1 / 69

DOCSIS 3.0

DOCSIS 3.0. Rev.A00. Agenda & Discussion Points. CATV Market Dynamics DOCSIS 3 Overview DOCSIS 3 Benefits Preparing for DOCSIS 3 What you need to test How VeEX can help you Troubleshooting Summary Essential Technical Terms. Market Trends. Media Convergence.

ulema
Télécharger la présentation

DOCSIS 3.0

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. DOCSIS 3.0 Rev.A00

  2. Agenda & Discussion Points • CATV Market Dynamics • DOCSIS 3 Overview • DOCSIS 3 Benefits • Preparing for DOCSIS 3 • What you need to test • How VeEX can help you • Troubleshooting Summary • Essential Technical Terms Confidential & Proprietary Information of VeEX Inc.

  3. Market Trends • Media Convergence Source: Future services on HFC networks: 33th PIKE Conference, 14 October 2008, Zakopane, Poland Confidential & Proprietary Information of VeEX Inc.

  4. User Profiles & Applications Web 2.0 Digital Photos Home Networks Gaming Data & VoIP MP3 WMV VOD DVR/PVR DVD Blu-ray You Tube SDTV HDTV iPod Walkman Mobile Video Confidential & Proprietary Information of VeEX Inc.

  5. CATV Operators Need DOCSIS 3.0! Confidential & Proprietary Information of VeEX Inc.

  6. CATV Operators Feeling Pressure • Competition is extremely active • Telcos are deploying VDSL2, GPON, FIOS and FTTx (USA & Europe) • Consumer’s have an insatiable demand for new services • HDTV, VoD, PVR, interactive DTV etc • To meet the growing challenge cable operators have to: • Expand network capacity in cost effective and timely manner • Evolutionary steps - incremental investments in current technology • Revolutionary steps – need to decide if and when to implement a Next Generation HFC network Confidential & Proprietary Information of VeEX Inc.

  7. An Ongoing Battle for Customers • Verizon Beats Back Cable With YouTube Tilt • April 27, 2010 • Verizon Communications Inc. (NYSE: VZ) will soon use FiOS TV's ability to feed in thousands of YouTube videos as a key selling point in TV spots aimed at drawing cable and satellite TV subscribers to its completely fiber-fed platform. Confidential & Proprietary Information of VeEX Inc.

  8. DOCSIS OverviewDOCSIS 3.0 Benefits Confidential & Proprietary Information of VeEX Inc.

  9. DOCSIS Milestones Confidential & Proprietary Information of VeEX Inc.

  10. DOCSIS 3.0 Quick Overview Confidential & Proprietary Information of VeEX Inc.

  11. DOCSIS Throughput Compared • Notes: • Downstream bandwidths assuming QAM-256 modulation • Upstream bandwidth assuming QAM-64 modulation • Maximum synchronization speed and (Maximum usable speed) Confidential & Proprietary Information of VeEX Inc.

  12. DOCSIS 3.0 Channel Bonding Confidential & Proprietary Information of VeEX Inc.

  13. DOCSIS 3.0 Signals What do we know? • Physically the same as DOCSIS 2.0 signals • Consist of multiple QAM signals bonded logically together • Carry data of mutual relevance • Bonded channels can be contiguous or non-contiguous: • Contiguous - consist of frequency consecutive signals • Non-contiguous - interspersed in the spectrum with other carriers • MPEG-2 transport for downstream signals • QAM transport for upstream signals Confidential & Proprietary Information of VeEX Inc.

  14. DOCSIS 3.0 Preparation Confidential & Proprietary Information of VeEX Inc.

  15. Preparing for DOCSIS 3.0 Confidential & Proprietary Information of VeEX Inc.

  16. Obtaining the Required Bandwidth Confidential & Proprietary Information of VeEX Inc.

  17. Frequency Spectrum Changes Today 870MHz Soon 1GHz Confidential & Proprietary Information of VeEX Inc.

  18. Upstream Expansion How much gain? 250Mb/s 500Mb/s 1000Mb/s Confidential & Proprietary Information of VeEX Inc.

  19. Expanding HFC Network Capacity • Operators have strong differences in opinion with regard to options: • Solutions are typically driven by specific technical, geographical or local market factors • A combination of solutions often determines the preferred option Source: Michiel Peters, TNO - Benelux Chapter SCTE , 15 September 2008, Amsterdam Confidential & Proprietary Information of VeEX Inc.

  20. DOCSIS 3.0Plant Qualification & Test Methods Confidential & Proprietary Information of VeEX Inc.

  21. Typical DOCSIS Network Confidential & Proprietary Information of VeEX Inc.

  22. Plant Qualification Confidential & Proprietary Information of VeEX Inc.

  23. Upstream Test – Part 1 Setup • Configure the Upstream Generator (USG): • Frequency, level, modulation, bandwidth, and symbol rate • Transmit the QAM-64 signal upstream to a CX180+, CX350 or CX380 located in the Headend or Hub. Confidential & Proprietary Information of VeEX Inc.

  24. Upstream Test – Part 2 Basic • At the Headend or Hub, check: • Digital signal level (dBmV, dBµV) • Modulation Error Ratio (MER) Confidential & Proprietary Information of VeEX Inc.

  25. Upstream Test – Part 3 Spectrum • At the Headend or Hub, check: • Upstream spectrum (5-65MHz) for Ingress, CPD, and other interference • Check below 5MHz and above 65MHz all the way to 200MHz if possible • A QAM-64 signal requires a clean upstream path! Confidential & Proprietary Information of VeEX Inc.

  26. Still Having Problems? Level and MER look OK? • A Signal Level Meter (SLM) and Spectrum Analyzer are great application specific tools, but they can be limited in telling you everything you need to know about advanced digital signals • Downstream and upstream (DOCSIS) signals can be impaired by other factors not easily viewed using conventional test methods • Look for the “needle inside the QAM haystack” to figure out what is going on! Confidential & Proprietary Information of VeEX Inc.

  27. Upstream Testing – Part4 Advanced • For the Upstream, you need to check: • MER (equalized and un-equalized) • Pre and Post FEC • Frequency response (in-channel) • Group delay (in-channel) • Constellation diagram • Adaptive equalizer results Confidential & Proprietary Information of VeEX Inc.

  28. Downstream Testing – Part 5 Advanced • For the Downstream, you need to check: • Digital Power Level • MER (equalized and un-equalized) • Pre and Post FEC • Frequency response (in-channel) • Group delay (in-channel) • Constellation diagram • Adaptive equalizer results Confidential & Proprietary Information of VeEX Inc.

  29. Downstream QAM Parameters Constellation MER 64-QAM: 27 dB min 256-QAM: 31 dB min BER Pre/PostFEC • Pre/Post Errorred Seconds (PRES/POES) • The number of seconds with at least one corrected codeword • Severely Errorred Seconds • The number of seconds with at least one uncorrectable codeword Confidential & Proprietary Information of VeEX Inc.

  30. Impairments • Thermal noise is a basic physical phenomenon which cannot be avoided • Random voltage variation proportional to temperature, bandwidth and resistance. • At room temperature, in 6 MHz bandwidth and 75 ohms circuit, the thermal noise is approximately -60dBmV. After amplification, the noise level can get much higher. • All the other impairments are “human made”, they depend on the design, implementation and operation of all the elements in the signal chain • It is convenient to group all impairments into 2 categories: • Linear distortions and Non-linear distortions. Confidential & Proprietary Information of VeEX Inc.

  31. What Degrades MER? • Transmitted phase noise & Low carrier-to-noise ratio • Non-linear distortions (CTB, CSO, XMOD, CPD…) • Linear distortions (micro-reflections, amplitude ripple, group delay) • Severe impedance mismatches aka linear distortions • Improperly aligned or defective amplifiers • In-correct modulation profiles • Incorrect signal levels • In-channel ingress • Data collisions • Laser clipping Confidential & Proprietary Information of VeEX Inc.

  32. What MER is Acceptable? • Output of QAM Modulator – 40 dB • Input to Lasers – 39 dB • Output of Nodes – 37 dB • Output of Subscriber Taps – 35 dB • At the input to the subscriber’s receiver – 34 dB • The absolute minimum is 31db • MER is expressed in dB derived as follows: RMS error magnitude Average symbol magnitude 10 log Confidential & Proprietary Information of VeEX Inc.

  33. Downstream Performance Pre/Post FEC BER • What the results are telling you: • Level, MER and Constellation are OK • Pre/Post FEC BER indicate a problem • What to look for: • Interference from a sweep transmitter • Downstream laser clipping • Up-converter problem in the Headend • Loose connections or CPD Confidential & Proprietary Information of VeEX Inc.

  34. Notes on FEC • To have an accurate idea of the BER performance you need to know both pre and post FEC bit error rate • Forward error correction (FEC) is a digital error checking system that sends redundant information with the payload so the receiver can repair corrupted data and eliminate the need to retransmit. • By using the same Reed Solomon decoder at the receiving end, bit errors can be detected – these are called Pre-FEC errors • Pre FEC BER is the error rate of the incoming signal prior to being corrected by the FEC circuitry - a minimum of 1x10-7 is expected, but FEC may be able to correct errors as high as 1x10-6. • Post-FEC errors cause poor TV quality or DOCSIS data retransmission • Post FEC Bit errors are not acceptable and should be corrected • The FEC decoder needs a BER of >1x10-6 to operate properly • Both Pre and Post FEC BER need to be verified in order to determine if the FEC circuitry is working to correct errors and if so how hard. Confidential & Proprietary Information of VeEX Inc.

  35. QAM – Constellation Diagram Constellation Diagram Quadrant 4 Quadrant 1 Quadrant 3 Quadrant 2 Confidential & Proprietary Information of VeEX Inc.

  36. Q I Q I Modulation Error Ratio MER = 10log (avgsymbol power/avgerror power) Q A large “cloud” of symbol points means low MER—this is not good! Average error power Average symbol power A small “cloud” of symbol points means high MER—this is good! I Source: Hewlett-Packard Confidential & Proprietary Information of VeEX Inc.

  37. Forward Path Modulation QAM 64 or QAM 256 are most commonly used Confidential & Proprietary Information of VeEX Inc.

  38. Return Path Modulation – DOCSIS DOCSIS (Data-Over-Cable Service Interface Specifications) Reverse Path / Upstream Data Rate Standard symbol rate (bandwidth): 1.28 (1.6), 2.56 (3.2), 5.12 (6.4) MHz Confidential & Proprietary Information of VeEX Inc.

  39. Constellation Display • Learn to interpret the constellation display – it tells you a lot of the signal • Symbol points should be small and well-defined Confidential & Proprietary Information of VeEX Inc.

  40. The Adaptive Equalizer • Every MPEG2 digital receiver has an Adaptive Equalizer • The Equalizer typically cascades two digital filters: • Feed Forward Equalizer (FFE) - reference tap is the last of 16 taps • Decision Feedback Equalizer (DFE) - output is fed back to input, 108 taps long • Compensates for Linear distortions (Amplitude imperfections & group delay) • The Equalizer uses MER as a tool to adaptively cancel these Linear distortions Confidential & Proprietary Information of VeEX Inc.

  41. Adaptive Equalizer Test Functions Frequency Response & Group Delay Graphs Impairment Results Tap Expert Confidential & Proprietary Information of VeEX Inc.

  42. Linear Distortions – a closer look (1) What the key measurements are telling you! • Hum • Low frequency disturbances of the digital carrier e.g. switching power supplies • Phase Jitter • Instability of the QAM carrier seen at the demodulator • Phase changes of oscillators e.g. the up-converter • Introduces a back and forth rotation of the constellation where some symbols will eventually cross the decision boundaries and cause an error in transmission • EVM (Error Vector Magnitude) • A measure of how far constellation points deviate from their ideal locations. • Ratio of RMS Constellation Error Magnitude to peak Constellation symbol magnitude • Symbol Rate Error • Should be less than +/- 5pm Confidential & Proprietary Information of VeEX Inc.

  43. Linear Distortions – a closer look (2) • General Notes: • Amplitude and Group Delay responses help visualize the effects of filters, diplexers, traps, suck-outs in the signal path, from (and including) the QAM modulator up to the point of test. • The frequency span of the calculated responses is directly related to sampling period of the Equalizer Symbol period. For QAM-64, the span response is 5.05 MHz, while for QAM256 the span is 5.36 MHz What the measurement is telling you! • Frequency Response • Frequency response of the digital carrier • Micro-reflections can cause amplitude ripple in the frequency response • Should be less than 3dB (peak-to-peak) • Group Delay • Different frequencies travel through the same medium at different speeds (see supporting slide) • Worse near band edges and diplex filter roll-off areas • Group Delay variation is usually expressed in ns for the Downstream and in “ns / MHz” for the Upstream • Should be < 50ns peak-to-peak Confidential & Proprietary Information of VeEX Inc.

  44. Linear Distortions – a closer look (3) What the measurement is telling you! • Echo Margin • Echoes are micro-reflections • The tallest vertical bar is the incident signal (reference tap) • Smallest difference between any coefficient and the DOCSIS template defined by CableLabs • Safety margin when getting too close to the “cliff effect” • Shouldideally be > 6dB • Equalizer Stress • Derived from all the Equalizer coefficients • Indicates how hard the Equalizer is working to cancel out the Linear distortions • Global indicator (the higher the figure, the less stress) • Noise Margin • Generally, the lower the MER, the larger the probability of errors in transmission (Pre-FEC and Post FEC) • Amount of noise that can safely be added to degrade the Equalized MER before losing the signal (cliff effect) Confidential & Proprietary Information of VeEX Inc.

  45. Linear Distortions Micro-reflection at about 2.5 µs (2500 ns): Assume ~1 ns per ft., 2500/2 = 1250 ft (actual is 1.17 ns per ft: (2500/1.17)/2 = 1068 ft) Frequency response ripple ~400 kHz p-p: Distance to fault = 492 x (.87/.400) = 1070 ft. Confidential & Proprietary Information of VeEX Inc.

  46. Operational RF Levels • DOCSIS recommends that the digitally modulated signal’s average power level be set 6 dB to 10 dB below what the visual carrier level of an analog TV channel on the same frequency would be • This ratio should be maintained throughout the entire cable network Confidential & Proprietary Information of VeEX Inc.

  47. DOCSIS 3.0 CM Emulation Link Up Step-by-step CM link up process to clearly identify any failed steps After link up, power level on forward and return paths are measured. Confidential & Proprietary Information of VeEX Inc.

  48. DOCSIS 3.0 CM – IP Tests (1) Complete server connection status indicates any IP problems Once the CM is on-line, a full range of IP tests including Ping test can be performed Confidential & Proprietary Information of VeEX Inc.

  49. DOCSIS 3.0 CM – IP Tests (2) Throughput (FTP) Download and Upload should be verified at the CM service location. Web Test and Web Browser provide bandwidth and visual indications of performance Confidential & Proprietary Information of VeEX Inc.

  50. DOCSIS 3.0 CM – VoIP Tests (1) VoIP Expert generates industry standard wave files to verify MOS and R-Factor of upstream and downstream and includes packet jitter, packet loss, and delay. Real-time of subjective voice quality evaluation (MOS and R-factor) using the Telchemy Algorithm and test method is provided Confidential & Proprietary Information of VeEX Inc.

More Related