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CS5229 Lecture 9: Simulating the Internet

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CS5229 Lecture 9: Simulating the Internet

  1. 1. Methodologies for Networking Research 17 October 2008 CS5229, Semester 1, 2008/09 1
  2. 2. Measurementquot; V. Paxson. quot;End-to-end Internet packet dynamics,”quot; J. Padhye, V. Firoiu, D. Towesley, and J. Kurose quot;Modeling TCP Throughput: A Simple Model and its Empirical Validation,” 17 October 2008 CS5229, Semester 1, 2008/09 2
  3. 3. “Reality Check” Are our assumptions reasonable? Is our mathematical model a good estimation of the real world? 17 October 2008 CS5229, Semester 1, 2008/09 3
  4. 4. e.g., from Paxson’s studyquot; 1. packet losses are busrtyquot; 2. OTT != RTT/2 17 October 2008 CS5229, Semester 1, 2008/09 4
  5. 5. 17 October 2008 CS5229, Semester 1, 2008/09 5
  6. 6. 17 October 2008 CS5229, Semester 1, 2008/09 6
  7. 7. Experimentationquot; 
 e.g., V. Jacobson. “Congestion Control and Avoidancequot; 17 October 2008 CS5229, Semester 1, 2008/09 7
  8. 8. Deal with implementation issues Sometimes unforeseen complexities (e.g. own research experience in Unreliable TCP) 17 October 2008 CS5229, Semester 1, 2008/09 8
  9. 9. Understand the Behavior of Systems Some systems are too complex to understand with “thought experiments” alone. 17 October 2008 CS5229, Semester 1, 2008/09 9
  10. 10. 17 October 2008 CS5229, Semester 1, 2008/09 10
  11. 11. 17 October 2008 CS5229, Semester 1, 2008/09 11
  12. 12. Analysisquot; D. Chiu and R. Jain, quot;Analysis of the increase and decrease algorithms for congestion avoidance in computer networks,”quot; J. Padhye, V. Firoiu, D. Towesley, and J. Kurose quot;Modeling 
 TCP Throughput: A Simple Model and its Empirical Validation,” 17 October 2008 CS5229, Semester 1, 2008/09 12
  13. 13. Explore with Complete Control We can understand the basic forces that affect the system. e.g. TCP throughput is inversely propotional to √p 17 October 2008 CS5229, Semester 1, 2008/09 13
  14. 14. Simplify complex systemsquot; If too simplified, important behavior could be missed (TCP throughput without timeout) 17 October 2008 CS5229, Semester 1, 2008/09 14
  15. 15. Simulationquot; K. Fall and S. Floyd, quot;Simulation-based comparison of Tahoe, Reno, and SACK TCP,quot;quot; S. Floyd, K. Fall, quot;Promoting the Use of End-to-End Congestion Control in the Internet,”quot; S. Floyd, V. Jacobson, quot;Random Early Detection Gateways for Congestion Avoidance,quot; 17 October 2008 CS5229, Semester 1, 2008/09 15
  16. 16. Check Correctness of Analysisquot; If simulation uses the same assumptions/model as the analysis, this simply verifies the correctness of the mathematical derivations. 17 October 2008 CS5229, Semester 1, 2008/09 16
  17. 17. Check Correctness of Analysisquot; Simulation can relax some assumptions, use more complex models, etc. to test the limits of analysis. (Real measurement/experiments still needed to check the usefulness of analysis results) 17 October 2008 CS5229, Semester 1, 2008/09 17
  18. 18. Explore Complex Systemsquot; Some systems are too difficult/impossible to analyzed e.g. Internet 17 October 2008 CS5229, Semester 1, 2008/09 18
  19. 19. Helps Develop Intuitionquot; 17 October 2008 CS5229, Semester 1, 2008/09 19
  20. 20. Measurementquot; Experimentationquot; } Real World Analysisquot; Simulationquot; } Abstract Model 17 October 2008 CS5229, Semester 1, 2008/09 20
  21. 21. “Difficulties in Simulating the Internet” quot; Sally Floyd, Van Paxsonquot; ACM/IEEE TON, 9(4) August 2001
  22. 22. Why is Internet hard to simulate? 17 October 2008 CS5229, Semester 1, 2008/09 22
  23. 23. 1.! Internet is diverse 17 October 2008 CS5229, Semester 1, 2008/09 23
  24. 24. End-hosts: phones, desktops, servers, iPod, Wii 17 October 2008 CS5229, Semester 1, 2008/09 24
  25. 25. Links: Ethernet, WiFi, Satellite, Dial-up, 3G 17 October 2008 CS5229, Semester 1, 2008/09 25
  26. 26. Transport: TCP variants, UDP, DCCP 17 October 2008 CS5229, Semester 1, 2008/09 26
  27. 27. Applications: games, videos, web, ftp, bittorrent 17 October 2008 CS5229, Semester 1, 2008/09 27
  28. 28. 2.! Internet is huge 17 October 2008 CS5229, Semester 1, 2008/09 28
  29. 29. 570,937,778
 Number of Hosts as of July 2008 http://www.isc.org/index.pl?/ops/ds/host-count-history.php 17 October 2008 CS5229, Semester 1, 2008/09 29
  30. 30. 3.! Internet is changing 17 October 2008 CS5229, Semester 1, 2008/09 30
  31. 31. http://www.isc.org/ds/ 17 October 2008 CS5229, Semester 1, 2008/09 31
  32. 32. 17 October 2008 CS5229, Semester 1, 2008/09 32 http://www.dtc.umn.edu/mints/
  33. 33. Median File Transfer Time Size March 1998 10.9 kB December 1998 5.6 kB December 1999 10.9 kB June 2000 62 kB November 2000 10 kB Measurement at LBNL: Statistical property of Internet changes as well.
  34. 34. Why is Internet hard to simulate?quot; 1. Heterogeneous quot; 2. Huge quot; 3. Changing 17 October 2008 CS5229, Semester 1, 2008/09 34
  35. 35. Suppose you come up with the greatest BitTorrent improvement ever.. 17 October 2008 CS5229, Semester 1, 2008/09 35
  36. 36. You want to simulate it to make sure it works before you release it (and call the press) 17 October 2008 CS5229, Semester 1, 2008/09 36
  37. 37. What Internet topology should you use in your simulation? How end hosts are connected? What are the properties of the links? 17 October 2008 CS5229, Semester 1, 2008/09 37
  38. 38. Topology changes constantlyquot; Companies keep info secretsquot; Routes may changequot; Routes may be asymmetric 17 October 2008 CS5229, Semester 1, 2008/09 38
  39. 39. You will need to simulate over a wide range of connectivity and link properties 17 October 2008 CS5229, Semester 1, 2008/09 39
  40. 40. Suppose you come up with the greatest TCP optimization ever.. 17 October 2008 CS5229, Semester 1, 2008/09 40
  41. 41. You want to know if it is fair to existing TCP versions before you write your SIGCOMM paper.. 17 October 2008 CS5229, Semester 1, 2008/09 41
  42. 42. Which TCP version to use? 17 October 2008 CS5229, Semester 1, 2008/09 42
  43. 43. Using “fingerprinting”, 831 different TCP implementations and versions are identified. 17 October 2008 CS5229, Semester 1, 2008/09 43
  44. 44. Which to use? Which to ignore? 17 October 2008 CS5229, Semester 1, 2008/09 44
  45. 45. What applications to run? What type of traffic to generate?quot; Telnet? FTP? Web? BitTorrent? Skype? 17 October 2008 CS5229, Semester 1, 2008/09 45
  46. 46. How congested should the network be? 17 October 2008 CS5229, Semester 1, 2008/09 46
  47. 47. How congested should the network be? 17 October 2008 CS5229, Semester 1, 2008/09 47
  48. 48. Example from Sally Floyd: RED vs DropTail 17 October 2008 CS5229, Semester 1, 2008/09 48
  49. 49. 17 October 2008 CS5229, Semester 1, 2008/09 49
  50. 50. 17 October 2008 CS5229, Semester 1, 2008/09 50
  51. 51. Example from Sally Floyd: Using TFRC for VoIP 17 October 2008 CS5229, Semester 1, 2008/09 51
  52. 52. 17 October 2008 CS5229, Semester 1, 2008/09 52
  53. 53. 17 October 2008 CS5229, Semester 1, 2008/09 53
  54. 54. We can focus our simulation on dominant technology/application today.. 17 October 2008 CS5229, Semester 1, 2008/09 54
  55. 55. TCP: NewReno SACKSquot; OS: Windows Linuxquot; Applications: Web, FTP 17 October 2008 CS5229, Semester 1, 2008/09 55
  56. 56. What about tomorrow? 17 October 2008 CS5229, Semester 1, 2008/09 56
  57. 57. WiMax? quot; Sensors? quot; Virtual World?quot; DCCP? 17 October 2008 CS5229, Semester 1, 2008/09 57
  58. 58. 10 years ago, you came up with a router mechanism to improve TCP Reno.. quot; No one cares today. 17 October 2008 CS5229, Semester 1, 2008/09 58
  59. 59. How to verify the simulator itself? 17 October 2008 CS5229, Semester 1, 2008/09 59
  60. 60. So, how? 17 October 2008 CS5229, Semester 1, 2008/09 60
  61. 61. Looking for Invariants 17 October 2008 CS5229, Semester 1, 2008/09 61
  62. 62. 1. Diurnal Patterns 17 October 2008 CS5229, Semester 1, 2008/09 62
  63. 63. 17 October 2008 CS5229, Semester 1, 2008/09 63
  64. 64. hour #constrained ---- ------------ 00 139 2.5% -----------------------------------------------------X 01 144 2.6% ------------------------------------------------------X 02 146 2.6% -------------------------------------------------------X 03 140 2.5% -----------------------------------------------------X 04 119 2.1% ---------------------------------------------X 05 89 1.6% ----------------------------------X 06 69 1.2% --------------------------X 07 55 1.0% ---------------------X 08 45 0.8% -----------------X 09 40 0.7% ---------------X 10 40 0.7% ---------------X 11 42 0.8% ----------------X 12 51 0.9% -------------------X 13 57 1.0% ---------------------X 14 68 1.2% --------------------------X 15 75 1.3% ----------------------------X 16 77 1.4% -----------------------------X 17 92 1.6% -----------------------------------X 18 98 1.8% -------------------------------------X 19 105 1.9% ----------------------------------------X 20 108 1.9% -----------------------------------------X 21 113 2.0% -------------------------------------------X 22 124 2.2% -----------------------------------------------X 23 134 2.4% ---------------------------------------------------X U Waterloo Data 24 Oct 2007 17 October 2008 CS5229, Semester 1, 2008/09 64
  65. 65. 2. Self-Similar Traffic 17 October 2008 CS5229, Semester 1, 2008/09 65
  66. 66. The traffic is bursty regardless of time scale 17 October 2008 CS5229, Semester 1, 2008/09 66
  67. 67. Wikipedia 17 October 2008 CS5229, Semester 1, 2008/09 67
  68. 68. 3. Poisson Session Arrival 17 October 2008 CS5229, Semester 1, 2008/09 68
  69. 69. Remote logins, starting FTP, beginning of web surfing etc. 17 October 2008 CS5229, Semester 1, 2008/09 69
  70. 70. (so are dead light bulbs, spelling mistakes, etc.) 17 October 2008 CS5229, Semester 1, 2008/09 70
  71. 71. 4. Log-normal Duration 17 October 2008 CS5229, Semester 1, 2008/09 71
  72. 72. 5. Heavy Tail Distributions 17 October 2008 CS5229, Semester 1, 2008/09 72
  73. 73. Self-Similarity in World Wide Web Traffic: Evidence and Possible Causes, by Mark E. Crovella and Azer Bestavros 17 October 2008 CS5229, Semester 1, 2008/09 73
  74. 74. 1. Looking for Invariants 17 October 2008 CS5229, Semester 1, 2008/09 74
  75. 75. 2. Explore Parameter Space 17 October 2008 CS5229, Semester 1, 2008/09 75
  76. 76. Change one parameter,quot; fix the rest 17 October 2008 CS5229, Semester 1, 2008/09 76
  77. 77. Explore a wide range of values 17 October 2008 CS5229, Semester 1, 2008/09 77
  78. 78. 3. Use Traces 17 October 2008 CS5229, Semester 1, 2008/09 78
  79. 79. e.g. collects traces of web sessions, video files, VoIP traffic 17 October 2008 CS5229, Semester 1, 2008/09 79
  80. 80. Use it to simulate the traffic source 17 October 2008 CS5229, Semester 1, 2008/09 80
  81. 81. But must be careful about traffic shaping and user/application adaptation. 17 October 2008 CS5229, Semester 1, 2008/09 81
  82. 82. e.g. traces collected during non- congested time should not be use to simulate congested networks. 17 October 2008 CS5229, Semester 1, 2008/09 82
  83. 83. 4. publish simulator script for others to verify 17 October 2008 CS5229, Semester 1, 2008/09 83
  84. 84. Conclusion 17 October 2008 CS5229, Semester 1, 2008/09 84
  85. 85. Simulation is useful but needs to do it properly 17 October 2008 CS5229, Semester 1, 2008/09 85
  86. 86. Be careful about your simulation model: you want it to be as simple as possible, but not simpler. 17 October 2008 CS5229, Semester 1, 2008/09 86
  87. 87. Be careful about your conclusion: “A is 13.5% better than B” is probably useless. 17 October 2008 CS5229, Semester 1, 2008/09 87
  88. 88. “A is 13.5% better than B under these environment”quot; is better but not general 17 October 2008 CS5229, Semester 1, 2008/09 88
  89. 89. Not really for quantitative results, but more for 17 October 2008 CS5229, Semester 1, 2008/09 89
  90. 90. understanding the dynamics,quot; illustrate a point,quot; explore unexpected behavior. 17 October 2008 CS5229, Semester 1, 2008/09 90

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