The Application Layer

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The Application Layer

• Chapter 7-3

Institute of Information Science and Technology .
Chengdu University YiYong 2008?2?25?
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Teaching object

• Through this section of the study , student
  should be understand the basic concepts of the
  data link layer, on top of stop waiting for the
  agreement

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Focus and Difficulties

• Multimedia

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7.4 Multimedia

• Introduction to Audio
• Audio Compression
• Streaming Audio
• Internet Radio
• Voice over IP
• Introduction to Video
• Video Compression
• Video on Demand
• The MBone The Multicast Backbone

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7.4.1 Introduction to Audio

• (a) A sine wave. (b) Sampling the sine wave.
  (c) Quantizing the samples to 4 bits.

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7.4.2 Audio Compression

• (a) The threshold of audibility as a function of
  frequency.
• (b) The masking effect.

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7.4.3 Streaming Audio

• A straightforward way to implement clickable
  music on a Web page.

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Streaming Audio (2)
When packets carry alternate samples, the loss of
a packet reduces the temporal resolution rather
than creating a gap in time.
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Streaming Audio (3)

• The media player buffers input from the media
  server and plays from the buffer rather than
  directly from the network.

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Streaming Audio (4)

• RTSP commands from the player to the server.

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7.4.4 Internet Radio

• A student radio station.

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7.4.5 Voice over IP

• The H323 architectural model for Internet
  telephony.

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Voice over IP (2)

• The H323 protocol stack.

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Voice over IP (3)

• Logical channels between the caller and callee
  during a call.

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SIP The Session Initiation Protocol

• The SIP methods defined in the core specification.

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SIP (2)

• Use a proxy and redirection servers with SIP.

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Comparison of H.323 and SIP
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7.4.6 Video Analog Systems

• The scanning pattern used for NTSC video and
  television.

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The JPEG Standard

• The operation of JPEG in lossy sequential mode.

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The JPEG Standard (2)

• (a) RGB input data.
• (b) After block preparation.

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The JPEG Standard (3)
(b)
(a)

• (a) One block of the Y matrix.
• (b) The DTC coefficients.

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The JPEG Standard (4)

• Computation of the quantized DTC coefficients.

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The JPEG Standard (5)

• The order in which the quantized values are
  transmitted.

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The MPEG Standard

• Synchronization of the audio and video streams in
  MPEG-1.

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The MPEG Standard (2)

• Three consecutive frames.

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7.4.8 Video on Demand

• Overview of a video-on-demand system.

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Video Servers

• A video server storage hierarchy.

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Video Servers (2)

• The hardware architecture of a typical video
  server.

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7.4.9 The MBone The Multicast Backbone

• MBone consists of multicast islands connected by
  tunnels.