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Tema 4: Protocolos de transporte con QoS

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Tema 4: Protocolos de transporte con QoS

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  1. Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2004. Tema 4:Protocolos de transporte con QoS Clases de aplicaciones multimedia Redes basadas en IP y QoS Gestión de los recursos: IntServ vs DiffServ RSVP RTP/RTCP: Transporte de flujos multimedia RTSP: Control de sesión y localización de medios Multicasting • Thanks to : • RADCOM technologies • H. Shulzrinne • Paul. E. Jones (from packetizer.com)

  2. 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. 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. Sound Video Animation Continuous Continuous Graphics Text Image Discrete Discrete Captured From real world Synthesized By computer Classification of Media Type

  5. 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. Plain Text vs. Rich Text An example of Plain text Example of Rich text

  7. 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. Digital still image Computer software Synthesized image Capture and A/D conversion Scanned image 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 Camera

  9. Gray-scale image color image Binary image Images (cont.) • Examples of images • Binary image – pixel depth 1 • Gray-scale – pixel depth 8 • Color image – pixel depth 24

  10. 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. 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. 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 Email, etc. Image server A scenario of multimedia networking Internet Video server

  13. 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. Technologies of Multimedia Networking • Challenges of multimedia networking • Conflict between media size and bandwidth limit of the network • Conflict between the user requirement of multimedia application and the best-effort network • 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. 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. Classes of multimedia applications • Streaming stored audio and video • Streaming live audio and video • Real-time interactive audio and video

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

  18. 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. 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. Client-side buffering, playout delay compensate for network-added delay, delay jitter client video reception constant bit rate video playout at client variable network delay buffered video client playout delay Streaming Multimedia: Client Buffering constant bit rate video transmission Cumulative data time

  21. Streaming Multimedia: Client Buffering • Client-side buffering, playout delay compensate for network-added delay, delay jitter constant drain rate, d variable fill rate, x(t) buffered video

  22. 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. audio or video stored in file files transferred as HTTP object received in entirety at client then passed to player Internet multimedia: simplest approach audio, video not streamed: • no, “pipelining,” long delays until playout!

  24. Progressive Download • browser GETs metafile • browser launches player, passing metafile • player contacts server • server downloads audio/video to player

  25. 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. 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. 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. Tema 4: Protocolos de transporte con QoS. Clases de aplicaciones multimedia Redes basadas en IP y QoS Gestión de los recursos: IntServ vs DiffServ RSVP RTP/RTCP: Transporte de flujos multimedia RTSP: Control de sesión y localización de medios Multicasting • Thanks to : • RADCOM technologies • H. Shulzrinne • Paul. E. Jones (from packetizer.com)

  29. Envío del primer bit del mensaje Primer bit del mensaje recibido Ultimo bit del mensaje recibido Mensaje listo para recepción Mensaje listo para envío Retardo de acceso Retardo de tránsito Retardo de transmisión Retardo de acceso Retardo extremo-a-extremo Requisitos de red. • Se definen 3 parámetros críticos que la red debería suministrar a las aplicaciones multimedia: • Productividad (Throughput) • Número de bits que la red es capaz de entregar por unidad de tiempo (tráfico soportado). • CBR (streams de audio y vídeo sin comprimir) • VBR (ídem comprimido) • Ráfagas (Peak Bit Rate y Mean Bit Rate) • Retardo de tránsito (Transit delay)

  30. Emisor 1 2 3 t Receptor 1 2 3 D1 D2 = D1 D3 > D1 t Requisitos de red (II). • Varianza del retardo (Jitter) • Define la variabilidad del retardo de una red. • Jitter físico (redes de conmutación de circuito) • Suele ser muy pequeño (ns) • LAN jitter (Ethernet, FDDI). • Jitterfísico + tiempo de acceso al medio. • Redes WAN de conmutación de paquete (IP, X.25, FR) • Jitter físico + tiempo de acceso + retardo de conmutación de paquete en conmutadores de la red.

  31. Internet y las aplicaciones multimedia • ¿Qué podemos añadir a IP para soportar los requerimientos de las aplicaciones multimedia? • Técnicas de ecualización de retardos (buffering) • Protocolos de transporte que se ajusten mejor a las necesidades de las aplicaciones multimedia: • RTP (Real-Time Transport Protocol) RFC 1889. • RTSP (Real-Time Streaming Protocol) RFC 2326. • Técnicas de control de admisión y reserva de recursos (QoS) • RSVP (Resource reSerVation Protocol) RFC 2205 • Arquitecturas y protocolos específicos: • Protocolos SIP (RFC 2543), SDP (RFC 2327), SAP (RFC 2974), etc.. • ITU H.323

  32. Internet Protocols Slide thanks to Henning Schulzrinne

  33. QoS network provides application with level of performance needed for application to function. Multimedia, Quality of Service: What is it? Multimedia applications: network audio and video (“continuous media”)

  34. 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:

  35. 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 Principle 1 packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly

  36. 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) Principle 2 provide protection (isolation) for one class from others

  37. Principles for QOS Guarantees (more) • Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation Principle 3 While providing isolation, it is desirable to use resources as efficiently as possible

  38. Principles for QOS Guarantees (more) • Basic fact of life: can not support traffic demands beyond link capacity Principle 4 Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs

  39. Summary of QoS Principles

  40. Tema 4: Protocolos de transporte con QoS. Clases de aplicaciones multimedia Redes basadas en IP y QoS Gestión de los recursos: IntServ vs DiffServ RSVP RTP/RTCP: Transporte de flujos multimedia RTSP: Control de sesión y localización de medios Multicasting • Thanks to : • RADCOM technologies • H. Shulzrinne • Paul. E. Jones (from packetizer.com)

  41. Scheduling And Policing Mechanisms • scheduling: choose next packet to send on link • FIFO (first in first out) scheduling: send in order of arrival to queue • discard policy: if packet arrives to full queue: who to discard? • Tail drop: drop arriving packet • priority: drop/remove on priority basis • random: drop/remove randomly

  42. Scheduling Policies: more Priority scheduling: transmit highest priority queued packet • multiple classes, with different priorities • class may depend on marking or other header info, e.g. IP source/dest, port numbers, etc..

  43. Scheduling Policies: still more round robin scheduling: • multiple classes • cyclically scan class queues, serving one from each class (if available)

  44. Scheduling Policies: still more Weighted Fair Queuing: • generalized Round Robin • each class gets weighted amount of service in each cycle

  45. Policing Mechanisms • Goal: limit traffic to not exceed declared parameters • Three common-used criteria: • (Long term) Average Rate: how many pkts can be sent per unit time (in the long run) • crucial question: what is the interval length: 100 packets per sec or 6000 packets per min have same average! • Peak Rate: e.g., 6000 pkts per min. (ppm) avg.; 1500 pps peak rate • (Max.) Burst Size: max. number of pkts sent consecutively (with no intervening idle)

  46. Policing Mechanisms Token Bucket: limit input to specified Burst Size and Average Rate. • bucket can hold b tokens • tokens generated at rate r token/sec unless bucket full • over interval of length t: number of packets admitted less than or equal to (r t + b).

  47. token rate, r arriving traffic bucket size, b per-flow rate, R WFQ D = b/R max Policing Mechanisms (more) • token bucket, WFQ combine to provide guaranteed upper bound on delay, i.e., QoS guarantee!

  48. IETF Integrated Services • architecture for providing QOS guarantees in IP networks for individual application sessions • resource reservation: routers maintain state info of allocated resources, QoS req’s • admit/deny new call setup requests: Question: can newly arriving flow be admitted with performance guarantees while not violated QoS guarantees made to already admitted flows?

  49. Resource reservation call setup, signaling (RSVP) traffic, QoS declaration per-element admission control • QoS-sensitive scheduling (e.g., WFQ) Intserv: QoS guarantee scenario request/ reply

  50. Call Admission Arriving session must : • declare its QOS requirement • R-spec: defines the QOS being requested • characterize traffic it will send into network • T-spec: defines traffic characteristics • signaling protocol: needed to carry R-spec and T-spec to routers (where reservation is required) • RSVP