Abstract: A method for analyzing Internet telephone quality and interference has developed that two-way voice and video quality between IP phones and a measurement instrument measures in real time along the actual communication path using loopback functions of the IP phones. When interference is detected, the interference source location is identified by checking whether the interference has occurred in the internal section of the IP phones or in the IP network section on the basis of loopback results of the IP phones and ping and trace route analysis in a section-based manner.