each type of impairment and user dissatisfaction. This is particularly difficult when a combination of two or more impairments has to be considered. The first element of any telecommunication system, whether switched or non-switched, is the terminal. In some cases, however, the terminal may not be a fixed one which can be regarded as a part of the system; the user may be able to connect any one of a number of terminals to the system.