yption used with VPNs can add signif- discussed the needs of the voice packets and how those icant latency to voice streams, adversely affecting the needs can affect the quality of the voice transmission. We voice quality. Also, VPNs generally run over the also discussed the various protocols and methodologies Internet. Because there is no control over QoS used to provide for good-quality voice in an IP network. parameters for traffic crossing the Internet, voice The last section of the chapter also provided some rec- quality may suffer due to excessive packet loss, delay, ommendations for the design and implementation of and jitter. a converged VoIP network. In this chapter, we have discussed the special issues in- The last section of the chapter also provided some volved in the transmission of voice, a real-time applica- recommendations for the design and implementation of tion, over an IP network, a non-real-time media. We a converged VoIP network. Chapter 3.4 Channel protection fundamentals Raouf Hamzaoui, Vladimir Stankovié, Zixiang Xiong, Kannan Ramchandran, Rohit Puri, Abhik Majumdar, and Jim Chou 3.4.1 Introduction speaks of soft decision decoding. The channel decoder tries to recover the input to the channel encoder from the In many ways, the Internet (or a wireless network for output of the demodulator. Finally, the source decoder that matter) can be regarded simply as a communication produces an estimate of the information sequence. channel in a classical communication system. This In this chapter, we look in detail at the basic constit- chapter discusses the fundamentals of channel pro- uents of a communication system. In Section 3.4.2, we tection that lie beneath the error control techniques used briefly explain the notions of entropy of an information to communicate multimedia over the Internet and source, mutual information, rate-distortion function, wireless networks. and capacity of a channel. These notions are needed to The goal of a classical communication system is to introduce four fundamenta