Tutorial 11 Solutions

Question 1 Q1. What is meant by interactivity for streaming stored audio/video? What is meant by interactivity for real-time interactive audio/video? –Streaming stored audio/video: pause/resume, re-positioning, fast-forward –real-time interactive audio and video: people communicating and responding in real time.

Question 2 Q2. Three camps were discussed for improving the internet so that it better supports multimedia applications. Briefly summarize the views of each camp. –Camp 1 (caching, multicast): No fundamental changes in TCP/IP protocols; add bandwidth where needed; also use caching, content distribution networks, and multicast overlay networks. –Camp 2 (Reservation): Provide a network service that allows applications to reserve bandwidth in the network. –Camp 3 (Differentiated service): introduce simple classifying and policing schemes at the edge of the network, and give different datagrams different levels of service according to their class in the router queues.

Q3 Figures 1, 2, and 3 present three schemes for steaming stored media. What are the advantages and disadvantages of each scheme?

Fig.1 Audio or video stored in files Files transferred as HTTP objects –Received in entirety at client –Then passed to player simple, doesn’t require meta file or streaming server Audio and video are not streamed, long delays before playout Figure 1: A naive implementation for audio streaming

Fig.2 Procedures: –Browser gets metafile –Browser passes the metafile to the player –Player contacts with web server –Web server streams the media files allows media player to interact directly with the web server, doesn’t require a streaming server The media stream can only transmitted by HTTP protocol (over TCP link), heavy burden for the web server Figure 2: Web server sends audio/video directly to the media player

Fig.3 Different from Fig.2, the player directly contacts streaming server Allow application- specific non-HTTP protocol between client and server (UDP link), load balance Figure 3: Streaming from a streaming server to a media player

Case Study YouTube, Google Video, Yahoo! Video and etc. –Video files are stored in streaming server in the format of Flash Video (*.flv) –Users play videos using Adobe Flash Player embedded in browser –Video streams through HTTP protocol Microsoft Media Service (MMS) –Media files are stored in Windows Media Server –Media streams through MMS protocol transported via UDP/TCP port 1755 See more: /wiki/Flash_Video /wiki/Flash_Video See more: /wiki/Microsoft_Media _Services

Q4 Q4. Consider the client buffer shown in Figure 4. Suppose that the streaming system uses the option that the server pushes the media into the socket as quickly as possible. Suppose the available TCP bandwidth >> d most of the time. Also suppose that the client buffer can hold only about one-third of the media. Describe how x(t) and the contents of the client buffer will evolve over time. Figure 4: Client buffer being filled at rate x(t) and drained at rate d

Q.4 x(t) will continue to grow until the client buffer becomes full. Once the client buffer becomes full, the client application will drain the receive TCP buffer at rate d. TCP flow control will then throttle the sender's transmission rate so that the average of x(t) after the client buffer becomes full is approximately d.