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Error Recovery

Error Recovery. Problems with Internet. Limited Bandwidth Varying Conditions Delay Jitter Packet Loss Delay Heterogeneity :. You Are Here. Encoder. Decoder. Middlebox. Receiver. Sender. Network. Overview. Characteristics of the Internet General techniques

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Error Recovery

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  1. Error Recovery

  2. Problems with Internet • Limited Bandwidth • Varying Conditions • Delay Jitter • Packet Loss • Delay • Heterogeneity :

  3. You Are Here Encoder Decoder Middlebox Receiver Sender Network

  4. Overview • Characteristics of the Internet • General techniques • Error recovery for audio • Effect of loss on MPEG • Error recovery for MPEG

  5. Loss Characteristics of The Internet

  6. 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

  7. Packet Loss Pattern Number of Occurrences 1000 Burst Length 30

  8. Characteristics of Internet • Bursts of loss are typically short (2-3 consecutively loss packets) • Long burst do occur • Burst may occur periodically

  9. Wireless Link • Loss rate measured in my office 10 ~ 20% • up to 50% reported!

  10. Gilbert Model GOOD BAD

  11. A Survey of Packet-Loss Recovery Techniques for Streaming Audio Perkins, Hodson and Hardman IEEE Network Magazine 1998

  12. Retransmission 1 2 3 4 3 X 1 2 4 3

  13. Redundant Data 1 2 2 3 3 4 4 5 1 2 2 3 3 4 5

  14. Error Concealment 1 2 3 4 1 2 4

  15. Retransmission for audio

  16. Pros/Cons of Retransmissions

  17. Scalable Retransmission • On packet loss • T = random(0, RTT) • wait for T • multicast NACK • On receiving NACK from others • suppress own NACK

  18. Retransmit when • Group size is small • Loss rate is low • Large latency acceptable

  19. Selective Retransmission • Retransmission based on priority of packets • Important/urgent packets are retransmitted first

  20. Redundant Data for audio

  21. ParityForward Error Correction 1011001 XOR 1000010 0010010 0001001

  22. Parity Forward Error Correction 1011001 1000010 0001001 0010010

  23. Parity FEC Ordering

  24. Parity FEC Ordering

  25. Parity FEC Ordering

  26. Parity FEC Ordering

  27. Parity FEC Ordering

  28. Reed-Solomon Code • RS(n,k) RS n k

  29. Reed-Solomon Code

  30. Media Specific FEC 1 2 2 3 3 4 4 5 1 2 2 3 3 4 5

  31. Pros/Cons of Redundant Data

  32. Interleaving

  33. Pros/Cons of Interleaving

  34. Error Concealment

  35. Effect of Loss on Audio • Speech • Human ears can interpolate • Loss up to length of phoneme can still be tolerable

  36. Insertion-based Repair • Splice • Silence Substitution • Noise Substitution • Repetition

  37. Other Repair Methods • Interpolation • Regeneration

  38. Colin’s Recommendations

  39. Non-Interactive Apps • Interleaving • FEC • Retransmission for unicast only

  40. Interactive Applications • Media Specific FEC

  41. Error Concealment • Repeat

  42. Packet Loss Effects on MPEG Video Sent over the Public Internet Jill Boyce and Robert Gaglianello ACM Multimedia 1998

  43. Measurement-based Study • Need to understand the problem before proposing solution

  44. Data Gathering Method • From: NYC13 , Austin21, London18 • To: Holmdel, NJ

  45. 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

  46. Average Packet Loss

  47. Frame Effected by Errors % Frames in Error Packet Loss Rate

  48. Overview of Error Recovery for Video

  49. Methods • Retransmission • Interleaving • Error Concealment • FEC • Limiting Error Propagation • Reference Frame Selection

  50. Reference Frame Selection I P B B P I X

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