This paper was presented at the 5th International Conference on Information Society and Technology (ICIST 2015) Kopaonik 8-11.March.2015, entitled "Measurement QoS Parameters of VoIP Codecs as a Function of the Network Traffic Level". And finally I want to thank Professor Zoran Velickovic from College of Applied Technical Sciences Nis, and my colleague engineer Ivan Perisic from Telekom Serbia who helped on this project.