Noise and Voice Quality in VoIP Environments *
In many ways, noise reduction techniques in a Voice over Internet Protocol (VoIP) environment mirror those used in traditional voice transmission systems. This chapter describes VoIP technologies and deployments, introduces in more detail the signal distortion and conversational quality impairments that VoIP exhibits, and discusses some of the techniques being used to ameliorate these impairments. It provides an examination of measurement techniques that target the unique VoIP environment. In its most basic and generic form, a VoIP network consists of user endpoints connected to media gateways which, in turn, are connected to the IP signaling and media transport network. An increasing number of VoIP protocols provide the signaling, call services, audio/video stream transport and, in some cases, quality of service needed to successfully place and answer VoIP telephone calls. The two of the biggest challenges facing VoIP systems are listening/sound quality and conversational quality.