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Transmisión de Datos Multimedia – – Master IC 2007/2008 Tema 0: Transmisión de Datos Multimedia  Clases de aplicaciones.

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Presentation on theme: "Transmisión de Datos Multimedia – – Master IC 2007/2008 Tema 0: Transmisión de Datos Multimedia  Clases de aplicaciones."— Presentation transcript:

1 Transmisión de Datos Multimedia – – Master IC 2007/2008 Tema 0: Transmisión de Datos Multimedia  Clases de aplicaciones multimedia  Redes basadas en IP y QoS Computer Networking: A Top Down Approach Featuring the Internet, 3 rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.

2 Transmisión de Datos Multimedia - Master IC 2007/ What is multimedia?  Definition of multimedia Hard to find a clear-cut definition In general, multimedia is an integration of text, graphics, still and moving images, animation, sounds, and any other medium where every type of information can be represented, stored, transmitted and processed digitally  Characteristics of multimedia Digital – key concept Integration of multiple media type, usually including video or/and audio May be interactive or non-interactive

3 Transmisión de Datos Multimedia - Master IC 2007/ Various Media Types  Text, Graphics, image, video, animation, sound, etc.  Classifications of various media types Captured vs. synthesized media Captured media (natural) : information captured from the real world –Example: still image, video, audio Synthesized media (artificial) : information synthesize by the computer –Example: text, graphics, animation Discrete vs. continuous media Discrete media: space-based, media involve the space dimension only –Text, Image, Graphics Continuous media: time-based, media involves both the space and the time dimension –Video, Sound, Animation

4 Transmisión de Datos Multimedia - Master IC 2007/ Classification of Media Type Sound Video Image Animation Text Graphics Captured From real world Synthesized By computer Discrete Continuous

5 Transmisión de Datos Multimedia - Master IC 2007/ Text  Plain text Unformatted Characters coded in binary form ASCII code All characters have the same style and font  Rich text Formatted Contains format information besides codes for characters No predominant standards Characters of various size, shape and style, e.g. bold, colorful

6 Transmisión de Datos Multimedia - Master IC 2007/ Plain Text vs. Rich Text An example of Plain text Example of Rich text

7 Transmisión de Datos Multimedia - Master IC 2007/ Graphics  Revisable document that retains structural information  Consists of objects such as lines, curves, circles, etc  Usually generated by graphic editor of computer programs Example of graphics (FIG file)

8 Transmisión de Datos Multimedia - Master IC 2007/ Images  2D matrix consisting of pixels Pixel—smallest element of resolution of the image One pixel is represented by a number of bits Pixel depth– the number of bits available to code the pixel  Have no structural information  Two categories: scanned vs. synthesized still image Computer software Computer software Capture and A/D conversion Capture and A/D conversion Digital still image Synthesized image Scanned image Camera

9 Transmisión de Datos Multimedia - Master IC 2007/ Images (cont.)  Examples of images Binary image – pixel depth 1 Gray-scale – pixel depth 8 Color image – pixel depth 24 Binary image Gray-scale imagecolor image

10 Transmisión de Datos Multimedia - Master IC 2007/ Video vs. Animation  Both images and graphics can be displayed as a succession of view which create an impression of movement  Video – moving images or moving pictures Captured or Synthesized Consists of a series of bitmap images Each image is called a frame Frame rate: the speed to playback the video (frame per second)  Animation – moving graphics Generated by computer program (animation authoring tools) Consists of a set of objects The movements of the objects are calculated and the view is updated at playback

11 Transmisión de Datos Multimedia - Master IC 2007/ Sound  1-D time-based signal  Speech vs. non-speech sound Speech – supports spoken language and has a semantic content Non-speech – does not convey semantics in general  Natural vs. structured sound Natural sound – Recorded/generated sound wave represented as digital signal Example: Audio in CD, WAV files Structured sound – Synthesize sound in a symbolic way Example: MIDI file

12 Transmisión de Datos Multimedia - Master IC 2007/ Networked Multimedia  Local vs. networked multimedia Local: storage and presentation of multimedia information in standalone computers Sample applications: DVD Networked: involve transmission and distribution of multimedia information on the network Sample applications: videoconferencing, web video broadcasting, multimedia , etc. Internet Video server Image server A scenario of multimedia networking

13 Transmisión de Datos Multimedia - Master IC 2007/ Consideration of Networked Multimedia  Requirements of multimedia applications on the network Typically delay sensitive end-to-end delay delay jitter: –Jitter is the variability of packet delays within the same packet stream Quality requirement Satisfactory quality of media presentation Synchronization requirement Continuous requirement (no jerky video/audio) Can tolerant some degree of information loss

14 Transmisión de Datos Multimedia - Master IC 2007/ Technologies of Multimedia Networking  Challenges of multimedia networking 1.Conflict between media size and bandwidth limit of the network 2.Conflict between the user requirement of multimedia application and the best-effort network 3.How to meet different requirements of different users?  Media compression – reduce the data volume Address the 1st challenge Image compression Video compression Audio compression  Multimedia transmission technology Address the 2nd and 3rd challenges Protocols for real-time transmission Rate / congestion control Error control

15 Transmisión de Datos Multimedia - Master IC 2007/ Multimedia Networking Systems  Live media transmission system Capture, compress, and transmit the media on the fly (example?)  Send stored media across the network Media is pre-compressed and stored at the server. This system delivers the stored media to one or multiple receivers. (example?)  Differences between the two systems For live media delivery: Real-time media capture, need hardware support Real-time compression– speed is important Compression procedure can be adjusted based on network conditions For stored media delivery Offline compression – better compression result is important Compression can not be adjusted during transmission

16 Transmisión de Datos Multimedia - Master IC 2007/ Classes of multimedia applications  Streaming stored audio and video  Streaming live audio and video  Real-time interactive audio and video

17 Transmisión de Datos Multimedia - Master IC 2007/ Streaming Stored Multimedia: What is it? 1. video recorded 2. video sent 3. video received, played out at client Cumulative data streaming: at this time, client playing out early part of video, while server still sending later part of video network delay time t>0 100%

18 Transmisión de Datos Multimedia - Master IC 2007/ Streaming vs. Download of Stored Multimedia Content  Download: Receive entire content before playback begins High “start-up” delay as media file can be large ~ 4GB for a 2 hour MPEG II movie  Streaming: Play the media file while it is being received Reasonable “start-up” delays Reception Rate >= playback rate. Why?

19 Transmisión de Datos Multimedia - Master IC 2007/ Streaming Stored Multimedia: Interactivity VCR-like functionality: client can pause, rewind, FF, push slider bar 10 sec initial delay OK 1-2 sec until command effect OK RTSP often used (more later) timing constraint for still-to-be transmitted data: in time for playout

20 Transmisión de Datos Multimedia - Master IC 2007/ constant bit rate video transmission Cumulative data time variable network delay client video reception constant bit rate video playout at client client playout delay buffered video Streaming Multimedia: Client Buffering  Client-side buffering, playout delay compensate for network- added delay, delay jitter

21 Transmisión de Datos Multimedia - Master IC 2007/ Streaming Multimedia: Client Buffering  Client-side buffering, playout delay compensate for network-added delay, delay jitter buffered video variable fill rate, x(t) constant drain rate, d

22 Transmisión de Datos Multimedia - Master IC 2007/ Interactive, Real-Time Multimedia applications: IP telephony, video conference, distributed interactive worlds  end-end delay requirements: audio: < 150 msec good, < 400 msec OK includes application-level (packetization) and network delays higher delays noticeable, impair interactivity  session initialization how does callee advertise its IP address, port number, encoding algorithms?

23 Transmisión de Datos Multimedia - Master IC 2007/ Internet multimedia: simplest approach audio, video not streamed:  no, “pipelining,” long delays until playout!  audio or video stored in file  files transferred as HTTP object received in entirety at client then passed to player

24 Transmisión de Datos Multimedia - Master IC 2007/ Progressive Download  browser GETs metafile  browser launches player, passing metafile  player contacts server  server downloads audio/video to player

25 Transmisión de Datos Multimedia - Master IC 2007/ Streaming from a streaming server  This architecture allows for non-HTTP protocol between server and media player  Can also use UDP instead of TCP.

26 Transmisión de Datos Multimedia - Master IC 2007/ Multimedia Over Today’s Internet  TCP/UDP/IP: “best-effort service”  no guarantees on delay, loss  But multimedia apps requires QoS and level of performance to be effective!  Today’s Internet multimedia applications use application-level techniques to mitigate (as best possible) effects of delay, loss

27 Transmisión de Datos Multimedia - Master IC 2007/ Streaming Multimedia: UDP or TCP? UDP  server sends at rate appropriate for client (oblivious to network congestion!) often send rate = encoding rate = constant rate then, fill rate = constant rate - packet loss  short playout delay (2-5 seconds) to compensate for network delay jitter  error recover: time permitting TCP  send at maximum possible rate under TCP  fill rate fluctuates due to TCP congestion control  larger playout delay: smooth TCP delivery rate  HTTP/TCP passes more easily through firewalls

28 Transmisión de Datos Multimedia - Master IC 2007/ Multimedia, Quality of Service: What is it? Multimedia applications: network audio and video (“continuous media”) network provides application with level of performance needed for application to function. QoS

29 Transmisión de Datos Multimedia - Master IC 2007/ Improving QOS in IP Networks  Thus far: “making the best of best effort”  Future: next generation Internet with QoS guarantees RSVP: signaling for resource reservations Differentiated Services: differential guarantees Integrated Services: firm guarantees  simple model for sharing and congestion studies:

30 Transmisión de Datos Multimedia - Master IC 2007/ Principles for QOS Guarantees  Example: 1Mbps IPphone, FTP share 1.5 Mbps link. bursts of FTP can congest router, cause audio loss want to give priority to audio over FTP packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly Principle 1

31 Transmisión de Datos Multimedia - Master IC 2007/ Principles for QOS Guarantees (more)  what if applications misbehave (audio sends higher than declared rate) policing: force source adherence to bandwidth allocations  marking and policing at network edge: similar to ATM UNI (User Network Interface) provide protection (isolation) for one class from others Principle 2

32 Transmisión de Datos Multimedia - Master IC 2007/ Principles for QOS Guarantees (more)  Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation While providing isolation, it is desirable to use resources as efficiently as possible Principle 3

33 Transmisión de Datos Multimedia - Master IC 2007/ Principles for QOS Guarantees (more)  Basic fact of life: can not support traffic demands beyond link capacity Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs Principle 4

34 Transmisión de Datos Multimedia - Master IC 2007/ Summary of QoS Principles


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