rk when there is silence, resulting in additional bandwidth savings. The software Transcoding also measures the idle noise characteristics of the tele- phony interface. It reports this information to the Packet Transcoding is a voice signal converted from analog to Voice Protocol to relay this information to the remote digital or digital to analog (possibly with or without end for comfort noise generation when no voice is compression and decompression). If calls are routed present. using multiple voice coders, as in the case of call coverage Some VADs can cause voice clipping and can result in on an intermediary system back to a centralized voice poor voice quality, but the use of VAD can greatly con- mail system, the calls may experience multiple serve bandwidth and is therefore a very important detail CHAPTER 3.3 VolP Technology to consider when planning network bandwidth- PC endpoint is a function of at least four factors, as especially in the WAN. follows: 1. Transducer quality Duplex The selection of speaker and microphone or headset has an impact on the reproduction of the sound. The ideal LAN network for transporting VoIP traffic is 2. Sound card quality a network that is fully switched from end to end because There are several parameters that affect sound card it significantly reduces or eliminates collisions. A network quality. The most important is whether or not the that has shared segments (hub-based) can result in lower sound card supports full-duplex operation. voice quality due to excessive collisions and should be 3. End-to-end delay avoided. A PC can be a major component of delay in a con- versation. PC delay consists of the jitter buffer and sound system delays, as well as the number of other Codec selection processes running and the speed of the processor. Depending on the bandwidth availability and acceptable 4. Speech breakup voice quality, it might be worthwhile to select a codec Speech breakup may be the result of a number of that produces compressed audio. factors. Network jitter in excess