Chap 25


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Chap 25

  1. 1. Chapter 25 MultimediaTCP/IP Protocol Suite 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. OBJECTIVES: To show how audio/video files can be downloaded for future use or broadcast to clients over the Internet. The Internet can also be used for live audio/video interaction. Audio and video need to be digitized before being sent over the Internet. To discuss how audio and video files are compressed for transmission through the Internet. To discuss the phenomenon called Jitter that can be created on a packet-switched network when transmitting real-time data. To introduce the Real-Time Transport Protocol (RTP) and Real- Time Transport Control Protocol (RTCP) used in multimedia applications. To discuss voice over IP as a real-time interactive audio/video application.TCP/IP Protocol Suite 2
  3. 3. OBJECTIVES (continued): To introduce the Session Initiation Protocol (SIP) as an application layer protocol that establishes, manages, and terminates multimedia sessions. To introduce quality of service (QoS) and how it can be improved using scheduling techniques and traffic shaping techniques. To discuss Integrated Services and Differential Services and how they can be implemented. To introduce Resource Reservation Protocol (RSVP) as a signaling protocol that helps IP create a flow and makes a resource reservation.TCP/IP Protocol Suite 3
  4. 4. 25.1 Introduction Chapter Outline 25.2 Dig itizing Audio and V ideo 25.3 Audio/V ideo Compres s ion 25.4 S treaming S tored Audio/V ideo 25.5 S treaming Liv e Audio/V ideo 25.6 Real-Time Interactiv e Audio/V ideo 25.7 RTPTCP/IP Protocol Suite 25.8 RTCP 4
  5. 5. Chapter 25.9 V oice Over IP Outline 25.10 Quality of S erv ice ( continued) 25.11 Integ rated S erv ices 25.12 Differentiated S erv icesTCP/IP Protocol Suite 5
  6. 6. 25-1 INTRODUCTION We can divide audio and video services into three broad categories: streaming stored audio/video, streaming live audio/video, and interactive audio/video, as shown in Figure 25.1. Streaming means a user can listen (or watch) the file after the downloading has started.TCP/IP Protocol Suite 6
  7. 7. Figure 25.1 Internet audio/videoTCP/IP Protocol Suite 7
  8. 8. Note Streaming stored audio/video refers to on-demand requests for compressed audio/video files.TCP/IP Protocol Suite 8
  9. 9. Note Streaming live audio/video refers to the broadcasting of radio and TV programs through the Internet.TCP/IP Protocol Suite 9
  10. 10. Note Interactive audio/video refers to the use of the Internet for interactive audio/video applications.TCP/IP Protocol Suite 10
  11. 11. 25-2 DIGITIZING AUDIO AND VIDEO Before audio or video signals can be sent on the Internet, they need to be digitized. We discuss audio and video separately.TCP/IP Protocol Suite 11
  12. 12. Topics Discussed in the Section  Digitizing Audio  Digitizing VideoTCP/IP Protocol Suite 12
  13. 13. Note Compression is needed to send video over the Internet.TCP/IP Protocol Suite 13
  14. 14. 25-3 AUDIO AND VIDEO COMPRESSION To send audio or video over the Internet requires compression. In this section, we first discuss audio compression and then video compression.TCP/IP Protocol Suite 14
  15. 15. Topics Discussed in the Section  Audio Compression  Video CompressionTCP/IP Protocol Suite 15
  16. 16. Figure 25.2 JPEG gray scaleTCP/IP Protocol Suite 16
  17. 17. Figure 25.3 JPEG processTCP/IP Protocol Suite 17
  18. 18. Figure 25.4 Case 1: uniform gray scaleTCP/IP Protocol Suite 18
  19. 19. Figure 25.5 Case2: two sectionsTCP/IP Protocol Suite 19
  20. 20. Figure 25.6 Case 3 : gradient gray scaleTCP/IP Protocol Suite 20
  21. 21. Figure 25.7 Reading the tableTCP/IP Protocol Suite 21
  22. 22. Figure 25.8 MPEG framesTCP/IP Protocol Suite 22
  23. 23. Figure 25.9 MPEG frame constructionTCP/IP Protocol Suite 23
  24. 24. 25-4 STREAMING STORED AUDIO/VIDEO Now that we have discussed digitizing and compressing audio/video, we turn our attention to specific applications. The first is streaming stored audio and video. Downloading these types of files from a Web server can be different from downloading other types of files. To understand the concept, let us discuss three approaches, each with a different complexity.TCP/IP Protocol Suite 24
  25. 25. Topics Discussed in the Section  First Approach: Using a Web Server  Second Approach: Using a Web Server with Metafile  Third Approach: Using a Media Server  Fourth Approach: Using a Media Server and RTSPTCP/IP Protocol Suite 25
  26. 26. Figure 25.10 Using a Web server GET: audio/video file 1 RESPONSE 2 3 Audio/video o fileTCP/IP Protocol Suite 26
  27. 27. Figure 25.11 Using a Web server with a metafile GET: metafile 1 RESPONSE 2 3 Metafile GET: audio/video file 4 RESPONSE 5TCP/IP Protocol Suite 27
  28. 28. Figure 25.12 Using a media server GET: metafile 1 RESPONSE 2 3 Metafile GET: audio/video file 4 RESPONSE 5TCP/IP Protocol Suite 28
  29. 29. Figure 25.13 Using a media server and RSTP GET: metafile 1 RESPONSE 2 3 Metafile SETUP 4 RESPONSE 5 PLAY 6 RESPONSE 7 Audio/video Stream TEARDOWN 8 RESPONSE 9TCP/IP Protocol Suite 29
  30. 30. 25-5 STREAMING LIVE AUDIO/VIDEO Streaming live audio/video is similar to the broadcasting of audio and video by radio and TV stations. Instead of broadcasting to the air, the stations broadcast through the Internet. There are several similarities between streaming stored audio/video and streaming live audio/video. They are both sensitive to delay; neither can accept retransmission. However, there is a difference. In the first application, the communication is unicast and on-demand. In the second, the communication is multicastTCP/IP Protocol Suite 30
  31. 31. 25-6 REAL-TIME INTERACTIVE AUDIO/VIDEO In real-time interactive audio/video, people communicate with one another in real time. The Internet phone or voice over IP is an example of this type of application. Video conferencing is another example that allows people to communicate visually and orally.TCP/IP Protocol Suite 31
  32. 32. Topics Discussed in the Section  CharacteristicsTCP/IP Protocol Suite 32
  33. 33. Figure 25.14 Time relationshipTCP/IP Protocol Suite 33
  34. 34. Note Jitter is introduced in real-time data by the delay between packets.TCP/IP Protocol Suite 34
  35. 35. Figure 25.15 JitterTCP/IP Protocol Suite 35
  36. 36. Figure 25.16 TimestampTCP/IP Protocol Suite 36
  37. 37. Note To prevent jitter, we can timestamp the packets and separate the arrival time from the playback time.TCP/IP Protocol Suite 37
  38. 38. Figure 25.17 Playback bufferTCP/IP Protocol Suite 38
  39. 39. Note A playback buffer is required for real-time traffic.TCP/IP Protocol Suite 39
  40. 40. Note A sequence number on each packet is required for real-time traffic.TCP/IP Protocol Suite 40
  41. 41. Note Real-time traffic needs the support of multicasting.TCP/IP Protocol Suite 41
  42. 42. Note Translation means changing the encoding of a payload to a lower quality to match the bandwidth of the receiving network.TCP/IP Protocol Suite 42
  43. 43. Note Mixing means combining several streams of traffic into one stream.TCP/IP Protocol Suite 43
  44. 44. Note TCP, with all its sophistication, is not suitable for interactive multimedia traffic because we cannot allow retransmission of packets.TCP/IP Protocol Suite 44
  45. 45. Note UDP is more suitable than TCP for interactive traffic. However, we need the services of RTP, another transport layer protocol, to make up for the deficiencies of UDP.TCP/IP Protocol Suite 45
  46. 46. 25-7 RTP Real-time Transport Protocol (RTP) is the protocol designed to handle real-time traffic on the Internet. RTP does not have a delivery mechanism (multicasting, port numbers, and so on); it must be used with UDP. RTP stands between UDP and the application program. The main contributions of RTP are timestamping, sequencing, and mixing facilities.TCP/IP Protocol Suite 46
  47. 47. Topics Discussed in the Section  RTP Packet Format  UDP PortTCP/IP Protocol Suite 47
  48. 48. Figure 25.18 RTP packet header formatTCP/IP Protocol Suite 48
  49. 49. Figure 25.19 RTP packet header formatTCP/IP Protocol Suite 49
  50. 50. TCP/IP Protocol Suite 50
  51. 51. Note RTP uses a temporary even-numbered UDP port.TCP/IP Protocol Suite 51
  52. 52. 25-8 RTCP RTP allows only one type of message, one that carries data from the source to the destination. In many cases, there is a need for other messages in a session. These messages control the flow and quality of data and allow the recipient to send feedback to the source or sources. Real- Time Transport Control Protocol (RTCP) is a protocol designed for this purpose.TCP/IP Protocol Suite 52
  53. 53. Topics Discussed in the Section  Sender Report  Receiver Report  Source Description Message  Bye Message  Application-Specific Message  UDP PortTCP/IP Protocol Suite 53
  54. 54. Figure 25.20 RTCP message typesTCP/IP Protocol Suite 54
  55. 55. Note RTCP uses an odd-numbered UDP port number that follows the port number selected for RTP.TCP/IP Protocol Suite 55
  56. 56. 25-9 VOICE OVER IP Let us concentrate on one real-time interactive audio/video application: voice over IP, or Internet telephony. The idea is to use the Internet as a telephone network with some additional capabilities. Instead of communicating over a circuit-switched network, this application allows communication between two parties over the packet-switched Internet. Two protocols have been designed to handle this type of communication: SIP and H.323. We briefly discuss both.TCP/IP Protocol Suite 56
  57. 57. Topics Discussed in the Section  SIP  H.323TCP/IP Protocol Suite 57
  58. 58. Figure 25.21 SIP messagesTCP/IP Protocol Suite 58
  59. 59. Figure 25.22 SIP formatsTCP/IP Protocol Suite 59
  60. 60. Figure 25.23 SIP simple session INVITE: address, options Establishing OK: address ACK Communicating Exchanging audio Terminating BYETCP/IP Protocol Suite 60
  61. 61. Figure 25.24 Tracking the callee INVITE Lookup Reply INVITE OK OK ACK ACK Exchanging audio BYETCP/IP Protocol Suite 61
  62. 62. Figure 25.25 H.323 architectureTCP/IP Protocol Suite 62
  63. 63. Figure 25.26 H.323 protocolsTCP/IP Protocol Suite 63
  64. 64. Figure 25.27 H.323 example Find IP address of gatekeeper Q.931 message for setup RTP for audio exchange RTCP for management Q.931 message for terminationTCP/IP Protocol Suite 64
  65. 65. 25-10 QUALITY OF SERVICE Quality of service (QoS) is an internetworking issue that has been discussed more than defined. We can informally define quality of service as something a flow of data seeks to attain. Although QoS can be applied to both textual data and multimedia, it is more an issue when we are dealing with multimedia.TCP/IP Protocol Suite 65
  66. 66. Topics Discussed in the Section  Flow Characteristics  Flow Classes  Techniques to Improve QoS  Resource Reservation  Admission ControlTCP/IP Protocol Suite 66
  67. 67. Figure 25.28 Flow characteristicsTCP/IP Protocol Suite 67
  68. 68. Figure 25.29 FIFO queuesTCP/IP Protocol Suite 68
  69. 69. Figure 25.30 Priority queuesTCP/IP Protocol Suite 69
  70. 70. Figure 25.31 Weighted fair queuingTCP/IP Protocol Suite 70
  71. 71. Figure 25.32 Leaky bucketTCP/IP Protocol Suite 71
  72. 72. Figure 25.33 Leaky bucket implementationTCP/IP Protocol Suite 72
  73. 73. Note A leaky bucket algorithm shapes bursty traffic into fixed-rate traffic by averaging the data rate. It may drop the packets if the bucket is full.TCP/IP Protocol Suite 73
  74. 74. Figure 25.34 Token bucketTCP/IP Protocol Suite 74
  75. 75. Note The token bucket allows bursty traffic at a regulated maximum rate.TCP/IP Protocol Suite 75
  76. 76. 25-11 INTEGRATED SERVICES IP was originally designed for best-effort delivery. This means that every user receives the same level of services. This type of delivery does not guarantee the minimum of a service, such as bandwidth, to applications such as real-time audio and video. Integrated Services, sometimes called IntServ, is a flow-based QoS model, which means that a user needs to create a flow, a kind of virtual circuit, from the source to the destination and inform all routers of the resource requirement.TCP/IP Protocol Suite 76
  77. 77. Topics Discussed in the Section  Signaling  Flow Specification  Admission  Service Classes  RSVP  Problems with Integrated ServicesTCP/IP Protocol Suite 77
  78. 78. Note Integrated Services is a flow-based QoS model designed for IP.TCP/IP Protocol Suite 78
  79. 79. Figure 25.35 Path messagesTCP/IP Protocol Suite 79
  80. 80. Figure 25.36 Resv messagesTCP/IP Protocol Suite 80
  81. 81. Figure 25.37 Reservation mergingTCP/IP Protocol Suite 81
  82. 82. Figure 25.38 Reservation stylesTCP/IP Protocol Suite 82
  83. 83. 25-12 DIFFERENTIATED SERVICES Differentiated Services (DS or Diffserv) was introduced by the IETF (Internet Engineering Task Force) to handle the shortcomings of Integrated Services.TCP/IP Protocol Suite 83
  84. 84. Topics Discussed in the Section  DS FieldTCP/IP Protocol Suite 84
  85. 85. Note Differentiated Services is a class-based QoS model designed for IP.TCP/IP Protocol Suite 85
  86. 86. Figure 25.39 DS fieldTCP/IP Protocol Suite 86
  87. 87. Figure 25.40 Traffic conditionerTCP/IP Protocol Suite 87