Jyrki T. J. Penttinen
The fixed telecommunications networks have a long history. Since the beginning of the networks – which at the first phase were only dedicated point-to-point lines – they were utilized for telegrams via Morse codes. The voice was adapted to the wired environment after the invention of telephone devices. There have been various persons contributing to the initial innovation and enhancements of telephone equipment and systems in 1800 century. The first steps towards the communication lines were taken in 1870s. Since then, the wired lines and networks have been utilized for voice calls along with the deployment of the commercial systems. The voice is still an essential service, although the end-user's connection point has been moved from the fixed lines towards wireless access in a very fast transition period during the 1990s, and remarkably towards IP solutions as of 2000s.
The elements of the fixed telephone network can be connected via various principles. The most important ones are bus, ring and star topologies. There are many other variants, too. The extreme representatives of these are the straight line connecting directly two devices, and at the other extreme, the open Internet with all the possible systems connected via IP.
The quality of service (QoS) has been one of the most important aspects of voice telephony networks. For that reason, it has been typical to assure functioning ...