l see in Section 3.6. Data trans- mission is bursty by nature. Sometimes we may copy a file across the net- work, whereas at other times we may work locally with our workstation. When many different applications are integrated into multimedia com- munications, both basic types of service requirements of constant-bit-rate voice and bursty data have to be fulfilled and we need a concept that is able to meet both types of requirements. In Table 3.1 different applications are compared from the communica- tion requirements point of view. The applications are ordinary speech, computer-aided design (CAD) (a service in which high-resolution graphical information is transmitted), moving images (video), file transfer, and multi- media with integrated video, voice, and data. The importance of the trans- mission requirements for each application is explained next. Data Rate or Bandwidth Requirement Voice communication usually requires a constant data rate of 64 Kbps or less and high-resolution video a constant data rate of 2 Mbps or higher over the network. Characteristics of data communication are very different, for exam- ple, file transfer requires high-bit-rate transmission only during download, and high-resolution graphics on a Web page require high-data-rate transmis- sion only when we download a new page. When we are reading a Web page we do not need transmission capacity at all. To define data transmission Signals Carried over the Network Table 3.1 Communication Requirements of Different Applications Transmission Interactive Characteristics Voice Video Transfer Media Bandwith Low, fixed Very high, High, High, variable requirement fixed variable Data loss Tolerant Tolerant Nontolerant Tolerant or tolerance nontolerant Fixed delay Low delay Tolerant Tolerant Low delay tolerance Variable delay Tolerant tolerance Peak information Fixed Fixed Very high capacity, we sometimes use the term bandwidth instead of data rate because these terms are closely related to each other, as we will see in Chapter 4. Data Loss Tolerance N