VoIP Voice Quality White Paper

Good or excellent voice quality is a key competitive differentiator for VoIP service providers, and poor voice quality can become a crippling disadvantage for VoIP services that compete with each other, or with the Public Switched Telephone Network (PSTN).

The most competitive VoIP offerings are those that recognize and address the fundamental difference between voice quality and IP quality. Quality of Service (QoS) provisions for packet-based networks serve to minimize packet loss, delay, and jitter. But even in a QoS-enhanced under-subscribed packet network, VoIP voice quality can be unacceptably poor. Voice impairments that cause voice quality problems include hybrid and acoustic echo (exacerbated by delay), low signal-to-noise ratios, a lack of “comfort” noise, signal levels that are not normalized for consistent volume, use of low bitrate codecs or flawed transcoding between codec types, and poor intelligibility resulting from inevitable packet loss.

Also, under-subscribing to enhance voice quality undermines the primary advantage of VoIP: the cost-effectiveness that is derived from statistical multiplexing gains found only in packet-based networks. So while packet-level QoS is certainly necessary, it is far from being sufficient.

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