Analysis on Influence of ADPCM Voice Packets on the Quality of VoIP

This paper analyzes how the major factors of ADPCM (Adaptive Differential Pulse Code Modulation) voice packets affect the voice quality of VoIP (Voice over Internet Protocol) on packet switched network. Empirical studies are done with commercial VoIP systems in which voice data is coded with PCM and ADPCM, and packetized. The coded voice packets are transmitted over the Internet using the UDP protocol. The transmitted packets which are exposed with network delay and packet loss due to the unsafe transmission protocol are reconstructed at the receiver side. The quality of reconstructed voice is analyzed using the MNB (Measuring Normal Block) method instead of the popular MOS (Mean of Score). The MNB method is modified to compare original voice and reconstructed voice in an offline manner. Packet size and allowable network delay vary in the acceptable range to investigate how they affect the quality of VoIP system.