chap29.ppt

29.2
Figure 29.1 Internet audio/video

29.3
Streaming stored audio/video refers to
on-demand requests for compressed
audio/video files.
Note

29.4
Streaming live audio/video refers to the
broadcasting of radio and TV programs
through the Internet.
Note

29.5
Interactive audio/video refers to the use
of the Internet for interactive audio/video
applications.
Note

29.6
29-1 DIGITIZING AUDIO AND VIDEO
Before audio or video signals can be sent on the
Internet, they need to be digitized. We discuss audio
and video separately.
Digitizing Audio
Digitizing Video
Topics discussed in this section:

29.7
Compression is needed to send video
over the Internet.
Note

29.8
29-2 AUDIO AND VIDEO COMPRESSION
To send audio or video over the Internet requires
compression. In this section, we discuss audio
compression first and then video compression.
Audio Compression
Video Compression

29.9
Figure 29.2 JPEG gray scale

29.10
Figure 29.3 JPEG process

29.11
Figure 29.4 Case 1: uniform gray scale

29.12
Figure 29.5 Case 2: two sections

29.13
Figure 29.6 Case 3: gradient gray scale

29.14
Figure 29.7 Reading the table

29.16
Figure 29.9 MPEG frame construction

29.17
29-3 STREAMING STORED AUDIO/VIDEO
Now that we have discussed digitizing and
compressing audio/video, we turn our attention to
specific applications. The first is streaming stored
audio and video.
First Approach: Using a Web Server
Second Approach: Using a Web Server with a Metafile
Third Approach: Using a Media Server
Fourth Approach: Using a Media Server and RTSP

29.18
Figure 29.10 Using a Web server

29.19
Figure 29.11 Using a Web server with a metafile

29.20
Figure 29.12 Using a media server

29.21
Figure 29.13 Using a media server and RTSP

29.22
29-4 STREAMING LIVE AUDIO/VIDEO
Streaming live audio/video is similar to the
broadcasting of audio and video by radio and TV
stations. Instead of broadcasting to the air, the stations
broadcast through the Internet. There are several
similarities between streaming stored audio/video and
streaming live audio/video. They are both sensitive to
delay; neither can accept retransmission. However,
there is a difference. In the first application, the
communication is unicast and on-demand. In the
second, the communication is multicast and live.

29.23
29-5 REAL-TIME INTERACTIVE
AUDIO/VIDEO
In real-time interactive audio/video, people
communicate with one another in real time. The
Internet phone or voice over IP is an example of this
type of application. Video conferencing is another
example that allows people to communicate visually
and orally.
Characteristics

29.24
Figure 29.14 Time relationship

29.25
Jitter is introduced in real-time data by
the delay between packets.
Note

29.28
To prevent jitter, we can time-stamp the
packets and separate the arrival time
from the playback time.
Note

29.29
Figure 29.17 Playback buffer

29.30
A playback buffer is required for real-
time traffic.
Note

29.31
A sequence number on each packet is
required for real-time traffic.
Note

29.32
Real-time traffic needs the support of
multicasting.
Note

29.33
Translation means changing the
encoding of a payload to a lower
quality to match the bandwidth
of the receiving network.
Note

29.34
Mixing means combining several
streams of traffic into one stream.
Note

29.35
TCP, with all its sophistication, is not
suitable for interactive multimedia
traffic because we cannot allow
retransmission of packets.
Note

29.36
UDP is more suitable than TCP for
interactive traffic. However, we
need the services of RTP,
another transport layer
protocol, to make up
for the deficiencies
of UDP.
Note

29.37
29-6 RTP
Real-time Transport Protocol (RTP) is the protocol
designed to handle real-time traffic on the Internet.
RTP does not have a delivery mechanism; it must be
used with UDP. RTP stands between UDP and the
application program. The main contributions of RTP
are time-stamping, sequencing, and mixing facilities.
RTP Packet Format
UDP Port

29.39
Figure 29.19 RTP packet header format

29.40
Table 20.1 Payload types

29.41
RTP uses a temporary even-numbered
UDP port.
Note

29.42
29-7 RTCP
RTP allows only one type of message, one that carries
data from the source to the destination. In many cases,
there is a need for other messages in a session. These
messages control the flow and quality of data and
allow the recipient to send feedback to the source
or sources. Real-time Transport Control Protocol
(RTCP) is a protocol designed for this purpose.
Sender Report and Receiver Report
Messages
UDP Port

29.43
Figure 29.20 RTCP message types

29.44
RTCP uses an odd-numbered UDP port
number that follows the port number
selected for RTP.
Note

29.45
29-8 VOICE OVER IP
Let us concentrate on one real-time interactive
audio/video application: voice over IP, or Internet
telephony. The idea is to use the Internet as a
telephone network with some additional capabilities.
Two protocols have been designed to handle this type
of communication: SIP and H.323.
SIP
H.323

29.46
Figure 29.21 SIP messages

29.47
Figure 29.22 SIP formats

29.48
Figure 29.23 SIP simple session

29.49
Figure 29.24 Tracking the callee

29.50
Figure 29.25 H.323 architecture

29.51
Figure 29.26 H.323 protocols

29.52
Figure 29.27 H.323 example

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