PCM codec standardized by ITU-T as G.711 in 1988. Because of the very low bit error rate performance of PSTN circuits, no error concealment scheme is provided by G.711 when it is used for PSTN. Examples of other voice codecs standardized over the years by ITU-T for PSTN include G.726 and G.727, both of which were standardized in 1990 and use ADPCM technique. G.726 covers the transmission of voice at rates of 16, 24, 32, and 40 kbit/s, but the most commonly used mode is 32 kbit/s on international trunks in phone networks. Digital cellular networks technologies have experienced enormous growth over the last decade. Digital cellular networks provide wireless voice connectivity by employing high- quality voice codecs as well as error detection and concealment techniques. The future per- formance can be improved by unequal protection of the bits according to their importance. In addition, because errors mainly appear as bursts in wireless channels, interleaving be used to spread the errors, which can effectively simplify the concealment process. The adaptive multirate wideband (AMR-WB) speech coder, standardized by the 3GPP, is one of the major codecs used for digital cellular networks. This coder operates at rates of Chapter 1 Voice Transmission 6.6, 8.85, 12.65, 14.25, 15.85, 18.25, 19.85, 23.05, and 23.85 kbit/s and is based on an algebraic CELP (ACELP) analysis-by-synthesis codec. The coder is also standardized by ITU-T as G.722-2. Mention should also be made of cdma2000 Variable-Rate Multimode Wideband (VRM-WB) speech-coding standard, which was standardized by the 3GPP2. The codec has five different modes and can be used to provide different Quality-of-Service (QoS) levels. Voice over Internet Protocol (VoIP) is a revolutionary technology that enables the use of packet-switched networks to deliver voice traffic. Examples of considerations in design- ing good VoIP systems include voice quality, latency, jitter, packet loss performance, and packetization. Today's VoIP product offerings typically include G.711, G.72