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Voice Feature Guide 01

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When a network or a device loses packets, the voice quality deteriorates. In practice, packet loss is inevitable. If the packet loss concealment (PLC) is enabled to compensate the signals, however, the impact of packet loss on the voice quality is reduced and the success rates of FoIP and MoIP services increases in the case of packet loss. Voice IP data is transmitted using Real-Time Transport Protocol (RTP). The DSP chip detects the sequence number of received RTP packets. If the DSP chip detects packet loss, it automatically constructs voice data based on a configured compensation algorithm and sends the data to the TDM side.

Three compensation modes are available:
  • Compensate the lost packet with the silence.
  • Compensate the lost packet with the previous packet.
  • Compensate the lost packet with a similar packet that is calculated based on the energies of the previous packet and the subsequent packet (as described in G.711 Appendix I).
The third mode consumes the most DSP resources, but improves the voice quality in the most satisfying manner. The first mode consumes the least DSP resources, but improves the voice quality in the least satisfying manner. Figure 1-132 shows the packet loss compensation using the previous packet.
Figure 1-132 Packet loss compensation using the previous packet
When the IP network quality is poor, if the number of consecutively lost RTP packets is greater than 2, the voice quality is still poor even if the PLC is enabled.

Reference Standards and Protocols

G.711 Appendix I

Updated: 2019-02-22

Document ID: EDOC1100067358

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