 frames, but each and every frame has a standard header. A typical data frame is illustrated in Figure 15.2. The frame structure and how various octets of the header (and tail) are utilized are governed by a protocol. Various data protocols were discussed in Chapters 11-13. We can clearly see that there are two differing philosophies here, one for data commu- nication and the other for digital voice. Digital voice is sometimes called "circuit-switched voice." A majority in the telecommunication community saw how advantageous it would be if we could marry the two and make them one. That is one singular approach for both voice and data. Meanwhile, data hobbyists were trying to transmit voice using data packets. The Internet protocol (IP) became the data protocol of choice, but there were many drawbacks. 15.3 DRAWBACKS AND CHALLENGES FOR TRANSMITTING VOICE ON DATA PACKETS We have come to measure "quality" of packetized voice service by the equivalent service offered by the switched digital network (i.e., the PSTN), sometimes called G.711 (1) 15.4 VOIP, INTRODUCTORY TECHNICAL DESCRIPTION service. The user expects a quality of service (QoS) as good as he or she would get on a PSTN dial-up connection. To achieve this goal, voice-over IP (VoIP) designers were faced with the following degradations: Mouth-to-ear delay Impact of errored frames (packets) Lost frames (packets) Variation of packet arrival time, jitter buffering Prioritizing VoIP traffic over regular Internet and data services Talker echo Distortion Sufficient bit rate capacity on interconnecting transmission media Voice coding algorithm standardization Optimized standard packet payload size Packet overhead Silence suppression 15.4 VOIP, INTRODUCTORY TECHNICAL DESCRIPTION Figure 15.3 shows a simplified block diagram of VoIP operation from an analog signal deriving from a standard telephone, which is digitized and transmitted over the Internet via a conversion device. Then, at the distant end, it is converted back to analog telephony using a similar device suit