VoIP Voice and Fax Signal Processing

5.8 PLC SUMMARY AND DISCUSSION

Packet loss is the major contributor of voice quality degradation as given in this chapter and in Chapter 20. Packet losses are unavoidable at least in certain conditions. The first priority should be to avoid end-to-end packet drops, and that may be achieved at the cost of actions that may increase end-to-end delay. In most situations, increasing delay is more acceptable than packet drop and PLC action. Packet drop contributions are usually apportioned to the IP network, but in practice, major contributions happen with Internet service provider interfaces, terminating routers, and end VoIP systems. IP backbone networks provide much better performance in transporting IP packets. In practice, the user will have a tendency to increase data applications that quickly consume the available bandwidth. Activating QoS mechanisms and ensuring effective functioning of these in real deployments, reserving enough bandwidth for voice, monitoring, and dynamically incorporating feedback, can improve on packet delivery. When more bandwidth is available for VoIP, using lower compression codecs such as G.711 and G.722 (in wideband) is more beneficial to counter packet losses. Applying transmitter–receiver-based FEC, redundancies are preferred, but in the case of bandwidth constraints, these techniques degrade packet delivery. Hence, it is essential to operate with codec and packetization combinations that allow some reasonable margin within the available bandwidth. ...