Transcript tut11_sol_modified

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 applicationspecific 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
See more:
server in the format of Flash Video
http://en.wikipedia.org
(*.flv)
– Users play videos using Adobe Flash /wiki/Flash_Video
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:
http://en.wikipedia.org
/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.