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Dude, Where is My Packet?

Dude, Where is My Packet?. Overview. Characteristics of the Internet General techniques Error recovery for audio Effect of loss on MPEG Error recovery for MPEG. Loss Characteristics of The Internet. Characteristics of Internet. 60-70% of paths do not show any loss

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Dude, Where is My Packet?

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  1. Dude, Where is My Packet?

  2. Overview • Characteristics of the Internet • General techniques • Error recovery for audio • Effect of loss on MPEG • Error recovery for MPEG NUS.SOC.CS5248 OOI WEI TSANG

  3. Loss Characteristics of The Internet

  4. Characteristics of Internet • 60-70% of paths do not show any loss • Those with loss have an average of 4.5 – 6% packet loss [Paxson97] End-to-end Internet packet dynamics NUS.SOC.CS5248 OOI WEI TSANG

  5. Packet Loss Pattern 1000 30 NUS.SOC.CS5248 OOI WEI TSANG

  6. Characteristic of Internet • Bursts of loss are typically short (2-3 consecutively loss packets) • Long burst do occur • Burst may occur periodically NUS.SOC.CS5248 OOI WEI TSANG

  7. Wireless Link • Loss rate measured in my office 10 ~ 20% • up to 50% reported! NUS.SOC.CS5248 OOI WEI TSANG

  8. General Error Recovery Techniques Perkins, Hodson and Hardman IEEE Network Magazine 1998

  9. Retransmission 1 2 3 4 3 1 2 4 3 NUS.SOC.CS5248 OOI WEI TSANG

  10. Redundant Data 1 2 2 3 3 4 4 5 1 2 2 3 3 4 5 NUS.SOC.CS5248 OOI WEI TSANG

  11. Error Concealment 1 2 3 4 1 2 4 NUS.SOC.CS5248 OOI WEI TSANG

  12. Retransmission for audio

  13. Retransmission is Bad • Need scalable feedback • NACK consumes bandwidth • May need to retransmit frequently • Retransmission maybe useless NUS.SOC.CS5248 OOI WEI TSANG

  14. Retransmission is Good • Only retransmit when needed • Exact recovery NUS.SOC.CS5248 OOI WEI TSANG

  15. Scalable Retransmission • On packet loss • T = random(0, RTT) • wait for T • multicast NACK • On receiving NACK from others • suppress own NACK NUS.SOC.CS5248 OOI WEI TSANG

  16. Retransmit when • group size is small • loss rate is low • large latency acceptable NUS.SOC.CS5248 OOI WEI TSANG

  17. Redundant Data for audio

  18. Parity FEC 1011001 XOR 1000010 0010010 0001001 NUS.SOC.CS5248 OOI WEI TSANG

  19. Parity FEC 1011001 1000010 0001001 0010010 NUS.SOC.CS5248 OOI WEI TSANG

  20. Parity FEC Ordering NUS.SOC.CS5248 OOI WEI TSANG

  21. Parity FEC Ordering NUS.SOC.CS5248 OOI WEI TSANG

  22. Parity FEC Ordering NUS.SOC.CS5248 OOI WEI TSANG

  23. Parity FEC Ordering NUS.SOC.CS5248 OOI WEI TSANG

  24. Parity FEC Ordering NUS.SOC.CS5248 OOI WEI TSANG

  25. Reed-Solomon Code • RS(n,k) RS NUS.SOC.CS5248 OOI WEI TSANG

  26. Reed-Solomon Code NUS.SOC.CS5248 OOI WEI TSANG

  27. Media Specific FEC 1 2 2 3 3 4 4 5 1 2 2 3 3 4 5 NUS.SOC.CS5248 OOI WEI TSANG

  28. Interleaving NUS.SOC.CS5248 OOI WEI TSANG

  29. Pro and Cons • Media Independent FEC • Overhead for redundant data • Exact recovery • Could be computationally costly • Media Specific FEC • Approximate recovery only NUS.SOC.CS5248 OOI WEI TSANG

  30. Error Concealment

  31. Effect of Loss on Audio • Speech • Human ears can interpolate • Loss up to length of phoneme can still be tolerable NUS.SOC.CS5248 OOI WEI TSANG

  32. Insertion-based Repair • Splice • Silence Substitution • Noise Substitution • Repetition NUS.SOC.CS5248 OOI WEI TSANG

  33. Other Repair Methods • Interpolation • Regeneration NUS.SOC.CS5248 OOI WEI TSANG

  34. Pro and Cons • Could be computationally costly • Approximate recovery only • Does not work well for long burst of packet loss NUS.SOC.CS5248 OOI WEI TSANG

  35. Colin’s Recommendations

  36. Non-Interactive Apps • Interleaving • FEC • Retransmission for unicast only NUS.SOC.CS5248 OOI WEI TSANG

  37. Interactive Applications • Media Specific FEC NUS.SOC.CS5248 OOI WEI TSANG

  38. Error Concealment • Repeat NUS.SOC.CS5248 OOI WEI TSANG

  39. Effects of Packet Loss on MPEG Jill Boyce and Robert Gaglianello ACM Multimedia 1998

  40. Measurement-based Study • Need to understand the problem before proposing solution NUS.SOC.CS5248 OOI WEI TSANG

  41. Data Gathering Method • From: NYC13 , Austin21, London18 • To: Holmdel, NJ NUS.SOC.CS5248 OOI WEI TSANG

  42. Data Gathering Method • Video: • Two 5-mins MPEG • 30 fps • 384 kbps and 1 Mbps • IBBPBBPBBPBBPBB • QSIF 176x112 and SIF 352x240 • One row per slice NUS.SOC.CS5248 OOI WEI TSANG

  43. Average Packet Loss NUS.SOC.CS5248 OOI WEI TSANG

  44. Packet Loss vs Time NUS.SOC.CS5248 OOI WEI TSANG

  45. How to Fill Packets • B 1 frame 1 packet • P 1 slice 1 packet • I 1 slice 1 packet NUS.SOC.CS5248 OOI WEI TSANG

  46. Packet Size Distributions NUS.SOC.CS5248 OOI WEI TSANG

  47. Packet Size vs Loss Rate NUS.SOC.CS5248 OOI WEI TSANG

  48. Lesson • 1 slice per packet even if larger than MTU • If smaller packets means higher loss rate: fill packet until MTU • Else one slice per MTU • Alt: Change size of slice NUS.SOC.CS5248 OOI WEI TSANG

  49. Frame Effected by Errors NUS.SOC.CS5248 OOI WEI TSANG

  50. Correlation of Packet Loss NUS.SOC.CS5248 OOI WEI TSANG

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