 of the jitter buffer size A G.711 codec produces audio uncompressed to Loss of packets (due to excessive delay, etc.) 64 kbps Aggressiveness of silence suppression AG.729 codec produces audio compressed to 8 kbps Performance bottleneck in the PC AG.723 codec produces audio compressed to 5.3 to 6.3 kbps Lower-speed PCs (or PCs with slow hard drives) may have adverse interactions with sound playback and re- Table 3.3-1 provides comparisons of several voice quality cording. This can cause breaks in received or transmitted considerations associated with some of the codecs. These audio. The best thing to do in this situation is to increase qualities are based on an industry guideline known as the the processor speed, increase the amount of RAM, and/ Mean Opinion Score (MOS). The MOS is a subjective or reduce the number of applications competing for the scale for rating voice quality from 1 to 5, where 4 or better processor or hard drive resources. One notable resource is considered "toll quality" or the equivalent of the quality consumer is the Microsoft Find Fast program that in the U.S. public switched telephone network (PSTN). launches from the Startup folder (and runs in the back- Generally, G.711 is used within LANs because ground). This application periodically re-indexes the bandwidth is abundant and inexpensive, whereas G.729 hard drive and consumes significant PC resources in the is used across WAN links because of the bandwidth process. savings and reliable voice quality. Bandwidth requirements PC Considerations using IP softphone The bandwidth available to the user is very important. Access to the network using slower connections, such as IP softphones are software on a PC that simulates a dial-up connections, will degrade voice quality. The best voice quality is achieved in both LANs and WANs when telephone. The "perceived" audio/voice quality at the the bandwidth is "owned" by the customer. Customer- owned bandwidth can be shaped to optimize VoIP traffic. Conversely, bandwidth that is not controlled, lik