Speech Coding Challenges in VoIP Applications

Voice over IP is gaining increased momentum with the wide deployment of data networks and the desirability to bundle voice and data services over the same media. Central to the success of this concept is the underlying quality of speech, which is function of the coding schemes used, and the effectiveness of mitigating the effects of such impairments as packet loss, delay, jitter, echo, noise and tandeming on the perceived quality of speech to the end user. The first part of the paper outlines the peculiarities of VoIP systems, the attributes of speech coders and the factors affecting speech quality. The second part discusses current methods being used and some of the remaining hurdles yet to overcome in the quest for proper IP-based telephony.