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DSL Troubleshooting: Intermittent Faults CommTech 14 May 2009 Jim Wahl  Aware, Inc.
Agenda <ul><li>Identifying Intermittent Troubles </li></ul><ul><ul><li>Lines change </li></ul></ul><ul><ul><li>Stability m...
Aware Inc. <ul><li>Background </li></ul><ul><ul><li>1986: Biometrics and Image Compression Products </li></ul></ul><ul><ul...
DSL and Data Rate <ul><li>DSL data rate is based on the &quot;space&quot; between the signal attenuation and the noise flo...
Loop Length and SNR / Data Rate   7,000ft loop 6,000ft loop
Noise and SNR / Data Rate
Intermittent DSL Troubles <ul><li>Changes in crosstalk levels: </li></ul>
Count of Impulses per Hour Moderate to low amount of impulses throughout the night
Count of Impulses per Hour Very quiet in early morning hours with large jump beginning at 5am and lasting until 8am.
Count of Impulses per Hour Moderate level of impulses with three highest totals at 3am, 7am, 11am
What’s a “bad” DSL line? <ul><li>Depends on service. …   </li></ul><ul><ul><li>High-speed internet service vs anything els...
What’s a “bad” DSL line? <ul><li>One that a generates poor customer experience.  </li></ul><ul><li>If a customer hasn’t co...
Key Stability Metrics <ul><li>MTBE (Mean Time Between Error)   </li></ul><ul><ul><li>Average time between two CRCs (or Cod...
Where do I get them?  <ul><li>Not Test Equipment   </li></ul><ul><ul><li>Stability metrics are collected over time.  </li>...
Troubleshooting Faults
Sources of Intermittent Faults <ul><li>Impulse noise </li></ul><ul><li>External or in-home  </li></ul><ul><li>ADSL Crossta...
Impulse Noise
Impulse Noise <ul><li>Problems it causes: </li></ul><ul><ul><li>Video pixelization </li></ul></ul><ul><ul><li>Audio hiccup...
Possible Solutions <ul><li>Moving the modem away from suspected interference sources </li></ul><ul><ul><li>Problems: </li>...
Impulse Monitoring Sample #1 QLN
Impulse Monitoring Impulse Sample #1 Detected Impulse Lasts about 50 microseconds Peaks at more than 6mV
Impulse Monitoring Impulse Sample #2 Impulse affects a large portion of the ADSL2 spectrum QLN
Impulse Monitoring Impulse Sample #2 Impulse
Impulse Monitoring Impulse Sample #3 An impulse affecting the beginning and middle of the ADSL 1 band QLN
Impulse Monitoring Impulse Sample #3 Brief impulse
Impulse Monitoring Impulse Sample #4 Affects a large area of the spectrum QLN
Impulse Monitoring Impulse Sample #4 Powerful, yet brief, impulse
Impulse Monitoring Impulse Sample #5 Frequency Domain
Impulse Monitoring Impulse Sample #5 Impossible to see beginning or end in time domain.
Troubleshooting Impulses <ul><li>Voice-based Methods Limited </li></ul><ul><ul><li>Magnitude, duration, threshold counters...
Wideband Noise
Characterizing Noise <ul><li>Frequency Span </li></ul><ul><ul><li>How broad is disturber (T1 vs AM)  </li></ul></ul><ul><l...
Characterizing Noise
Characterizing Noise Low Varies greatly  Rapid  Varies greatly  Micro-cuts, resistive faults, corroded splices  Low Modera...
Mitigating Noise <ul><li>Error Correction  </li></ul><ul><ul><li>INP, PHY-R, Delay </li></ul></ul><ul><li>Optimized Margin...
Mitigation Tools
Takeaways <ul><li>DSL Lines Vary </li></ul><ul><ul><li>Time of day, day of year. </li></ul></ul><ul><ul><li>Stability metr...
Jim Wahl Aware, Inc. www.aware.com [email_address]
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  1. 1. DSL Troubleshooting: Intermittent Faults CommTech 14 May 2009 Jim Wahl Aware, Inc.
  2. 2. Agenda <ul><li>Identifying Intermittent Troubles </li></ul><ul><ul><li>Lines change </li></ul></ul><ul><ul><li>Stability metrics </li></ul></ul><ul><li>Troubleshooting Impulse Noise </li></ul><ul><ul><li>Do I really have an impulse noise problem? </li></ul></ul><ul><ul><li>What can I do about it? </li></ul></ul><ul><li>Troubleshooting Other Noise </li></ul><ul><ul><li>DSLAM-based noise mitigation techniques? </li></ul></ul><ul><ul><li>When is dispatch-required? </li></ul></ul>
  3. 3. Aware Inc. <ul><li>Background </li></ul><ul><ul><li>1986: Biometrics and Image Compression Products </li></ul></ul><ul><ul><ul><li>Fingerprint compression, facial imaging OEM products </li></ul></ul></ul><ul><ul><li>1993: DSL Intellectual Property Licensing </li></ul></ul><ul><ul><ul><li>Silicon customers: Infineon, Ikanos/ADI </li></ul></ul></ul><ul><ul><li>2002: Test and Diagnostics Products </li></ul></ul><ul><ul><ul><li>Hardware and Dr. DSL diagnostics software </li></ul></ul></ul><ul><li>Products </li></ul><ul><ul><li>Test Equipment OEM: </li></ul></ul><ul><ul><ul><li>UDMT (ADSL2/VDSL2 CO/RT) modem modules </li></ul></ul></ul><ul><ul><ul><li>with Dr. DSL diagnostics </li></ul></ul></ul><ul><ul><li>Dr. DSL Line Diagnostics Platform </li></ul></ul><ul><ul><li>Technician Dr. DSL </li></ul></ul><ul><li>Diagnostics Customers </li></ul><ul><ul><li>TELUS, Spirent, Tollgrade, 3M, JDSU, Fluke, Sunrise, Occam, Alcatel, and many others. </li></ul></ul>Bedford, MA Corporate Office
  4. 4. DSL and Data Rate <ul><li>DSL data rate is based on the &quot;space&quot; between the signal attenuation and the noise floor. </li></ul><ul><li>This is the signal-to-noise ratio (SNR). </li></ul><ul><li>The greater the area between the signal and noise floor, the higher the SNR, and the higher data rate. </li></ul>
  5. 5. Loop Length and SNR / Data Rate 7,000ft loop 6,000ft loop
  6. 6. Noise and SNR / Data Rate
  7. 7. Intermittent DSL Troubles <ul><li>Changes in crosstalk levels: </li></ul>
  8. 8. Count of Impulses per Hour Moderate to low amount of impulses throughout the night
  9. 9. Count of Impulses per Hour Very quiet in early morning hours with large jump beginning at 5am and lasting until 8am.
  10. 10. Count of Impulses per Hour Moderate level of impulses with three highest totals at 3am, 7am, 11am
  11. 11. What’s a “bad” DSL line? <ul><li>Depends on service. … </li></ul><ul><ul><li>High-speed internet service vs anything else. </li></ul></ul><ul><ul><li>IPTV dramatically increases error-free QoS requirement. </li></ul></ul><ul><ul><li>VoIP increases low-latency QoS requirement. </li></ul></ul><ul><li>PHY-layer IPTV Benchmarks </li></ul><ul><ul><li>Example 1: < 1 resync / week; 1 CRC / hour. </li></ul></ul><ul><ul><li>Example 2: < 1 resync / day; 1 CRC / 4hrs. </li></ul></ul><ul><ul><li>BBF WT-126: < 1 CRC / 30 min for SD; < 1 CRC / 4hrs for HD. </li></ul></ul><ul><li>Why the Discrepancy? </li></ul><ul><ul><li>“ QoE” dependent on many factors, including content and compression ratios. </li></ul></ul><ul><ul><li>PHY-layer errors can be corrected or mitigated at higher layer. </li></ul></ul><ul><ul><li>Some packets (I- and P-frames) more important than others (B-frames). </li></ul></ul>
  12. 12. What’s a “bad” DSL line? <ul><li>One that a generates poor customer experience. </li></ul><ul><li>If a customer hasn’t complained, yet. … </li></ul><ul><ul><li>Identify lines that are likely to generate complaints. </li></ul></ul><ul><ul><li>To identify these lines, we need metrics. </li></ul></ul><ul><li>If a customer is already complaining. </li></ul><ul><ul><li>Improve service. </li></ul></ul><ul><ul><li>To measure improvements, we need metrics. </li></ul></ul>
  13. 13. Key Stability Metrics <ul><li>MTBE (Mean Time Between Error) </li></ul><ul><ul><li>Average time between two CRCs (or Code Violations). </li></ul></ul><ul><ul><li>Expressed in seconds or bits. </li></ul></ul><ul><li>MTBR (Mean Time Between Resyncs) </li></ul><ul><ul><li>Average time between resyncs. </li></ul></ul><ul><ul><li>Excludes user-generated events (diagnostic test, consumer powering off modem, …). </li></ul></ul><ul><li>BAT-V (Bit Allocation Table Variation) </li></ul><ul><ul><li>Average number of minor and major “bit-swap” events. </li></ul></ul><ul><ul><li>A general metric for how much the underlying physical layer is changing—more coming. … </li></ul></ul>All of the above metrics are calculated non-intrusively.
  14. 14. Where do I get them? <ul><li>Not Test Equipment </li></ul><ul><ul><li>Stability metrics are collected over time. </li></ul></ul><ul><ul><li>Test equipment provides snapshots. </li></ul></ul><ul><li>DSLAM? </li></ul><ul><ul><li>Partly. </li></ul></ul><ul><ul><li>DSLAMs have the raw data, but not the analysis. </li></ul></ul><ul><li>Analysis Tools </li></ul><ul><ul><li>Collect data from multiple DSLAMs. </li></ul></ul><ul><ul><li>Normalize and calculate metrics. </li></ul></ul><ul><ul><li>Compare to other lines in node, neighborhood, network. </li></ul></ul><ul><ul><li>Categorize : 1) DLM, 2) Dispatch, 3) Downgrade, 4) Upgrade </li></ul></ul>
  15. 15. Troubleshooting Faults
  16. 16. Sources of Intermittent Faults <ul><li>Impulse noise </li></ul><ul><li>External or in-home </li></ul><ul><li>ADSL Crosstalk </li></ul><ul><li>T1 Crosstalk </li></ul><ul><li>AM Radio (RFI) </li></ul>1 1 2 2 3 3 4 4 <ul><li>Corroded splice </li></ul><ul><li>Resistive fault </li></ul>4
  17. 17. Impulse Noise
  18. 18. Impulse Noise <ul><li>Problems it causes: </li></ul><ul><ul><li>Video pixelization </li></ul></ul><ul><ul><li>Audio hiccups </li></ul></ul><ul><li>Possible sources: </li></ul><ul><ul><li>Rotary tools </li></ul></ul><ul><ul><ul><li>Drills, power sanders </li></ul></ul></ul><ul><ul><li>Household appliances with motors </li></ul></ul><ul><ul><ul><li>Electric toothbrushes, older printers, garage door openers, older refrigerators, sewing machines. </li></ul></ul></ul><ul><ul><li>Outdoor heavy equipment </li></ul></ul><ul><ul><ul><li>Construction machinery </li></ul></ul></ul>
  19. 19. Possible Solutions <ul><li>Moving the modem away from suspected interference sources </li></ul><ul><ul><li>Problems: </li></ul></ul><ul><ul><ul><li>Not always possible to relocate modem </li></ul></ul></ul><ul><ul><ul><li>Interference may permeate throughout location </li></ul></ul></ul><ul><li>Error Correction (INP, PHY-R, Delay) </li></ul><ul><ul><li>Problems: </li></ul></ul><ul><ul><ul><li>Introduces latency </li></ul></ul></ul><ul><ul><ul><li>Adds overhead data, reducing core line data rate </li></ul></ul></ul><ul><ul><ul><li>Often trial-and-error in the DSLAM profile. </li></ul></ul></ul>
  20. 20. Impulse Monitoring Sample #1 QLN
  21. 21. Impulse Monitoring Impulse Sample #1 Detected Impulse Lasts about 50 microseconds Peaks at more than 6mV
  22. 22. Impulse Monitoring Impulse Sample #2 Impulse affects a large portion of the ADSL2 spectrum QLN
  23. 23. Impulse Monitoring Impulse Sample #2 Impulse
  24. 24. Impulse Monitoring Impulse Sample #3 An impulse affecting the beginning and middle of the ADSL 1 band QLN
  25. 25. Impulse Monitoring Impulse Sample #3 Brief impulse
  26. 26. Impulse Monitoring Impulse Sample #4 Affects a large area of the spectrum QLN
  27. 27. Impulse Monitoring Impulse Sample #4 Powerful, yet brief, impulse
  28. 28. Impulse Monitoring Impulse Sample #5 Frequency Domain
  29. 29. Impulse Monitoring Impulse Sample #5 Impossible to see beginning or end in time domain.
  30. 30. Troubleshooting Impulses <ul><li>Voice-based Methods Limited </li></ul><ul><ul><li>Magnitude, duration, threshold counters miss important events. </li></ul></ul><ul><ul><li>Not usually clear how to set thresholds. </li></ul></ul><ul><li>Auto-thresholds, Frequency Domain </li></ul><ul><ul><li>Set thresholds at levels likely to impact DSL service. </li></ul></ul><ul><ul><li>Time + frequency domain provide more insight into types of events. </li></ul></ul><ul><li>Auto-analysis, Identification </li></ul><ul><ul><li>Recommend whether DSLAM profile can correct for impulse events. </li></ul></ul><ul><ul><li>Characterize impulses to help segment / troubleshoot. </li></ul></ul>Measuring improvements?
  31. 31. Wideband Noise
  32. 32. Characterizing Noise <ul><li>Frequency Span </li></ul><ul><ul><li>How broad is disturber (T1 vs AM) </li></ul></ul><ul><li>Rise Time </li></ul><ul><ul><li>How quickly does noise appear. </li></ul></ul><ul><li>Magnitude </li></ul><ul><li>Coincident PSD </li></ul><ul><ul><li>How many different shapes are present at the same time. </li></ul></ul>
  33. 33. Characterizing Noise
  34. 34. Characterizing Noise Low Varies greatly Rapid Varies greatly Micro-cuts, resistive faults, corroded splices Low Moderate Rapid Narrow Other RFI Moderate Moderate Moderate Narrow AM Radio Frequency Interference (RFI) Low High Rapid Very narrow Impulse Noise Low Low to Mod <ul><li>Slow: service penetration </li></ul><ul><li>Moderate: capacitive coupling due to environmental factors </li></ul><ul><li>Rapid: near-by service &quot;flipped on&quot; </li></ul>Wide Crosstalk Coincident PSD Magnitude Rise Time Frequency Span Type
  35. 35. Mitigating Noise <ul><li>Error Correction </li></ul><ul><ul><li>INP, PHY-R, Delay </li></ul></ul><ul><li>Optimized Margin and Bit-swapping </li></ul><ul><li>Artificial Noise / Virtual Noise </li></ul><ul><li>Transmit PSD Masks </li></ul>Each has advantages / disadvantages and equipment dependencies.
  36. 36. Mitigation Tools
  37. 37. Takeaways <ul><li>DSL Lines Vary </li></ul><ul><ul><li>Time of day, day of year. </li></ul></ul><ul><ul><li>Stability metrics key for tracking performance. </li></ul></ul><ul><li>Two General Types of Disturbers </li></ul><ul><ul><li>Impulsive – troubleshoot with handhelds. </li></ul></ul><ul><ul><li>RFI, crosstalk – troubleshoot with centralized tools. </li></ul></ul><ul><li>Remedy </li></ul><ul><ul><li>Impulse-free lines impossible, but minimize below DSL impact. </li></ul></ul><ul><ul><li>Advanced DSLAM profiles protect against changes in RFI, crosstalk noise sources. </li></ul></ul>
  38. 38. Jim Wahl Aware, Inc. www.aware.com [email_address]

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