Presentation on theme: "Tema 0: Transmisión de Datos Multimedia"— Presentation transcript:
1 Tema 0: Transmisión de Datos Multimedia Clases de aplicaciones multimediaRedes basadas en IP y QoSComputer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.
2 What is multimedia? Definition of multimedia Hard to find a clear-cut definitionIn 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 digitallyCharacteristics of multimediaDigital – key conceptIntegration of multiple media type, usually including video or/and audioMay be interactive or non-interactive
3 Various Media TypesText, Graphics, image, video, animation, sound, etc.Classifications of various media typesCaptured vs. synthesized mediaCaptured media (natural) : information captured from the real worldExample: still image, video, audioSynthesized media (artificial) : information synthesize by the computerExample: text, graphics, animationDiscrete vs. continuous mediaDiscrete media: space-based, media involve the space dimension onlyText, Image, GraphicsContinuous media: time-based, media involves both the space and the time dimensionVideo, Sound, Animation
4 Classification of Media Type SoundVideoImageAnimationTextGraphicsCapturedFrom real worldSynthesizedBy computerDiscreteContinuous
5 Text Plain text Rich text Unformatted Characters coded in binary form ASCII codeAll characters have the same style and fontRich textFormattedContains format information besides codes for charactersNo predominant standardsCharacters of various size, shape and style, e.g. bold, colorful
6 Plain Text vs. Rich TextAn example of Plain textExample of Rich text
7 Graphics Revisable document that retains structural information Consists of objects such as lines, curves, circles, etcUsually generated by graphic editor of computer programsExample of graphics (FIG file)
8 Images 2D matrix consisting of pixels Have no structural information Pixel—smallest element of resolution of the imageOne pixel is represented by a number of bitsPixel depth– the number of bits available to code the pixelHave no structural informationTwo categories: scanned vs. synthesized still imageComputersoftwareCapture andA/D conversionDigital still imageSynthesizedimageScannedCamera
10 Video vs. AnimationBoth images and graphics can be displayed as a succession of view which create an impression of movementVideo – moving images or moving picturesCaptured or SynthesizedConsists of a series of bitmap imagesEach image is called a frameFrame rate: the speed to playback the video (frame per second)Animation – moving graphicsGenerated by computer program (animation authoring tools)Consists of a set of objectsThe movements of the objects are calculated and the view is updated at playback
11 Sound 1-D time-based signal Speech vs. non-speech sound Speech – supports spoken language and has a semantic contentNon-speech – does not convey semantics in generalNatural vs. structured soundNatural sound – Recorded/generated sound wave represented as digital signalExample: Audio in CD, WAV filesStructured sound – Synthesize sound in a symbolic wayExample: MIDI file
12 Networked Multimedia Local vs. networked multimedia Image server Local: storage and presentation of multimedia information in standalone computersSample applications: DVDNetworked: involve transmission and distribution of multimedia information on the networkSample applications: videoconferencing, web video broadcasting, multimedia , etc.Image serverA scenario of multimedia networkingInternetVideo server
13 Consideration of Networked Multimedia Requirements of multimedia applications on the networkTypically delay sensitiveend-to-end delaydelay jitter:Jitter is the variability of packet delays within the same packet streamQuality requirementSatisfactory quality of media presentationSynchronization requirementContinuous requirement (no jerky video/audio)Can tolerant some degree of information loss
14 Technologies of Multimedia Networking Challenges of multimedia networkingConflict between media size and bandwidth limit of the networkConflict between the user requirement of multimedia application and the best-effort networkHow to meet different requirements of different users?Media compression – reduce the data volumeAddress the 1st challengeImage compressionVideo compressionAudio compressionMultimedia transmission technologyAddress the 2nd and 3rd challengesProtocols for real-time transmissionRate / congestion controlError control
15 Multimedia Networking Systems Live media transmission systemCapture, compress, and transmit the media on the fly (example?)Send stored media across the networkMedia is pre-compressed and stored at the server. This system delivers the stored media to one or multiple receivers. (example?)Differences between the two systemsFor live media delivery:Real-time media capture, need hardware supportReal-time compression– speed is importantCompression procedure can be adjusted based on network conditionsFor stored media deliveryOffline compression – better compression result is importantCompression can not be adjusted during transmission
16 Classes of multimedia applications Streaming stored audio and videoStreaming live audio and videoReal-time interactive audio and video
17 Streaming Stored Multimedia: What is it? 100%streaming: at this time, clientplaying out early part of video,while server still sending laterpart of video3. video received,played out at clientCumulative data2. videosent1. videorecordednetworkdelaytime
18 Streaming vs. Download of Stored Multimedia Content Download: Receive entire content before playback beginsHigh “start-up” delay as media file can be large~ 4GB for a 2 hour MPEG II movieStreaming: Play the media file while it is being receivedReasonable “start-up” delaysReception Rate >= playback rate. Why?
19 Streaming Stored Multimedia: Interactivity VCR-like functionality: client can pause, rewind, FF, push slider bar10 sec initial delay OK1-2 sec until command effect OKRTSP often used (more later)timing constraint for still-to-be transmitted data: in time for playout
22 Interactive, Real-Time Multimedia applications: IP telephony, video conference, distributed interactive worldsend-end delay requirements:audio: < 150 msec good, < 400 msec OKincludes application-level (packetization) and network delayshigher delays noticeable, impair interactivitysession initializationhow does callee advertise its IP address, port number, encoding algorithms?
23 Internet multimedia: simplest approach audio or video stored in filefiles transferred as HTTP objectreceived in entirety at clientthen passed to playeraudio, video not streamed:no, “pipelining,” long delays until playout!
24 Progressive Download browser GETs metafile browser launches player, passing metafileplayer contacts serverserver downloads audio/video to player
25 Streaming from a streaming server This architecture allows for non-HTTP protocol between server and media playerCan also use UDP instead of TCP.
26 Multimedia Over Today’s Internet TCP/UDP/IP: “best-effort service”no guarantees on delay, lossBut 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 Streaming Multimedia: UDP or TCP? server sends at rate appropriate for client (oblivious to network congestion!)often send rate = encoding rate = constant ratethen, fill rate = constant rate - packet lossshort playout delay (2-5 seconds) to compensate for network delay jittererror recover: time permittingTCPsend at maximum possible rate under TCPfill rate fluctuates due to TCP congestion controllarger playout delay: smooth TCP delivery rateHTTP/TCP passes more easily through firewalls
28 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 Improving QOS in IP Networks Thus far: “making the best of best effort”Future: next generation Internet with QoS guaranteesRSVP: signaling for resource reservationsDifferentiated Services: differential guaranteesIntegrated Services: firm guaranteessimple model for sharing and congestion studies:
30 Principles for QOS Guarantees Example: 1Mbps IPphone, FTP share 1.5 Mbps link.bursts of FTP can congest router, cause audio losswant to give priority to audio over FTPPrinciple 1packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly
31 Principles for QOS Guarantees (more) what if applications misbehave (audio sends higher than declared rate)policing: force source adherence to bandwidth allocationsmarking and policing at network edge:similar to ATM UNI (User Network Interface)Principle 2provide protection (isolation) for one class from others
32 Principles for QOS Guarantees (more) Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocationPrinciple 3While providing isolation, it is desirable to use resources as efficiently as possible
33 Principles for QOS Guarantees (more) Basic fact of life: can not support traffic demands beyond link capacityPrinciple 4Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs
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