Telephony is one of the biggest steps in human communication since the first words spoken.
Voice calls made human interaction possible as if the communication partner was in the same room, even if they are the furthest places of the world, and all this in real-time with no noticeable delay.
The development of new telecommunication solutions have been going unimaginably fast, trying to satisfy the ever-growing data-consumption demand that modern society creates.
Actually teal-time data transmission as a natural part of this growth is also facing with tough challenges.
As part of this evolution not only voice -- even more generally media -- transmission solutions have to be developed, but their monitoring, measurement solutions also had to built and refined.
They provide sufficient feedback to find weak points in our systems and to collect enough information about the possible areas of development, which ability is inevitable in this area.
In this thesis I try to summarise important historical milestones and actual state of telecommunication systems focusing on data transmission and call switching, and also to design and implement a measurement instrument, that will be capable of passive performance testing in VoIP systems.