Chapter 7: Multimedia, Quality Of Service: Chapter 7 .

Chapter 7: GoalsChapter 7: Multimedia, Quality of Service:What is it?Multimedia applications:network audio and video(“continuous media”)Principles Classify multimedia applications Identify the network services the apps need Making the best of best effort service Mechanisms for providing QoSProtocols and ArchitecturesQoS Specific protocols for best-effort Architectures for QoSnetwork providesapplication with level ofperformance needed forapplication to function.7: Multimedia Networking6-26:Wirel7-1MM Networking ApplicationsClasses of MM applications:1) Streaming stored audioand video2) Streaming live audio andvideo3) Real-time interactiveaudio and videoJitter is the variabilityof packet delays withinthe same packet streamStreaming Stored MultimediaFundamentalcharacteristics: Typically delay sensitive end-to-end delaydelay jitterinfrequent losses causeminor glitches Antithesis of data,which are loss intolerantbut delay tolerant.7: Multimedia Networking2. video2sent timing constraint for still-to-betransmitted data: in time for playout7: Multimedia Networking7-3Streaming Stored Multimedia:What is it?1. videorecordedStreaming: media stored at source transmitted to client streaming: client playout beginsbefore all data has arrived ButB t lossltolerant:t lt:Streaming Stored Multimedia: Interactivity networkdelay7-43. video received,played out at clienttimestreaming: at this time, clientplaying out early part of video,while server still sending laterpart of video7: Multimedia Networking7-5VCR-like functionality: client canpause, 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-betransmitted data: in time for playout7: Multimedia Networking7-61

Interactive, Real-Time MultimediaStreaming Live MultimediaExamples: Internet radio talk show Live sporting eventStreaming playback buffer playback can lag tens of seconds aftertransmission still have timing constraintInteractivity fast forward impossible rewind, pause possible! applications: IP telephony,video conference, distributedinteractive worlds end-end delay requirements: audio: 150 msec good, 400 msec OK includes application-level (packetization) and networkdelays higher delays noticeable, impair interactivity session initialization 7: Multimedia Networking7-7Integrated services philosophy: Fundamental changes inInternet so that apps canreserve end-to-endbandwidth Requires new, complexsoftwareftiin hhostst & routerstLaissez-faire no major changes more bandwidth whenneeded content distribution,application-layer multicastTCP/UDP/IP: “best-effort service”no guarantees on delay, loss?But you said multimedia apps requires ?Q S andQoSd llevell off performanceftto bbe? effective!?Today’s Internet multimedia applicationsuse application-level techniques to mitigate(as best possible) effects of delay, loss7: Multimedia Networking at constant rate telephone: 8,000samples/secCD music: 44,100psamples/sec Each sample quantized,i.e., rounded e.g., 28 256 possiblequantized values Each quantized valuerepresented by bits 8 bits for 256 values7: Multimedia Networking 7-10 Video is sequence ofsamples/sec, 256quantized values -- 64,000 bps Receiver converts itback to analog signal:images displayed atconstant rate e.g. 24 images/sec Digital image is array ofpixelssome quality reduction Each pixel representedExample rates CD: 1.411 Mbps MP3: 96, 128, 160 kbps Internet telephony:5.3 - 13 kbps7: Multimedia NetworkingWhat’s your opinion?A few words about video compression Example: 8,000 application layerDifferentiated servicesphilosophy: Fewer changes to Internetinfrastructure, yet provide1st and 2nd class service.7-9A few words about audio compression Analog signal sampled7-8How should the Internet evolve to bettersupport multimedia?Multimedia Over Today’s Internet how does callee advertise its IP address, portnumber, encoding algorithms?7: Multimedia Networkingby bits Redundancy spatial temporal7-11Examples: MPEG 1 (CD-ROM) 1.5Mbps MPEG2 (DVD) 3-6 Mbps MPEG4 (often used inInternet, 1 Mbps)Research: Layered (scalable) video adapt layers to availablebandwidth7: Multimedia Networking 7-122

Chapter 7 outlineStreaming Stored Multimedia 7.1 MultimediaNetworking Applications 7.2 Streaming storedaudio and video 7.3 Real-time Multimedia:Internet Phone study 7.4 Protocols for RealTime InteractiveApplications RTP,RTCP,SIP 7.6 Beyond BestEffort 7.7 Scheduling andPolicing Mechanisms 7.8 IntegratedServices andDifferentiatedServices 7.9 RSVPApplication-level streamingtechniques for making thebest out of best effortservice: client side buffering use of UDP versus TCP multiple encodings ofmultimediaMedia Player jitter removal decompression error concealment graphical user interfacew/ controls forinteractivity 7.5 DistributingMultimedia: contentdistribution networks7: Multimedia Networking 7-13Internet multimedia: simplest approach7: Multimedia Networking 7-14Internet multimedia: streaming approach audio or video stored in file files transferred as HTTP object received in entirety at clientthen passed to player browser GETs metafile browser launches player, passing metafileaudio, video not streamed: no, “pipelining,” long delays until playout! player contacts server server streams audio/video to player7: Multimedia Networking 7-15Streaming Multimedia: Client Bufferingconstant bitrate videotransmissionvariablenetworkd ldelay This architecture allows for non-HTTP protocol betweenserver and media playerclient videoreceptionconstant bitrate videoplayout at clientbuffeeredvideoStreaming from a streaming server7: Multimedia Networking 7-16timeclient playoutdelay Client-side buffering, playout delay compensate Can also use UDP instead of TCP.for network-added delay, delay jitter7: Multimedia Networking 7-177: Multimedia Networking 7-183

Streaming Multimedia: Client BufferingStreaming Multimedia: UDP or TCP?UDP server sends at rate appropriate for client (oblivious toconstantdrainrate, dvariable fillrate, x(t)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 networkd l jittdelayjitter error recover: time permittingTCPbufferedvideo send at maximum possible rate under TCP fill rate fluctuates due to TCP congestion control Client-side buffering, playout delay compensatefor network-added delay, delay jitter larger playout delay: smooth TCP delivery rate HTTP/TCP passes more easily through firewalls7: Multimedia Networking 7-19Streaming Multimedia: client rate(s)1.5 Mbps encoding28.8 Kbps encodingQ: how to handle different client receive ratecapabilities? 28.8 Kbps dialup 100Mbps EthernetA: server stores, transmits multiple copiesof video, encoded at different rates7: Multimedia Networking 7-20User Control of Streaming Media: RTSPHTTP Does not target multimediacontent No commands for fastforward, etc.RTSP: RFC 2326 Client-server applicationlayer protocol. For user to control display:rewind, fast forward,pause, resume,repositioning, etc What it doesn’t do: does not define howaudio/video is encapsulatedfor streaming over network does not restrict howstreamed media isttransported;t d it can bbetransported over UDP orTCP does not specify how themedia player buffersaudio/video7: Multimedia Networking 7-21RTSP: out of band controlFTP uses an “out-of-band”control channel: A file is transferred overone TCP connection. Control information(directory changes, filef renaming,m g,deletion,, fileetc.) is sent over aseparate TCP connection. The “out-of-band” and “inband” channels usedifferent port numbers.RTSP ExampleRTSP messages are also sentout-of-band: RTSP control messagesuse different port numbersthan the media stream:out-of-band. 7: Multimedia Networking 7-22Port 554 The media stream isScenario: metafile communicated to web browser browser launches player player sets up an RTSP control connection, dataconnectionconnct on to strstreamingam ng sserverr rconsidered “in-band”.7: Multimedia Networking 7-237: Multimedia Networking 7-244

Metafile ExampleRTSP Operation title Twister /title session group language en lipsync switch track type audioe "PCMU/8000/1"src "rtsp://audio.example.com/twister/audio.en/lofi" " t // dil/t i t / di/l fi" track type audioe "DVI4/16000/2" pt "90 DVI4/8000/1"src "rtsp://audio.example.com/twister/audio.en/hifi" /switch track type "video/jpeg"src "rtsp://video.example.com/twister/video" /group /session 7: Multimedia Networking 7-25RTSP Exchange Example7: Multimedia Networking 7-26Chapter 7 outlineC: SETUP rtsp://audio.example.com/twister/audio RTSP/1.0Transport: rtp/udp; compression; port 3056; mode PLAYS: RTSP/1.0 200 1 OKSession 4231C: PLAY rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0Session: 4231RRange:npt 00C: PAUSE rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0Session: 4231Range: npt 37 7.1 Multimedia NetworkingApplications 7.2 Streaming storedaudio and video 7.3 Real-time Multimedia:Internet Phone case study 7.4 Protocols for RealTime InteractiveApplications C: TEARDOWN rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0Session: 4231S: 200 3 OKRTP,RTCP,SIPEffort 7.7 Scheduling andPolicing Mechanisms 7.8 IntegratedServices andDifferentiatedServices 7.9 RSVP 7.5 DistributingMultimedia: contentdistribution networks7: Multimedia Networking 7-27Real-time interactive applications 7.6 Beyond Best7: Multimedia Networking 7-28Interactive Multimedia: Internet PhoneIntroduce Internet Phone by way of an example PC-2-PC phone instant messagingservices are providingthis PC-2-phoneGoing to now look ata PC-2-PC Internetphone example indetail speaker’s audio: alternating talk spurts, silentperiods. Dialpad Net2phone videoconference withWebcams 64 kbps during talk spurt pkts generated only during talk spurts20 msec chunks at 8 Kbytes/sec: 160 bytes data application-layer header added to each chunk. Chunk header encapsulated into UDP segment. application sends UDP segment into socket every20 msec during talkspurt.7: Multimedia Networking 7-297: Multimedia Networking 7-305