While lounging in bed or riding buses and subways, people in all corners of the world are currently using the Internet to watch movies and television shows on demand. Internet movie and television distribution companies such as Netflix and Amazon in North America and Youku and Kankan in China have practically become household names. But people are not only watching Internet videos, they are using sites like YouTube to upload and distribute their own user-generated content, becoming Internet video producers as well as consumers. Moreover, network applications such as Skype, Google Talk, and WeChat (enormously popular in China) allow people to not only make “telephone calls” over the Internet, but to also enhance those calls with video and multi-person conferencing. In fact, we predict that by the end of the current decade most of the video consumption and voice conversations will take place end-to-end over the Internet, more typically to wireless devices connected to the Internet via cellular and WiFi access networks. Traditional telephony and broadcast television are quickly becoming obsolete.
We begin this chapter with a taxonomy of multimedia applications in Section 9.1. We’ll see that a multimedia application can be classified as either streaming stored audio/video, conversational voice/video-over-IP, or streaming live audio/video. We’ll see that each of these classes of applications has its own unique service requirements that differ significantly from those of traditional elastic applications such as e-mail, Web browsing, and remote login. In Section 9.2, we’ll examine video streaming in some detail. We’ll explore many of the underlying principles behind video streaming, including client buffering, prefetching, and adapting video quality to available bandwidth. In Section 9.3, we investigate conversational voice and video, which, unlike elastic applications, are highly sensitive to end-to-end delay but can tolerate occasional loss of data. Here we’ll examine how techniques such as adaptive playout, forward error correction, and error concealment can mitigate against network-induced packet loss and delay. We’ll also examine Skype as a case study. In Section 9.4, we’ll study RTP and SIP, two popular protocols for real-time conversational voice and video applications. In Section 9.5, we’ll investigate mechanisms within the network that can be used to distinguish one class of traffic (e.g., delay-sensitive applications such as conversational voice) from another (e.g., elastic applications such as browsing Web pages), and provide differentiated service among multiple classes of traffic.