Voice over Internet Protocol (VoIP) is a technology that transports voice data packets across packetswitched networks using the Internet Protocol (IP). Losing packets in the network is inevitable, and losing voice packets degrades audio quality. There are many loss-recovery techniques that designers can use to mitigate the undesired effects of packet loss. Some of these loss-recovery techniques use senderbased procedures, and others use receiver-based procedures.

We examine several well-known sender-based loss-recovery techniques that are feasible for realtime interactive VoIP applications. We analyze the bandwidth requirements, buffering delays, and perceptual sound qualities of these techniques. We report the effects that various types of loss conditions have on the effectiveness of these approaches in improving the Quality of Service (QoS) of VoIP.