Packetization Interval (PI)

The PI represents directly how many speech frames there are in each packet. Similar to CLP, the overall effect of increasing PI tends to improve speech quality. This is clearly shown from Figures 7.1 and 7.2. However, for smaller value of LR, there is no noticeable improvement when changing PI. Its effect becomes more important for higher LR and smaller CLP. For higher value of CLP, there is no effect of PI on speech quality. We can see that, the effect of PI depends on the used codec and the value of LR. For example, using PCM at 5 % LR, only an improvement of 0.2 against 0.4 for LR=10 %. However, when using GSM, the improvements are 0.3 and 0.6. In addition, when the network conditions are bad, we can improve the quality by increasing the PI. For example, using ADPCM codec and when CLP=1, the quality is the same (3 points) when (LR=5 % and PI=20ms) and when (LR=10 % and PI=40ms). These observations are important, because unlike the network parameters (LR and CLP), which could not be modified except by using FEC or improving the network infrastructure, this parameter can be modified to improve the quality. Another advantage of increasing PI is to improve the network utilization as explained in Section 8.3.1. Our result we get here regarding this parameter is with agreement with that in [61].