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Sunrise Telecom Presents: Cable 101 Sales Training – CATV Products

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Presentation on theme: "Sunrise Telecom Presents: Cable 101 Sales Training – CATV Products"— Presentation transcript:

1 Sunrise Telecom Presents: Cable 101 Sales Training – CATV Products
By: Jerry Green March 2010 Proprietary & Confidential

2 Proprietary & Confidential
Agenda In the beginning…… System Architectures Signal on the Network Channel Allocations Analog Channels Digital Channels System Sweep DOCSIS Future March 2010 Proprietary & Confidential

3 Proprietary & Confidential
It all began….. 1948 – John Walson of Pennsylvania installs an antenna on the mountain and runs twin-lead wires to his appliance store. TV sales soared. John began to connect customers to his antenna & changes the wire to coaxial cable to improve picture quality. Ed Parson, of Astoria, Oregon built a CATV system consisting of twin-lead strung from housetop to house top. 1950 – Bob Tarlton, of Lansford Pennsylvania used coaxial cable on utility polls under a franchise from the city. Community Antenna Television (CATV) was born. March 2010 Proprietary & Confidential

4 First Network Architecture
System components: Preamp installed at antenna Maybe a ‘booster’ in the tree 300 ohm ‘Railroad Track’ wire Number of channels: 1 to 10 Performance: OK to poor March 2010 Proprietary & Confidential

5 Test Equipment of the 1950’s & 60’s
Jerrold 704 Developed 1951 Manufactured from 1952 to 1967 Jerrold 727 Developed 1966 Manufactured from 1967 to mid 70’s Portable TV Measure levels with modified unit See distortions March 2010 Proprietary & Confidential

6 Tapped Trunk Architecture
Unity Gain Headend March 2010 Proprietary & Confidential

7 Trunk/Bridger Architecture
Antenna Tower Headend TV Transmitter Typical amplifier cascades: 35+ amplifiers. March 2010 Proprietary & Confidential

8 Trunk/Bridger Architecture with Return
March 2010 Proprietary & Confidential

9 Proprietary & Confidential
Microwave Transport March 2010 Proprietary & Confidential

10 Hybrid Fiber Coax (HFC) Architecture
Fiber Link Fiber Link reduces the number of amplifiers in cascade March 2010 Proprietary & Confidential

11 Broadband networks HFC architectures
Hybrid Fiber-Coaxial Network Infrastructure March 2010 Proprietary & Confidential

12 What is the Forward Path of the System
Return Equip. R H L Forward Signal Path Signal flow in the forward path is from the headend to the customers home as indicated by the blue arrows. Each amplifier compensates for the loss in the wire before the amplifier under test. In the forward path, signals originate at the headend and are transmitted to many customer drops. One output feeds many inputs. In the forward system the outputs of like devices are typically set to same output level. Each amplifier compensates for the cable and passive loss before it. This principal (Gain = Loss) is Unity Gain. Level changes in the forward path occur due to changes in cable loss caused by temperature. Automatic level or gain controls (ALC or AGC) are located in the amplifiers. A section of the alignment procedure for the forward path involves setting the operating point for the automatic control circuit. This procedure include measuring the absolute level of the pilot channels used in the system and comparing the levels to the calculated levels for the current temperature. If the pilot frequencies are entered into the sweep table as measured frequencies, the automatic control system can be adjusted in the normalized sweep mode eliminating the need to change measurement modes. March 2010 Proprietary & Confidential

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Sample Amplifier Forward Path H L Slope Control Response Equalizer AGC / ASC Forward Amplifier Return Amplifier Bridger Amplifier T.P. -20 dB March 2010 Proprietary & Confidential

14 Proprietary & Confidential
What is the Return Path Return Signal Path H L R R Return Equip. Each amplifier compensates for the loss in the wire after the amplifier under test. In the return path, signals originate at the customer drops and are transmitted back to the headend. Many outputs feeding one input. Each amplifier compensates for the cable and passive loss after the return amplifier. This is the same physical cable the forward amplifier is compensating for at a given location. In the return path, devices are adjusted for a consistent input level at the next device. This make testing more difficult because the measurement or common reference point is some distance from adjustment point. To accomplish the task the technician needs a method of making a measurement at one location and viewing measurements from a different location. The 3010H/R performs this function. Level changes in the return path are also effected by temperature as in the forward path, however the largest contributor to return level changes is the placement of the equipment and differences in the passive loss between the equipment and the amplifier. In order to control the output level of devices installed in the system, the data receiver installed at the headend monitors the receive levels from each device and adjusts the levels automatically. The balancing of the return path is critical for this system to operate correctly. Signal flow in the return path is from the customers home to the headend as shown by the blue arrows. March 2010 Proprietary & Confidential

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Sample Amplifier Return Path H L Slope Control Response Equalizer AGC / ASC Forward Amplifier Return Amplifier Bridger Amplifier T.P. -20 dB March 2010 Proprietary & Confidential

16 Proprietary & Confidential
Signals on the Network March 2010 Proprietary & Confidential

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Channel Types & Terms Analog NTSC, PAL, SECAM Digital 64QAM, 256QAM, 8VSB Annex A, Annex B, Annex C DOCSIS, EuroDOCSIS March 2010 Proprietary & Confidential

18 Digital Channel Penetration
Evolution of digital signals penetration in HFC transport architecture 2000 90 % analog TV 10% digital TV 2005 60 % analog TV 40% digital TV 2008 25 % analog TV 75% digital TV 2012 0 % analog TV 100% digital TV March 2010 Proprietary & Confidential

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Why change to Digital? Bandwidth efficiency allows more program channels Picture quality improvement Better conditional access system Supports HDTV Not content dependent March 2010 Proprietary & Confidential

20 PAL Cable Frequency Allocation
March 2010 Proprietary & Confidential

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Channel Plan March 2010 Proprietary & Confidential

22 Analog TV Standard Spectrum
March 2010 Proprietary & Confidential

23 Analog TV, NTSC / PAL / Secam / HDTV
Lines/Image 525 625 Images/second 30 25 Horizontal Frequency kHz kHz Vertical Frequency 59.94 Hz 50 Hz High Definition Television (HDTV) 16:9 Format (widescreen) March 2010 Proprietary & Confidential

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Spectrum Analysis Ch. 3 Spectrum Analysis Ch. Allocation 6 MHz V/A 4.5 MHz V/Color 3.58 MHz Lower Band Edge MHz Video Carrier MHz Audio Carrier MHz Lower Band Edge MHz March 2010 Proprietary & Confidential

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VITS Signals 525 LINES Horizontal Blanking SCAN MOTION Vertical Blanking Receiver Frame (Raster) 485 Vertical Sync March 2010 Proprietary & Confidential

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Analog Channel in Time March 2010 Proprietary & Confidential

27 Analog TV, TV Signal Modulation
March 2010 Proprietary & Confidential

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Analog TV, test signal Basic video reference points, - Sync tip amplitude, - Depth of modulation - Color Burst Test signals are added to measure signal quality - Vertical synchronisation - Lines 7 to 21 are part of the non-visible image March 2010 Proprietary & Confidential

29 Proprietary & Confidential
Analog TV Chroma Chroma (or Color) Subcarrier 3.58MHz Suppressed carrier, AM modulation March 2010 Proprietary & Confidential

30 Analog TV audio transmissions
Frequency modulated audio sub-carrier 4.5 MHz to 5.5 MHz, ± 25 kHz Pre-emphasis Reduces high frequency transmission noise Amplification of high frequencies before modulation An inverse filter is applied after demodulation Encoding similar to FM stereo receivers L+R base signal L-R differential signal March 2010 Proprietary & Confidential

31 Proprietary & Confidential
Analog Measurements Levels Carrier Frequency Carrier to Noise (CCN) Coherent Disturbances (CCN, CSO & CTB) HUM In-Channel Response Color Measurements March 2010 Proprietary & Confidential

32 Analog Measurements Carrier Levels
March 2010 Proprietary & Confidential

33 Proprietary & Confidential
Absolute and Relative Absolute Frequency, Hz Relative Amplitude in dB Absolute Amplitude, dBmV Absolute levels and frequency only on visual carrier All other amplitudes and frequencies are relative to the visual carrier Relative Frequency, Hz March 2010 Proprietary & Confidential

34 Proprietary & Confidential
CM2000/2800 SLM Mode March 2010 Proprietary & Confidential

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Multi-Channel Modes Mini Scan Scan March 2010 Proprietary & Confidential

36 AT2500 Channel Level Display
March 2010 Proprietary & Confidential

37 CATV Measurements Carrier to Noise (CCN)
March 2010 Proprietary & Confidential

38 Proprietary & Confidential
Carrier to Noise Ratio Overload (TP) Dynamic Range CCN In order to accurately measure CNR we must meet 2 conditions. The analyzer has to have enough signal so that the noise of the system is above the level of the spectrum analyzer’s noise floor. The analyzer also requires that the total power is below it’s overload point. To get higher signal, use a pre-amplifier. To limit the total power, use a bandpass filter. The difference in dB between the overload point and the Spectrum Analyzer’s noise floor is called the dynamic range. S.A. Noise Floor March 2010 Proprietary & Confidential

39 CCN Measurement Algorithm
Measure Carrier Level Measure Noise in a 30KHz Bandwidth Correct for: Bandwidth of noise to 4 MHz (add dB) Log Detection (add 2.5 dB) Bandpass Filter Shape (subtract .5 dB) Correct for Noise to near Noise Correct for pre-amplifier if used Subtract corrected noise from carrier level Thankfully modern day analyzers perform these computations automatically. March 2010 Proprietary & Confidential

40 Out of Band CCN Measurement
Carrier Level NOTE: Noise measurement most be corrected for video bandwidth & instrument measurement errors. An out of band CNR measurement measures the carrier, then measures the noise between it and the lower adjacent sound carrier. This measurement is good for an idea of the carrier to noise, but is not accurate. It is also an in-service measurement. It is not a valid measurement for FCC proofs because they require the measurement to be made within the bandwidth of the channel. Noise Measurement March 2010 Proprietary & Confidential

41 Setup Out-of-Band CCN Measurement
Center frequency = Video carrier frequency ==> SINGLE ==> COMBINED OR ==> IN-CH GATED Before actually initiating a test there are some procedures that need to be followed. It is highly recommended that a Bandpass filter be used when making performance measurements with any spectrum analyzer. The function keys on the right hand side of the AT2000RQ allow the user to determine how the test will be performed. The F1 key toggles the unit between single and combined. When in single test mode, only the measurement indicated by the F2 softkey will be made The F2 choices are C/N, CSO and CTB. The F3 key determines whether this will be an in-channel (manual) method or a gated measurement method. Manual measurements of CSO and CNR require removal of either the video modulation or the video carrier itself from the system temporarily while the measurement is being made. The manual measurement of CTB requires that the video carrier be removed from the system. CTB cannot be measured by removing only the video modulation because the CTB in most cable system falls directly on the video carrier frequency. We will look a little closer at this when we examine a typical results screen. While manual mode is an acceptable way of making these measurements, it is intrusive and requires either the ability to turn the carrier off remotely or the assistance of a second person to turn the carrier off manually. For these reasons, the gated measurement was developed. The gated measurement involves timing the CNR, CSO and CTB measurements to the incoming video signal. For CSO and CNR measurements it is possible to make gated measurements during a quiet line in the video signal without any external equipment on the headend modulator. CTB can also be measured during a quiet line of video, but requires a smart switch that will turn off the carrier itself during a chosen quiet line. A quiet line of video provides about 50 uSec of “no modulation” on the video carrier. For the AT2000Q, this is plenty of time to be able to make the CNR, CTB and CSO measurements. The AT2000RQ requires only 40 uSec per frame to make the measurements. The significance of this is that other analyzers on the market require 80 uSec per frame in order to be able to make an accurate measurement. Therefore, the same line in both fields must be used and in the case of CTB the carrier is turned off twice as many times per frame. On some television sets you will hear a slight popping noise when the carrier is being turned off for the 40 uSec interval. However, this faint popping noise becomes more objectionable to the customer as the frequency of it increases. Test equipment requiring 80 uSec per frame switching needs to have the carrier switched off twice as often and the resulting interference is higher in pitch and noticeably more objectionable. F4 asks whether or not you are using an external Bandpass filter on the unit while making this test. As discussed earlier, Bandpass filters are a good idea when making performance measurements with a spectrum analyzer because they prevent the front end of the analyzers from overloading. When F4 is set to YES, at AT2000RQ will be able to use less attenuation on the front end of the unit bringing it’s full dynamic range into play when making the C/N measurement. F5 will take the user to the measurement parameter setup screen. PRESS F5 NEXT SLIDE Noise Meas set to clear area Press F5 to setup Measurement parameters. March 2010 Proprietary & Confidential

42 Out-of-Band CCN Measurement
March 2010 Proprietary & Confidential

43 Out-of-Band CCN Measurement
Before actually initiating a test there are some procedures that need to be followed. It is highly recommended that a Bandpass filter be used when making performance measurements with any spectrum analyzer. The function keys on the right hand side of the AT2000RQ allow the user to determine how the test will be performed. The F1 key toggles the unit between single and combined. When in single test mode, only the measurement indicated by the F2 softkey will be made The F2 choices are C/N, CSO and CTB. The F3 key determines whether this will be an in-channel (manual) method or a gated measurement method. Manual measurements of CSO and CNR require removal of either the video modulation or the video carrier itself from the system temporarily while the measurement is being made. The manual measurement of CTB requires that the video carrier be removed from the system. CTB cannot be measured by removing only the video modulation because the CTB in most cable system falls directly on the video carrier frequency. We will look a little closer at this when we examine a typical results screen. While manual mode is an acceptable way of making these measurements, it is intrusive and requires either the ability to turn the carrier off remotely or the assistance of a second person to turn the carrier off manually. For these reasons, the gated measurement was developed. The gated measurement involves timing the CNR, CSO and CTB measurements to the incoming video signal. For CSO and CNR measurements it is possible to make gated measurements during a quiet line in the video signal without any external equipment on the headend modulator. CTB can also be measured during a quiet line of video, but requires a smart switch that will turn off the carrier itself during a chosen quiet line. A quiet line of video provides about 50 uSec of “no modulation” on the video carrier. For the AT2000Q, this is plenty of time to be able to make the CNR, CTB and CSO measurements. The AT2000RQ requires only 40 uSec per frame to make the measurements. The significance of this is that other analyzers on the market require 80 uSec per frame in order to be able to make an accurate measurement. Therefore, the same line in both fields must be used and in the case of CTB the carrier is turned off twice as many times per frame. On some television sets you will hear a slight popping noise when the carrier is being turned off for the 40 uSec interval. However, this faint popping noise becomes more objectionable to the customer as the frequency of it increases. Test equipment requiring 80 uSec per frame switching needs to have the carrier switched off twice as often and the resulting interference is higher in pitch and noticeably more objectionable. F4 asks whether or not you are using an external Bandpass filter on the unit while making this test. As discussed earlier, Bandpass filters are a good idea when making performance measurements with a spectrum analyzer because they prevent the front end of the analyzers from overloading. When F4 is set to YES, at AT2000RQ will be able to use less attenuation on the front end of the unit bringing it’s full dynamic range into play when making the C/N measurement. F5 will take the user to the measurement parameter setup screen. PRESS F5 NEXT SLIDE CCN Result Noise near Noise Correction Measurement Point March 2010 Proprietary & Confidential

44 Out-of-Band CCN Measurement
March 2010 Proprietary & Confidential

45 Instrument Noise Measurement
March 2010 Proprietary & Confidential

46 In Band CCN Measurement
NOTE: Noise measurement most be corrected for video bandwidth & instrument measurement errors. CNR In order to measure the noise within the bandwidth specified by the FCC, modulation must be removed making this an out of service measurement. It is accurate. Measurement Range March 2010 Proprietary & Confidential

47 Proprietary & Confidential
Gated CCN Measurement Another method for CNR measurements is the gated method. It measures noise on a quiet line of video (a signal to noise measurement) and then mathematically converts that to a CNR measurement. This measurement is accepted by the FCC,it is accurate, and is an in-service measurement. Perhaps the best thing about this measurement is that is what your customers see not what the system noise is. Quiet Line of Video March 2010 Proprietary & Confidential

48 Proprietary & Confidential
Setup CCN Measurement Center frequency = Video carrier frequency ==> SINGLE ==> COMBINED OR IN-CH ==> GATED Before actually initiating a test there are some procedures that need to be followed. It is highly recommended that a Bandpass filter be used when making performance measurements with any spectrum analyzer. The function keys on the right hand side of the AT2000RQ allow the user to determine how the test will be performed. The F1 key toggles the unit between single and combined. When in single test mode, only the measurement indicated by the F2 softkey will be made The F2 choices are C/N, CSO and CTB. The F3 key determines whether this will be an in-channel (manual) method or a gated measurement method. Manual measurements of CSO and CNR require removal of either the video modulation or the video carrier itself from the system temporarily while the measurement is being made. The manual measurement of CTB requires that the video carrier be removed from the system. CTB cannot be measured by removing only the video modulation because the CTB in most cable system falls directly on the video carrier frequency. We will look a little closer at this when we examine a typical results screen. While manual mode is an acceptable way of making these measurements, it is intrusive and requires either the ability to turn the carrier off remotely or the assistance of a second person to turn the carrier off manually. For these reasons, the gated measurement was developed. The gated measurement involves timing the CNR, CSO and CTB measurements to the incoming video signal. For CSO and CNR measurements it is possible to make gated measurements during a quiet line in the video signal without any external equipment on the headend modulator. CTB can also be measured during a quiet line of video, but requires a smart switch that will turn off the carrier itself during a chosen quiet line. A quiet line of video provides about 50 uSec of “no modulation” on the video carrier. For the AT2000Q, this is plenty of time to be able to make the CNR, CTB and CSO measurements. The AT2000RQ requires only 40 uSec per frame to make the measurements. The significance of this is that other analyzers on the market require 80 uSec per frame in order to be able to make an accurate measurement. Therefore, the same line in both fields must be used and in the case of CTB the carrier is turned off twice as many times per frame. On some television sets you will hear a slight popping noise when the carrier is being turned off for the 40 uSec interval. However, this faint popping noise becomes more objectionable to the customer as the frequency of it increases. Test equipment requiring 80 uSec per frame switching needs to have the carrier switched off twice as often and the resulting interference is higher in pitch and noticeably more objectionable. F4 asks whether or not you are using an external Bandpass filter on the unit while making this test. As discussed earlier, Bandpass filters are a good idea when making performance measurements with a spectrum analyzer because they prevent the front end of the analyzers from overloading. When F4 is set to YES, at AT2000RQ will be able to use less attenuation on the front end of the unit bringing it’s full dynamic range into play when making the C/N measurement. F5 will take the user to the measurement parameter setup screen. PRESS F5 NEXT SLIDE Noise Meas set 2 MHz Press F5 to setup Measurement parameters. March 2010 Proprietary & Confidential

49 Proprietary & Confidential
CCN Measurement CCN Result Noise near Noise Correction Measurement Point March 2010 Proprietary & Confidential

50 CATV Measurements Coherent Disturbances (CSO & CTB)
March 2010 Proprietary & Confidential

51 Second Order Inter-modulation
2IM = f1 ± f2 61.25 MHz MHz MHz CSO Any time 2 carriers are mixed together in a non-linear device such as a CATV amplifier, four output frequencies are produced. The sum, the difference, and the two originals. This produces interfering carriers in the video bandwidths of other channels. CSO is the result of several different carriers mixing together to produce a beat at the same frequency. This cumulative effect is know as Composite Second Order. MHz March 2010 Proprietary & Confidential

52 Third Order Inter-modulation
3IM = ± f1 ± f2 ± f3 61.25 MHz MHz MHz CTB MHz MHz March 2010 Proprietary & Confidential

53 Proprietary & Confidential
Where do the beats fall? Visual Carrier Composite Distortions are measured as a ratio in terms of dB down from the carrier. Lower Adjacent Aural Aural Carrier CTB CSO For Standard frequency allocation systems CTB fall on the picture carriers CSO fall ±1.25 MHz and ±0.75 MHz from the picture carrier 0.75 MHz .25 MHz March 2010 Proprietary & Confidential

54 Proprietary & Confidential
Digital Beat Products Add pix of digital channels beating together. March 2010 Proprietary & Confidential

55 Manual Measurement Procedures
Measure carrier peak Turn off carrier Set 30 kHz resolution bandwidth Narrow video bandwidth to 10 KHz Composite level using marker CSO or CTB = visual carrier - distortion level Automatic cable analyzers can makes CSO measurement without interrupting the subscriber March 2010 Proprietary & Confidential

56 Proprietary & Confidential
Setup CCN/CTB/CSO Center frequency = Video carrier frequency SINGLE ==> COMBINED IN-CH ==> GATED Before actually initiating a test there are some procedures that need to be followed. It is highly recommended that a Bandpass filter be used when making performance measurements with any spectrum analyzer. The function keys on the right hand side of the AT2000RQ allow the user to determine how the test will be performed. The F1 key toggles the unit between single and combined. When in single test mode, only the measurement indicated by the F2 softkey will be made The F2 choices are C/N, CSO and CTB. The F3 key determines whether this will be an in-channel (manual) method or a gated measurement method. Manual measurements of CSO and CNR require removal of either the video modulation or the video carrier itself from the system temporarily while the measurement is being made. The manual measurement of CTB requires that the video carrier be removed from the system. CTB cannot be measured by removing only the video modulation because the CTB in most cable system falls directly on the video carrier frequency. We will look a little closer at this when we examine a typical results screen. While manual mode is an acceptable way of making these measurements, it is intrusive and requires either the ability to turn the carrier off remotely or the assistance of a second person to turn the carrier off manually. For these reasons, the gated measurement was developed. The gated measurement involves timing the CNR, CSO and CTB measurements to the incoming video signal. For CSO and CNR measurements it is possible to make gated measurements during a quiet line in the video signal without any external equipment on the headend modulator. CTB can also be measured during a quiet line of video, but requires a smart switch that will turn off the carrier itself during a chosen quiet line. A quiet line of video provides about 50 uSec of “no modulation” on the video carrier. For the AT2000Q, this is plenty of time to be able to make the CNR, CTB and CSO measurements. The AT2000RQ requires only 40 uSec per frame to make the measurements. The significance of this is that other analyzers on the market require 80 uSec per frame in order to be able to make an accurate measurement. Therefore, the same line in both fields must be used and in the case of CTB the carrier is turned off twice as many times per frame. On some television sets you will hear a slight popping noise when the carrier is being turned off for the 40 uSec interval. However, this faint popping noise becomes more objectionable to the customer as the frequency of it increases. Test equipment requiring 80 uSec per frame switching needs to have the carrier switched off twice as often and the resulting interference is higher in pitch and noticeably more objectionable. F4 asks whether or not you are using an external Bandpass filter on the unit while making this test. As discussed earlier, Bandpass filters are a good idea when making performance measurements with a spectrum analyzer because they prevent the front end of the analyzers from overloading. When F4 is set to YES, at AT2000RQ will be able to use less attenuation on the front end of the unit bringing it’s full dynamic range into play when making the C/N measurement. F5 will take the user to the measurement parameter setup screen. PRESS F5 NEXT SLIDE Press F5 to setup Measurement parameters. March 2010 Proprietary & Confidential

57 Proprietary & Confidential
Initiate Measurement Set Frequency to Video Carrier Press F6 to MEASURE User is prompted to remove test carrier at the headend once test has been initiated Once all measurement parameters have been set, they need not be set again. With the analyzer set to the video frequency of the AT2000RQ, simply press the F6 MEASURE key. The user will be prompted too REMOVE TEST CARRIER AT HEADEND and PRESS ENTER TO CONTINUE. In a gated mode using a smart switch, the carrier will be turned off automatically. In manual mode, someone at the headend will need to turn off the carrier manually. For CSO and C/N measurements, only the modulation needs to be turned off. NEXT SLIDE March 2010 Proprietary & Confidential

58 Proprietary & Confidential
CCN/CSO/CTB Results CTB CSO CNR While some analyzers provide individual automated measurements of CNR, CSO and CTB, the AT2000 is the only analyzer that will perform all three simultaneously at the touch of a button. This is especially useful when gated measurements are made. This slide gives us a graphical representation of where the three measurements are made within the 6 MHz channel. As you recall the CNR and CSO measurement frequencies were adjustable in the parameters setup. Shown below is the saved result of a combined CN/CSO/CTB measurement with arrows added to show the graphical equivalent of the three measurements. The red trace is the trace which was plotted before the carrier was removed from the system and the black trace was made after the modulated carrier was turned off. Note the small hump in the black trace at the video frequency (center frequency). This small hump shows us the composite triple beat (CTB) in the system. Obviously, this measurement could not be made without removing the carrier because the carrier is on the exact same frequency as the video and would mask the CTB just as the video modulation would mask the CSO and CNR measurements if it was not removed. So in summary, the AT2000 will perform CNR as well as CTB/CSO distortion measurements both manually or gated. The gated measurements for CTB require some outboard switching equipment on the headend modulators, but are non-intrusive and can be done at any time of day or night. The ability to use only 40 uSec per frame makes the gated measurement even less likely to be detected by customers. The excellent dynamic range of the AT2000RQ provides the ability to make accurate measurements even in locations where signal levels are as low as 5 dBmv. These measurements are simple to perform and the results are easily stored and recalled for viewing or printing. March 2010 Proprietary & Confidential

59 CATV Measurements Low Frequency Disturbances or Hum
March 2010 Proprietary & Confidential

60 Proprietary & Confidential
Hum Definition Hum is ANY low frequency disturbance of the RF carrier Program modulation sometimes interferes with hum measurements causing the measurement to look worse than it actually is. Hum looks like AM modulation of the carrier HUM problems reduce MER and increase BER March 2010 Proprietary & Confidential

61 Proprietary & Confidential
How is Hum Measured? Demodulated Carrier Voltage Time Peak Peak-to-Peak % Hum = 100 X Hum is amplitude modulation of the visual carrier The level is a % of the total voltage FCC says 3% is limit March 2010 Proprietary & Confidential

62 Proprietary & Confidential
Hum Results March 2010 Proprietary & Confidential

63 Proprietary & Confidential
Digital HUM March 2010 Proprietary & Confidential

64 CATV Measurements In Channel Frequency Response
March 2010 Proprietary & Confidential

65 Response Specification
6 MHz Lower Channel Boundary Upper 1.25 MHz Visual Carrier 0.75 MHz 1 MHz 4.25 MHz Aural Carrier (Off or Suppressed)  2 dB Measurement Area March 2010 Proprietary & Confidential

66 Proprietary & Confidential
VITS Signals 525 LINES Horizontal Blanking SCAN MOTION Vertical Blanking Receiver Frame (Raster) 485 Vertical Sync March 2010 Proprietary & Confidential

67 Proprietary & Confidential
Multi-Burst To make this measurement the analyzer measures the amplitude of the different packets at different frequencies. The difference between the highest and lowest amplitudes can not be any more than 2 dB. March 2010 Proprietary & Confidential

68 Ghost Cancelation Reference
March 2010 Proprietary & Confidential

69 In-Channel Frequency Response Results Using GCR VITS
In Channel Response is an excellent test to perform to ensure that the channel under test has a flat response over the video spectrum. This test is generally performed on a line of video during the vertical blanking interval that has the appropriate test signal inserted at the Headend. The signal can be either a multiburst or a sweep. To multiburst signal must be a CATV multi-burst with packets of equal amplitude and equal duration. Some multiburst signals provide unequal amplitudes and durations and as a result will not give valid results. It is recommended that the correct multiburst signal be inserted on the channel at the headend whenever possible. This will ensure a valid test. March 2010 Proprietary & Confidential

70 Proprietary & Confidential
Digital Channels This was the stopping point from the 8/22/08 training session. Here is where we begin the next time. March 2010 Proprietary & Confidential

71 Proprietary & Confidential
Digital Measurements Levels Constellation MER, EVM BER Frequency Response Group Delay March 2010 Proprietary & Confidential

72 Proprietary & Confidential
Basic Components Consistent Wave Carrier (CW Carrier) Content MPEG stream Multiplexed video/audio streams HD video/audio Audio content Modem traffic VOIP traffic March 2010 Proprietary & Confidential

73 Proprietary & Confidential
CW Carrier Consistent Wave Carrier Sine wave shape At one consistent rate At one frequency Used to carry content over the network March 2010 Proprietary & Confidential

74 Proprietary & Confidential
CW Carrier Time Time Domain Frequency Domain March 2010 Proprietary & Confidential

75 Proprietary & Confidential
Multiple CW Carriers Frequency Domain F1 F2 Time Domain F1 F2 Time Time March 2010 Proprietary & Confidential

76 Proprietary & Confidential
Purpose of CW Carrier It’s the BUS Modulation is putting content on the Bus Demodulation is taking content off the Bus March 2010 Proprietary & Confidential

77 Proprietary & Confidential
Describing a sine wave Phase 90° Rate (Frequency): Time to complete a cycle Unit of measure = Hertz 1 cycle/sec = 1Hz Time Amplitude Ref. Point March 2010 Proprietary & Confidential

78 Putting Content on the BUS
AM ASK FM FSK Amplitude Modulation Frequency Modulation PSK Phase Modulation March 2010 Proprietary & Confidential

79 Proprietary & Confidential
Phase Relationships 90º 180º Time March 2010 Proprietary & Confidential

80 Bi-Phase Shift Keying (BPSK)
Simplest method of digital transmission. Data transmitted by reversing the phase of the carrier. Carrier amplitude & frequency remains constant. 1 bit transmitted at a time Advantage - Very robust method Disadvantage - Consumes significant bandwidth (1 bit per hertz) 180º The digital receiver is a phase discriminator that simply looks at the phase of the incoming signal. If the phase is at zero degrees, the receiver generates a 1; if the phase of the carrier is at 180º, then the receiver generates a 0. BPSK requires 1MHz of bandwidth to transmit 1 bit 1 March 2010 Proprietary & Confidential

81 Amplitude and Phase Modulation
Higher data rates are achieved by adding amplitude modulation to the carriers By having multiple levels of amplitude and phase more symbols can be transmitted in the same time period. 180º 00 01 10 11 Two Levels of Amplitude Modulation and Bi-Phase Modulation Makes Four Possible Symbols March 2010 Proprietary & Confidential

82 Proprietary & Confidential
QPSK Two carriers at the same frequency, 90º out-of-phase, transmitted at the same time One carrier is at 0º or at 180º, called the In Phase carrier – one carrier is at 90º or 270º, called the Quadrature carrier The resultant vector of these two carriers designates the symbol to be transmitted. A symbol is a digital word that is a combination of several bits. In this case the symbol contains two bits Using this method twice as much data can be transmitted in the same amount of bandwidth. March 2010 Proprietary & Confidential

83 How QPSK symbols are transmitted
10|11|01|00|11 10 11 01 00 11 The digital receiver analyzes both the phase and the amplitude of the incoming signal and produces a bit stream that corresponds to that signal. March 2010 Proprietary & Confidential

84 Symbols, Symbol Rate, Bit Rate
The Digital Language If bits are the letters, then symbols are the words in the language of digital modulation. The bit rate is the number of bits sent per second Symbols transmit one or more bits of digital information. Symbol Rate is the number of symbols sent per second. The transmission bandwidth is the symbol rate. Symbol Rate = Bit Rate / Number of bits per Symbol The Symbol rate is = bit rate/ the number of bits transmitted with each symbol. This is also referred to as baud rate. If a QPSK modulation scheme can transmit 2 bits for each symbol, then the symbol rate for the 100Mbps bit rate would be 50MHz. H March 2010 Proprietary & Confidential

85 Proprietary & Confidential
Describing a sine wave Phase 90° Rate (Frequency): Time to complete a cycle Unit of measure = Hertz 1 cycle/sec = 1Hz Time Amplitude Ref. Point March 2010 Proprietary & Confidential

86 Proprietary & Confidential
QPSK Example: I carrier transmitted at 0º, Q carrier transmitted at 90º. Resultant vector at 45º represents a symbol of 11. If we needed to transmit a 01, then the I carrier would be at 0º and the Q carrier would be at 270º. 90º 10 135º 11 45º 180º I Carrier 00 225º 01 315º 270º Q Carrier March 2010 Proprietary & Confidential

87 Quadrature Amplitude Modulation (QAM)
Analog color subcarrier similar to QAM modulation Two signals carried at the same frequency out of phase Two carriers called the I and Q, each carrying one-half of the data. Each I & Q carrier transmits 8 levels of data for 64 QAM Hence 82 equals 64 combinations or 64 QAM March 2010 Proprietary & Confidential

88 In-Phase and Quadrature
180 Deg Shift I Channel t Carrier Phase I + = Carrier Q Amplitude Q Channel Carrier t Carrier Phase Shift over time Phase 90° Shifted March 2010 Proprietary & Confidential

89 Proprietary & Confidential
Creating a QAM signal I & Q carriers, same frequency, but phase shifted by 90° AM modulated Combined make up the QAM signal. Local Osc 8 Level AM Modulator Bit Stream Oscillator Shifted 90° Combiner 64 QAM Signal Q Component I Component March 2010 Proprietary & Confidential

90 Proprietary & Confidential
QAM QAM is Quadrature Amplitude Modulation Two carriers at the same frequency, 90º out-of-phase, transmitted at the same time Uses multiple levels of amplitude & phase modulation Each carrier is a representation of half of the transmitted symbol. March 2010 Proprietary & Confidential

91 Proprietary & Confidential
QAM (Cont.) If each of the I and Q channels transmits 4 levels of data 16 symbols transmitted in one clock cycle Each symbol contains 4 bits Known as 16QAM 8 levels per carrier 64 symbols transmitted Symbol contains 6 bits 64QAM 16 levels per carrier 256 symbols transmitted Symbol contains 8 bits Known as 256QAM March 2010 Proprietary & Confidential

92 Proprietary & Confidential
Vectors and 16 QAM Q 90° 11 1011 1011 1111 10 1010 1110 I 180° I 0° 00 01 10 11 01 This slide looks at a 16 QAM carrier. That means that each symbol is 4 bits (2 to the 4th = 16) In this slide if we wanted to transmit the bit stream 1010, we would modulate the I carrier with .35 volts and the Q carrier with .35 volts. This produces a resultant vector where that symbol is mapped in the constellation. The symbols are mapped so that if an error occurs in the vector, the resultant 4 bit word will only off by one bit. We are also transmitting the digital bit stream using analog transmission techniques. At the receive end the 2 carriers are demodulated and vectored to produce the original bit stream. 0001 0101 00 0000 0100 Q 270° March 2010 Proprietary & Confidential

93 Proprietary & Confidential
Vectors and 16 QAM Q 90° 11 1011 1011 1111 10 1010 1110 I 180° I 0° 00 01 10 11 01 In this example ingress from the coaxial plant has changed the levels of the I and Q carriers before they arrive at the digital receiver. As a result of this the new vector is not on the target anymore. There is then also a vector difference, shown in blue, between the target and the where the symbol actually falls. The difference between the target and the new resultant vector is MER or Modulation Error Ratio. The higher the MER, the closer the symbols fall to the target vector. The lower the MER, the farther away they fall. If they fall far enough away, then they cross the decision boundary, shown in the blue dotted line, and the receiver generates the wrong symbol causing a bit error. 0001 0101 00 0000 0100 Q 270° March 2010 Proprietary & Confidential

94 Proprietary & Confidential
64 QAM Constellation . With 64 QAM, 6 bits are transmitted at a time requiring 8 different states on each carrier to represent 3 bits each on the in phase and the quadrature carrier. Each axis contains 8 different states 6 Bits per Symbol March 2010 Proprietary & Confidential

95 Proprietary & Confidential
256 QAM 256 QAM transmits 8 bits at a time or 8 bit symbols. Each axis requires 16 different states 8 Bits per Symbol March 2010 Proprietary & Confidential

96 Proprietary & Confidential
Digital Measurements Digital Channel Power MER, ENM, and EVM Constellation Impairments Pre and Post FEC BER Adaptive Equalizer QIA Measurements March 2010 Proprietary & Confidential

97 Analog vs. Digital Power Measurements
300 KHz 6 MHZ 6 MHZ Both signals are 6 Mhz wide, however the digital signal contains more power within the same 6 MHZ. Analog signals are measured using peak power measurements over a very narrow bandwidth. Digital signals are measured over a relatively wide band width using average power measurements. March 2010 Proprietary & Confidential

98 Proprietary & Confidential
Digital Power Measurement H March 2010 Proprietary & Confidential

99 Balancing System Levels
Because more power is contained in the 6 MHz digital signal, the power must be derated so that amplifiers in the CATV system are not overdriven. Digital carriers are normally 6-10 db below video carriers (avg. power to peak power) Due to the fact that the detector operates in different modes for the two different measurements, they cannot accurately be displayed on the analyzer at the same time. March 2010 Proprietary & Confidential

100 Modulation Error Ratio
MER is used as a single figure of merit for quality for RF digital carriers It includes distortions such as CCN, CSO, CTB, laser compression, etc…. The sum of all evils. A 256 QAM picture tiles at 28dB MER A minimally good MER is 31 dB for 256 QAM at the back of the customer’s set. H March 2010 Proprietary & Confidential

101 Proprietary & Confidential
Vectors and 16 QAM Q 90° 11 1011 1011 1111 10 1010 1110 I 180° I 0° 00 01 10 11 01 In this example ingress from the coaxial plant has changed the levels of the I and Q carriers before they arrive at the digital receiver. As a result of this the new vector is not on the target anymore. There is then also a vector difference, shown in blue, between the target and the where the symbol actually falls. The difference between the target and the new resultant vector is MER or Modulation Error Ratio. 0001 0101 00 0000 0100 Q 270° March 2010 Proprietary & Confidential

102 Proprietary & Confidential
MER and a Constellation H March 2010 Proprietary & Confidential

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MER and a Constellation H March 2010 Proprietary & Confidential

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Acceptable MER 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. March 2010 Proprietary & Confidential

105 Constellation Analysis
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106 Proprietary & Confidential
Noise Impairments This is an accident waiting to happen. The impairment on this 64QAM signal is a pure noise impairment that is on the verge of failing. The pictures will be perfect, but the signal is only a dB away from failing at an MER of A one or two dB drop in system levels will cause these pictures too tile. March 2010 Proprietary & Confidential

107 Proprietary & Confidential
Phase Impairments Looks good here in the Headend! March 2010 Proprietary & Confidential

108 Coherent Interference Constellation
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109 Coherent Interference in Freq Spectrum
Ingress from UHF off-air channels Headend beats CSO & CTB March 2010 Proprietary & Confidential

110 Proprietary & Confidential
Phase Impairments This is an example of a constellation with a phase impairment. Phase impairments are most often generated in the headend modulators and/or upconverters. Notice the entire constellation appears to be rotating about the center of the constellation. March 2010 Proprietary & Confidential

111 Proprietary & Confidential
Gain Compression Gain Compression can be caused by IF and RF amplifiers and filters. The symbols on the outside of the constellation seem to be pulled in toward the center. H March 2010 Proprietary & Confidential

112 Proprietary & Confidential
I/Q Gain Imbalance I/Q imbalance when the display is taller than it is wide. This is an indication that the modulator is not amplifying the I and Q carriers equally. H March 2010 Proprietary & Confidential

113 Proprietary & Confidential
Laser Compression March 2010 Proprietary & Confidential

114 Proprietary & Confidential
CM2000/2800 Constellation March 2010 Proprietary & Confidential

115 Proprietary & Confidential
BER Measurement March 2010 Proprietary & Confidential

116 Proprietary & Confidential
What is BER? BER is defined as the ratio of the number of wrong bits over the number of total bits. Sent Bits Received Bits Every QAM signal on the cable system employs some type of Forward Error Correction. There is an entire seminar on our website concerning FEC and BER if you would like more information on the subject. The FEC (forward error correction) is extra data transmitted simultaneously with the programming data on the QAM signal. The FEC data contains information that is used in the receiver todetermine if each bit of data being received is correct. FEC data is added into the data stream at regular intervals as the data is being encoded for transmission. When the signal is received at the far end by a set top box or a cable modem, the unit can determine whether errors have occurred or not. If an error has occurred, the FEC circuitry corrects the error if it can. The FEC can correct a certain number of errors, but if the signal is badly degraded it will not be able to correct all of them. The BER or Bit Error Rate is simply the ratio of the number of erred bits divided by the total number of bits received. error # of Wrong Bits 1 0.1 BER = = = # of Total Bits 10 March 2010 Proprietary & Confidential

117 Proprietary & Confidential
BER Display BER is normally displayed in Scientific Notation. The more negative the exponent, the better the BER. Better than 1.0E-6 is needed after the FEC for the system to operate. Lower and Better BER One error out of ten would be a ratio of 1/10 or 0.1 or written in Scientific notation 1E-01. One error out of a thousand bits would be 1/ or or E-03 One error out of a billion would be 1/1,000,000,000 or or 1E-9 Two errors out of a billion would be 2/2,000,000,000 or or 2E-9 When it comes to scientific notation and BER, the more errors there are over a given time period, the bigger the number to the right of the E becomes. This is the most significant number in the scientific notation. The large the number to the right of the E, the better the performance. The lower the number to the right of the E, the worse the performance. The number to the right of the E is pretty much insignificant. It is like buying a lottery ticket. What is the difference that your chances are one in a billion or two in a billion. The same with BER. There is little difference between one error in a billion bits or two errors in a billion bits. March 2010 Proprietary & Confidential

118 Calculated Bit Error Rate
Using the amount of FEC overhead required to reproduce a bit string, the bit error rate can be calculated. Using the FEC to determine the BER allows BER to be measured without removing the service which is usually required for most BER testing. March 2010 Proprietary & Confidential

119 Forward Error Correction Decoder
Forward error correction (FEC) is a digital transmission system that sends redundant information along with the payload, so that the receiver can repair damaged data and eliminate the need to retransmit. Reed Solomon can correct bit errors down to approximately 1 bit for every 1000 (10-6). If you have bit errors at 10-6, you need to start looking for your problems. March 2010 Proprietary & Confidential

120 Proprietary & Confidential
Pre and Post FEC errors Pre FEC errors Errors that have occurred before the FEC has had an opportunity to correct any of the errors. Post FEC errors Errors that could not be corrected A cable modem will tolerate pre-FEC errors and the FEC will continue to correct pre-FEC errors up until 1E-06 or one error in one million bits. After that the FEC can do no more. Post-FEC errors will cause retransmissions requests and slowdowns in a DOCSIS systems. The main point of this slide is that while pre-FEC errors can be tolerated in a DOCSIS systems, you want to avoid post-FEC errors because they can cause retransmissions and make the network slower than it really is. Again, more detailed training is available on website at March 2010 Proprietary & Confidential

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Pre and Post FEC BER To get an accurate idea of the BER performance you need to know both the pre and post FEC bit error rate. The FEC decoder needs a BER of better than 1 E-6 in order to operate. Post FEC Bit errors are not acceptable. You should look at both the Pre and Post FEC BER to determine if the FEC is working to correct errors and if so how hard. Pre FEC BER FEC Decoder Post FEC BER March 2010 Proprietary & Confidential

122 Proprietary & Confidential
Parity By adding an additional bit to a group of bits, errors can be detected within the group. This is known as a parity bit. Even parity means that when the parity bit is added the group of bits including the parity always has an even number of ones. Odd parity means the group would have an odd number of ones. If after transmission the number of ones is no longer even (for even parity), then there must be an error. Error Odd Number of Ones Indicates Error Always Even Number of Ones (Even Parity) Parity Bit March 2010 Proprietary & Confidential

123 How Reed Solomon FEC Works
FEC works by addition additional data bits to the data stream to determine if errors exist and to try and correct them. 1011 1 1000 1 0100 1 1100 0 Video Data Stream 1=odd 0=Even FEC sort of works like a financial spreadsheet. All the columns and rows must add up and then the totals of all the columns and rows must add correctly as well. If they don’t then there’s an error and the data must be fetched from the transmitted redundant data. Stream With FEC Added March 2010 Proprietary & Confidential

124 Proprietary & Confidential
How Reed Solomon Works Once you know a bit is wrong, correcting it is easy, if you know its wrong and its a zero, then it has to be a one. 1011 1 1000 1 0100 1 1100 0 1011 1 1000 1 1001 1 0100 1 1100 0 1=odd 0=Even Error Before Transmission After Transmission the Bit in Error is Detected and Corrected March 2010 Proprietary & Confidential

125 Proprietary & Confidential
BER and a Constellation H March 2010 Proprietary & Confidential

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CM2000/2800 Constellation March 2010 Proprietary & Confidential

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Statistical Mode The Statistics mode shows MER, and Pre and Post BER over a period of time. The measurements are made once per second and the average of all the meausrments made over the time period is displayed. This mode would capture problems that would not show up in instantaneous measurements. March 2010 Proprietary & Confidential

128 Proprietary & Confidential
Statistical Mode The Statistics mode shows MER, and Pre and Post BER over a period of time. The measurements are made once per second and the average of all the meausrments made over the time period is displayed. This mode would capture problems that would not show up in instantaneous measurements. March 2010 Proprietary & Confidential

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Adaptive Equalizer Every Digital Receiver has an Adaptive Equalizer It performs 3 functions Compensates for amplitude imperfections of the digital signal Compensates for group delay Rings at the symbol rate to only allow one symbol at a time into the digital receiver March 2010 Proprietary & Confidential

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Equalizer Mode March 2010 Proprietary & Confidential

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Equalizer Mode March 2010 Proprietary & Confidential

132 Digital Video – EQ Control
Standard EQ Used in current equipment More taps Improved correction Min EQ Less taps Mirrors performance of old equipment Disables Auto Diagnosis March 2010 Proprietary & Confidential

133 Proprietary & Confidential
Frequency Response Effective span equal to symbol rate Measurement calculated using Equalizer data March 2010 Proprietary & Confidential

134 Proprietary & Confidential
Amplitude Ripple A spectrum analyzer may be used to characterize a downstream digitally modulated carrier’s in-channel frequency response, essentially using the noise-like signal to measure itself. This method eliminates the need to take the digitally modulated carrier out of service, and does not require a sweep signal. An in-service spectrum analyzer measurement March 2010 Proprietary & Confidential

135 Proprietary & Confidential
Group Delay Definition: Group delay is a measure of how long it takes a signal to traverse a network, or its transit time. It is a strong function of the length of the network, and usually a weak function of frequency. It is expressed in units of time, pico-seconds for short distances or nanoseconds for longer distances. Measured in units of time, Typically nanoseconds (ns) over frequency Or, Delay per MHz. In simplified terms, when there is no group delay in a system, network or component, all frequencies within a defined bandwidth will take the same amount of time to traverse that system, network or component. When group delay does exist, signals at some frequencies will arrive at slightly different times than signals at other frequencies will. Group delay in a CATV network is usually related to frequency response problems, and is most often a problem near band edges and diplex filter rolloff regions. March 2010 Proprietary & Confidential

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Group Delay (Cont.) In an ideal system all frequencies are transmitted through the system, network or component with equal time delay Frequency response problems cause group delay problems Group delay is worse near band edges and diplex filter roll-off areas March 2010 Proprietary & Confidential

137 Proprietary & Confidential
Group Delay (cont’d) Excessive group delay increases bit error rate due to inter-symbol interference DOCSIS spec. no greater than 200nSecs per MHZ Spec should be less than 100 nSecs per MHz Data equipment manufacturers may have various group delay requirements for their products, depending on data rate, modulation type, etc. For example, one manufacturer may state that as long as upstream path group delay remains below 80 nanoseconds in the data signal’s passband from the subscriber to the headend, then the device will meet published bit error rate (BER) performance as it relates to group delay. The DOCSIS specification for upstream group delay is 200 nanoseconds/MHz. As long as frequency response is maintained as flat as possible, and digitally modulated carriers are kept away from band edges or diplex filter rolloff areas, then group delay should not be a problem. The best way for a cable operator to maintain flat frequency response to to sweep the network on a regular basis. March 2010 Proprietary & Confidential

138 Group Delay Measurement
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QIA Screen March 2010 Proprietary & Confidential

140 QAM Impairment Analysis (QIA)
I/Q Gain and Phase The phase and gain of both the I and Q carrier must be equal in order for the constellation to be correct. This impairment is caused by the QAM modulators. The gain difference between the 2 carriers should be less than 1.8% and the phase difference should be less than 1 degree. Echo Margin A measurement in dB of how far the taps are from the template with the time equalizer measurement. Caused by impedance mismatches in the system. Should be at least 6 dB. March 2010 Proprietary & Confidential

141 Proprietary & Confidential
QIA Continued Carrier Offset Carrier frequency test. Should be no more than +/- 25KHz Estimated Noise Margin Difference in dB between MER and the digital cliff Depends on if the signal is 64 or 256 QAM Minimum depends on where the measurement is taken Example if the Minimum MER for 256 QAM is 28 and the measurement is 34, than the ENM is 6 Frequency Response Frequency response of the digital carrier Should be less than 3 dB pk-to-pk March 2010 Proprietary & Confidential

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QIA Continued Hum Low frequency disturbances of the digital carrier Same as hum on analog carriers, if the level is the same, it’s the system, if higher on the digitals then it’s probably the QAM modulator Symbol Rate Error Should be less than +/- 5 ppm Phase Noise Jitter (changes in phase) of the oscillators, most likely the up-converter The phase shift or jitter should be less than .5 degrees March 2010 Proprietary & Confidential

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QIA Continued Group Delay Different frequencies travel through the same medium at different speeds. So the lower the lower frequencies of the same carrier arrive at the receiver at different timing than the higher frequencies. Should be less than 50 nSec pk-to-pk Compression Caused by overdriving lasers or amplifiers Shows up as corners pulling in at the outer corners of the constellation Should less than 1% March 2010 Proprietary & Confidential

144 Proprietary & Confidential
System Sweep March 2010 Proprietary & Confidential

145 What does sweep do for the technician?
Measures the Frequency Response of the network Confirms Unity Gain View impedance mismatches Bad connectors & cable Bad devices Checks both Forward and Return paths Concept: If the system is flat and levels are correct, distortion will be minimal March 2010 Proprietary & Confidential

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Why Sweep? Insures proper headroom Preventative Maintenance Non-obtrusive measurement Look at network with a microscope March 2010 Proprietary & Confidential

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CM2800 Sweep Compatible with 3010H/R Forward Sweep New 3 Dwell definition Simultaneous Pilot & Forward Sweep Results Return Sweep Switch Control (Phase 2) Return Spectrum (Phase 2) March 2010 Proprietary & Confidential

148 Proprietary & Confidential
Sweep System Facts CM2800 compatible with 3010 version 5.53 firmware only 3010R & 3010H, same measurement hardware 3010H ships fully loaded Basic unit support Return Path Monitor mode (both R&H) Option 052 – Forward Sweep TX & Dual Path Mode Option 061 – Switch control 3010 upgrade to ver. 5.53 Version 4.x & above included with Calibration Version 3.x available for an additional charge March 2010 Proprietary & Confidential

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Sweep Application Forward & Reverse Sweep March 2010 Proprietary & Confidential

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Forward Sweep Forward Sweep Path 3010 Output Combined with Downstream Signals Sweep Level 16dB to 20dB below analog levels Sweep tilt = channel tilt Normalized sweep is a relative meas. Change in response between meas. Point and reference point March 2010 Proprietary & Confidential

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Reverse Sweep Reverse Sweep Path DS Comms Combined with Downstream Signals (Comms only) Test signal inserted in field, measured by 3010H, meas. sent to field instrument on DS Comms Must know your reference points & design levels March 2010 Proprietary & Confidential

152 Proprietary & Confidential
Network basics Unity Gain Concept Total System Gain equals Total Loss Gain = Loss or Gain/Loss = 1 Forward Path: Constant Output Levels Amp compensates for cable before device Return Path: Constant Input Levels Amp compensates for cable after device Same cable forward amp is compensating for. Sweep Insertion ~ 17 dB Below Channels System Level to Sweep Delta will Remain Consistent Matches Design Level Tilt March 2010 Proprietary & Confidential

153 Reality of Frequency Response
Output Levels and Slopes are customized to provide the best performance Highest Carrier to noise Ratio (CC/N & MER) Highest Carrier to Distortion Ratio (CSO, CTB, ect.) March 2010 Proprietary & Confidential

154 How Sweep Works with no Sweep Table
50 450 1 MHz 400 measurement points Transmitter output with a blank sweep table. Sweep Resolution = (Stop freq... - Start freq...) 400 points = (450MHz - 50MHz) 1MHz/point Before we cover the setup procedure, it is important to understand how the sweep signal is generated. If you created a blank sweep table in the transmitter with a start frequency of 50MHz and a stop frequency of 450MHz, the transmitter would product 400, 5usec sweep points 1MHz apart as shown above. The sweep frequency resolution is determined by the start and stop frequencies in areas of the spectrum where no frequencies are in the sweep table. March 2010 Proprietary & Confidential

155 Components of the Sweep Table
Stop freq... = 450MHz Start freq... = 50MHz 57.20MHz 63.20MHz 61.25MHz The Sweep table is used to protect areas of the spectrum from sweep energy and to define carriers for the receiver to measure as part of the sweep response. Above the red lines represent the sweep measurement points, the dashed green lines represent the sweep measurement points that are guarded by the guard band and therefore not measured, and the solid black line indicates the raw sweep response. The block and frequency indicator at 61.25MHz, the visual carrier of channel 3, is present in the table with a 1 dwell. The 1 dwell will cause the receiver to measure the carrier for 100usec. The level of the carrier will be displayed in raw sweep and over the F3 softkey. The sweep table above is an example of a Phantom carrier table. The Phantom carrier locations are indicated above and are used as place holders for the guard bands. In Phantom Scan, the user defines where sweep should not take place and the transmitter fills in the blank spots in the spectrum. The screen resolution of the 3010 is 222 points. The 400 measurement points of sweep data is compressed to 222 points in order to display the data on the screen. If you change the viewed span to half the span set in the transmitter, you can view the transmitter resolution within that area of the spectrum. This can be used to troubleshoot problems in the system or checking variations in the sweep when creating or editing a sweep table. March 2010 Proprietary & Confidential

156 What is the Forward Path of the Cable System
Return Equip. R H L Forward Signal Path Signal flow in the forward path is from the headend to the customers home as indicated by the blue arrows. Each amplifier compensates for the loss in the wire before the amplifier under test. In the forward path, signals originate at the headend and are transmitted to many customer drops. One output feeds many inputs. In the forward system the outputs of like devices are typically set to same output level. Each amplifier compensates for the cable and passive loss before it. This principal (Gain = Loss) is Unity Gain. Level changes in the forward path occur due to changes in cable loss caused by temperature. Automatic level or gain controls (ALC or AGC) are located in the amplifiers. A section of the alignment procedure for the forward path involves setting the operating point for the automatic control circuit. This procedure include measuring the absolute level of the pilot channels used in the system and comparing the levels to the calculated levels for the current temperature. If the pilot frequencies are entered into the sweep table as measured frequencies, the automatic control system can be adjusted in the normalized sweep mode eliminating the need to change measurement modes. March 2010 Proprietary & Confidential

157 Lash-Up for Forward Sweep Set Up
To Forward Lasers RF In RF Out Forward Combiner This slide shows the lash-up of the 3010H and 3010R required to setup the forward sweep table. As shown, the output of the headend combiner should be connected to the input of the 3010H. This connection is only needed scanning the signals on the system in order to create the basic sweep table. You do not need this connection after the system is setup or if you are editing an existing sweep table. In most cases, the sweep table is created in the 3010H and transferred to the 3010R’s in the system via the Forward pilot. The 3010R connected as shown above is only used to set the output level and slope of the 3010H. Normally the sweep is set 10 to 15dB below the visual carriers on the system in order to minimize interference to the channels on the system. March 2010 Proprietary & Confidential

158 Forward Sweep Setup Flow
Setup Channel plan Connect the input of the 3010 to a port containing all the channels on the network Set Forward Sweep mode to Fast In the Sweep Parameters screen set the following: Start Freq. to your start frequency Stop Freq. to your stop frequency Comm’s Pilot Freq. to a clear area of network spectrum Scan Type to Phantom Channel Plan to the Channel Plan you created Sweep Table to None March 2010 Proprietary & Confidential

159 Forward Sweep Parameters Screen
3010H Start Frequency Scan Type Frequency Plan Created for system under test Stop Frequency The Current Sweep Parameters screen is used to start and the stop frequency the transmitter will use to limit the sweep bandwidth. Most systems will set the start frequency 10 to 20 MHz below and the stop frequency 10 to 20 MHz above the actual frequency of concern. This allows the technician to view any system roll-off at the band edge of the system. It also ensures that no guard bands fall outside the start and stop frequencies. The Pilot frequency is the communications frequency between the transmitter and the receiver. It can be set to any frequency between 5 and 1000MHz. It must be set within the forward bandwidth. There are two different scan types, Standard and Phantom. Scan Type refers to the method used to create a new sweep table when scanning the system for signals. Standard scan will create a sweep table made up of the visual and aural frequencies with 1 dwell times and a guard band of 2.2MHz in an NTSC system. Phantom scan will create a sweep table with the frequencies equal to the visual frequency plus 1.95 MHz, with a guard band of 2.9 MHz and a dwell time of 0. The channel plan should be set to the frequency plan created for your system. It is used to scan the system when creating a new sweep table. To create a new sweep table the ‘Swp Table’ item should be set to None. Connect the input of the 3010H to a system test point and press F3 to continue. Communications Pilot Frequency Sweep Table (Set to None to create a new table.) March 2010 Proprietary & Confidential

160 Forward Sweep Setup Flow
Scan the network and the instrument creates the basic Sweep table for you Add system pilots and edit table Save the table Set the level & slope Your done!!!! March 2010 Proprietary & Confidential

161 Table Entries for other type signals
Digital Signal (Places sweep point between Digital Channels) Frequency = Channel Center Freq.. Guard band = 1/2 Channel bandwidth Dwell = 0 (Measures Digital channel, no sweep point) Frequency = Channel Center Freq. Guard band = ½ Channel bandwidth MHz Dwell = 3 Phantom Carrier Setup (Sweep point in Vestiges Sideband) Frequency = Center Freq kHz Guard band = ½ Channel bandwidth – 0.1 MHz System AGC or Setup Pilot Channels Frequency = Video carrier frequency Guard band = 1MHz There are many types of carriers on the network. These are some of the common ones. If you are not sure of the type or frequency of a signal, you can use the spectrum scan mode to measure it. Set the start and the stop frequencies so the signal and the edges can be seen. Use the marker to measure the start frequency of the signal. Write down the value. Now move the marker to the stop frequency of the signal. Write down the value. Subtract the start frequency from the stop frequency to find the span of the signal. Divide the difference in half. Add this number to the start frequency and round it to two decimal places to calculate the center frequency of the signal. This is the frequency you will enter into the sweep table. Now take the number and round it to one decimal place to calculate the guard band. In most cases you will probably use a 0 dwell for these type signals. March 2010 Proprietary & Confidential

162 Proprietary & Confidential
Forward Sweep Level Sweep points between Digital Channels Sweep points must be at least 17dB or greater below analog video level No sweep points around Digital Channels Sweep points should be at the same level as the measured digital channels March 2010 Proprietary & Confidential

163 Proprietary & Confidential
Sweep Setup Go to SETUP / SWEEP Enter / Select the Low and High System Pilot Enter the Forward Sweep Communications Pilot Frequency (per 3010 setting) Enter the Reverse Sweep Communications Pilot Frequency (per 3010 setting) Check “Get New Table” to force download of new Forward Sweep SAVE & EXIT March 2010 Proprietary & Confidential

164 Proprietary & Confidential
Sweep Setup Go to SETUP/LIMITS and SWEEP tab Select the Location from the Pull Down Menu Set the Downstream Sweep Limits for Low System Pilot min & max High System Pilot min & max Tilt max (we will add min) Peak-to-valley max Set the Upstream Sweep Limits for Tilt max (we are adding min) SAVE & EXIT Sweep Limits Screen March 2010 Proprietary & Confidential

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Sweep Tools View Sweep Table March 2010 Proprietary & Confidential

166 Screen Annotations – Forward Sweep
Save Ref. File Freq. & dB/Div Control View Sweep Table Trace control (only active when reference is selected) Site File Select Reference Attenuator Sets Dynamic range P/V freq. range set by Vert. Marker Position System Pilot Freq. & Level March 2010 Proprietary & Confidential

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Forward Sweep Lock Symbol First Connection Communication Icon (lock symbol) will flash yellow, Markers & start stop will update. If Comms Icon not flashing - Adjust Attenuation If test point system levels are > 10 dBmV, increase the attenuator setting. If < 0 dBmV, decrease attenuator setting. Wait for sweep table download (or press F4 on 3010) Note the sweep trace and the pilot graphs. Pilots should be 10 to 15 dB above sweep. Note markers Use Touch Screen or Arrows Tilt & Peak-to-valley Calculated on Markers Click on the SAVE icon at top tool bar and enter a name for a reference file. March 2010 Proprietary & Confidential

168 Proprietary & Confidential
Sweep Reference Sweep File are used as a Reference Select a Reference File Sweep Display will be the difference between Ref and current results March 2010 Proprietary & Confidential 168

169 Referenced Forward Sweep
Click REFERENCE, select saved file. RED trace = Live Trace – Reference Trace Automatically adjusts to 2 dB/Div Click A, B, A&B, A-B to toggle Trace (Live, Reference, Both or Difference Traces) Low & High Pilot Frequency & Levels are Displayed Tilt & Peak to Valley calculations based on Vertical Marker Position March 2010 Proprietary & Confidential

170 Return Sweep Configuration
Return Signal Path H L R R Return Equip. Each amplifier compensates for the loss in the wire after the amplifier under test. In the return path, signals originate at the customer drops and are transmitted back to the headend. Many outputs feeding one input. Each amplifier compensates for the cable and passive loss after the return amplifier. This is the same physical cable the forward amplifier is compensating for at a given location. In the return path, devices are adjusted for a consistent input level at the next device. This make testing more difficult because the measurement or common reference point is some distance from adjustment point. To accomplish the task the technician needs a method of making a measurement at one location and viewing measurements from a different location. The 3010H/R performs this function. Level changes in the return path are also effected by temperature as in the forward path, however the largest contributor to return level changes is the placement of the equipment and differences in the passive loss between the equipment and the amplifier. In order to control the output level of devices installed in the system, the data receiver installed at the headend monitors the receive levels from each device and adjusts the levels automatically. The balancing of the return path is critical for this system to operate correctly. Signal flow in the return path is from the customers home to the headend as shown by the blue arrows. March 2010 Proprietary & Confidential

171 Alignment Issues & the Return Path
The monitor point is some distance from the adjustment point. The communications between the 3010R and 3010H is through the system under test. Interference on the return or forward path can affect the communication between the instruments. The Ingress detection system is used to troubleshoot interference on the return path. As you can see from the slide above, there are some issues that must be considered when sweeping the return path. It is important to remember the measurements are being made at the 3010H in the headend and you are inserting a signal at the test point in the field. In other words, the 3010R is used as a display device to show what is happening at the 3010H. This will help keep things in perspective as you locate problems in the system and setup the 3010’s to make these measurements. March 2010 Proprietary & Confidential

172 Reverse Sweep Communications
Reverse Sweep Path DS Comms Combined with Downstream Signals (Comms only) Test signal inserted in field, measured by 3010H, meas. sent to field instrument on DS Comms Must know your reference points & design levels March 2010 Proprietary & Confidential

173 Proprietary & Confidential
3010H Polling Sequence Here is the Polling Sequence for the 3010H. First, the 3010H will service any instruments already on line. It remembers the polling ports for each unit and will set the switches accordingly. Next the 3010H sends a New User Poll message on the Forward Pilot. It then sets the switch string to the next polling set in the sequence, and begins to monitor the return pilot frequency for field units. If it does not receive any signal it repeats the last steps. If the 3010H receives data at the Return Pilot frequency and it is good data, it logs the field unit on the system and services the unit. If the data is bad, the 3010H assumes it is ingress, makes a Spectrum Scan measurement, and broadcasts the measurement data on the Forward Pilot. This is call the ‘Broadcast Ingress Message’ in the instrument manual. The 3010H then repeats the sequence. March 2010 Proprietary & Confidential

174 Return Sweep Headend Lash-Up
Forward Combiner To Forward Lasers RF out Return Receivers In order to begin setting up the return sweep, the system requires communication in both the forward and reverse direction. This can be accomplished by wiring the headend as shown or by connecting the 2 units back to back. RF in To Return Processing Equipment March 2010 Proprietary & Confidential

175 Connecting the 3010R to the 3010H back to back
Output Output Input 3010H Input This slide shows how to connect the units back to back for system testing. Sometimes this is necessary to confirm the operation of the units. March 2010 Proprietary & Confidential

176 Proprietary & Confidential
Return Sweep Setup Set dynamic range for measurement Full Scale (FS) setting in Spectrum Scan If < 5 return paths connected to 3010 or using AT1600 Switch Set FS for modem traffic to upper division of display If > 5 return paths Set FS for noise floor below second division of display Remember the setting! March 2010 Proprietary & Confidential

177 Return Sweep Setup (Cont.)
Set Switch driver if connected to a switch Set Return Sweep mode to Fast In Return Sweep Parameters screen set the following: Start Freq. to your start frequency Stop Freq. to your stop frequency Forward Pilot to a clear area Forward Path spectrum Return Pilot to a clear area Return Path spectrum Ret Swp Table to None (to create new table) March 2010 Proprietary & Confidential

178 Return Sweep Setup (Cont.)
To Speed up sweep Enter frequency every 1 MHz Guard band = 0.5 MHz Dwell = 0 Save Table Set Forward Pilot level 10 dB below the analog channels You are done! March 2010 Proprietary & Confidential

179 Proprietary & Confidential
Screen Annotations Save Ref. File Freq. & dB/Div Control View Sweep Table Trace control (only active when reference is selected) Site File Select Reference Attenuator Sets Forward Pilot Dynamic range P/V freq. range set by Vert. Marker Position Source Level/Slope Controls March 2010 Proprietary & Confidential

180 Proprietary & Confidential
Reverse Sweep Upstream sweep table is automatically Downloaded Communication Icon (lock symbol) will flash yellow, Marker Freqs. & start / stop will update If test point system levels are above 10 dBmV, increase the attenuator setting. If below 0 dBmV, decrease attenuator setting. Set the Transmitter Level for the appropriate Injection Level Peak reference level limited by 3010H setting Note Markers Tilt & P/V Calculated on Vertical Marker Position March 2010 Proprietary & Confidential

181 Referenced Return Sweep
Click REFERENCE, select saved file. RED trace = Live Trace – Reference Trace Automatically adjusts to 2 dB/Div Click A, B, A&B, A-B to toggle Trace (Live, Reference, Both or Difference Traces) Tilt & Peak to Valley calculations based on Vertical Marker Position March 2010 Proprietary & Confidential

182 Bi-directional Test Point
Typical Amp diagrams How to connect Splitter Set the Test Point Loss to 3 dB to compensate for the Splitter or for the Splitter and Test Point loss. March 2010 Proprietary & Confidential

183 Directional Test Points
Reverse EQ Reverse PAD Amp Configurations are Tailored for the Span they serve Diplexers Separate the Upstream & Downstream Path Pads adjust the Flat Gain of Amplifiers Equalizers Compensate for Cable Loss March 2010 Proprietary & Confidential

184 Connecting the 3010R to the 3010H in the System
Fiber Node 3010R Forward Path Fiber Laser Return Path Fiber Receiver RF in RF out The next step in the step is to connect the 3010R to a test point at the fiber node in the field. The slide above shows the connections of the 3010H and the 3010R for return path measurements. The input of the 3010R is connected to a forward path test point. The input is used to receive the communication pilot from the 3010H. The output of the 3010R is connected to a return path insertion point. This point may be a bi-directional test point or a test point made specifically for return path measurements. For more information on the return insertion point, please consult the manuals for the device you are testing . March 2010 Proprietary & Confidential

185 Proprietary & Confidential
What is Ingress? 3010R Return Path with Ingress Ingress refers to interference typically found on the Return Path. Most times it is caused by signals entering the system from the customer drop. When ingress is detected by the 3010H, the it makes a spectrum scan measurement and broadcasts the display data to the field on the forward Pilot. When a 3010R receives the Broadcast Ingress message, it is displayed over F3. Pressing F3 with the message display will allow you to view the spectrum scan measurement from the 3010H Return Path without Ingress The 3010 system has a Ingress detection system. When the 3010H detects ingress at the return pilot frequency, it makes a spectrum scan measurement using the defaults programmed in the spectrum scan mode. The measurement data is broadcast to all the receivers in the field. When a unit in return sweep or return spectrum sees the broadcast ingress message, the Ingress label will appear over F3. If you press F3 when the Ingress label is displayed, you will view the ingress measurement. If you are in Return Spectrum mode, the start and stop frequencies will change to the values programmed in spectrum scan of the 3010H. March 2010 Proprietary & Confidential

186 When Ingress is a Problem.
F3 F3 Pressing F3 will activate the Broadcast Ingress Measurement Indicates Ingress detection at the 3010H A flashing Square Indicates loss of Return Communications The slide above explains different ingress scenarios. * A flashing ‘<‘ indication in the upper right corner of the display indicates normal return sweep mode is working. * A flashing ‘<<‘ indication indicates fast return sweep mode is working. * A flashing indicates no return path communications with the 3010H. * Any solid indicator or absence of an indicator indicates no communications with the 3010H. A flashing symbol indicate the Forward pilot is received from the 3010H A solid symbol indicates no Forward Pilot communications March 2010 Proprietary & Confidential

187 Proprietary & Confidential
The Typical Return To CMTS Receive Port Spare Splitter Leg H L Optical Receiver Fiber Node Optical Receiver H L Optical Receiver Fiber Node Coax Dist.Network H L Fiber Node March 2010 Proprietary & Confidential

188 Proprietary & Confidential
The Funnel H L Fiber Node Optical Receiver Coax Dist.Network Noise from every nook & cranny in the system ends up at the CMTS receive port. March 2010 Proprietary & Confidential

189 You can’t get there from here
The problem could be here … To CMTS Receive Port Spare Splitter Leg H L Optical Receiver Fiber Node Optical Receiver or here … H L Optical Receiver or here … The actual Call might be here Coax Dist.Network H L or the problem could be anywhere in these three nodes. March 2010 Proprietary & Confidential

190 Proprietary & Confidential
Upstream Impairments Common Path Distortion Fast transient noise Ingress March 2010 Proprietary & Confidential

191 Proprietary & Confidential
Upstream Ingress Return Path without Ingress Ingress refers to interference typically found on (but not limited to) the return path. Most ingress comes from the drops. Some sweep systems detect ingress on their return sweep data frequency and broadcast the display data to the field on the forward data carrier for display. Return Path with Ingress March 2010 Proprietary & Confidential

192 Corrosion & Diode Effect
Crystallization occurs and the corrosion creates thousands of small diodes between the two metals Diodes are non-linear devices that can act as frequency “mixers” in a CATV plant March 2010 Proprietary & Confidential

193 Proprietary & Confidential
Frequency Mixing Mixing two frequencies (F1 & F2) will yield four results: 55.25 MHz 61.25 MHz MHz 6.00 MHz F1 F2 F1 + F2 F2 – F1 March 2010 Proprietary & Confidential

194 Common Path Distortion
A corroded connection causes mixing The resulting impedance mismatch also causes reflections The mixing products are reflected right back into the return amplifier. The diplex filter takes out everything above 42 MHz. Corroded Connection 27 Downstream Signals Difference frequencies reflected upstream (~6, 12, 18, 24…) March 2010 Proprietary & Confidential

195 Proprietary & Confidential
CPD in 6 MHz Intervals Because the channels in the forward system are 6 MHz apart, the sum & difference frequencies occur at 6 MHz intervals as well. March 2010 Proprietary & Confidential

196 Other Non-Linear devices
Other non-linear devices can create return path problems Splitters utilizing toroid wound coils can also be non-linear and create mixing problems. A cable modem transmitting at high levels can saturate the toroids forcing them to become non-linear. March 2010 Proprietary & Confidential

197 Spectrum Display Limitations
Scanning Spectrum Analyzers measure only one band of frequencies at any given instant. Frequency Range Where Measurement is Being Made at That Instant Frequencies Stored From Last Pass of Filter March 2010 Proprietary & Confidential

198 Proprietary & Confidential
Fast Intermittents If the spectrum analyzer is at another frequency when the transient appears it will not be displayed. A transient happening at this time will be missed by the filter unless it is still there when the filter comes by again March 2010 Proprietary & Confidential

199 3010 Switch Control Feature
Setup and Operation The Switch Control Feature is only available in firmware versions 5.52 or greater. The following section describes the setup and operation of the switch control function. March 2010 Proprietary & Confidential

200 Switch Control Description
Adds switch driver for AT160x & RPS switches 3010R Adds remote switch control Single node return sweep Requirements Firmware version 5.53 or greater Option 061 turned on (Shown on opening screen) The Switch Control function, formerly called Option 061 adds two switch drivers to the 3010H and remote switch control to the 3010R. This feature is available with firmware version 5.52 or greater and only if option 061 is turned on. Check the opening screen to check the firmware version an the option status on your particular instrument. If you have any questions, please call our support number. March 2010 Proprietary & Confidential

201 Proprietary & Confidential
Features Auto node polling Two switch drivers AT1601 or AT1602 RPS switch Remote switch control Backwards compatible Single node sweep Here is the key features which make up the switch control function. March 2010 Proprietary & Confidential

202 Proprietary & Confidential
AT160x Configuration The AT160x driver supports both the AT1601 or AT1602 switches. The 3010H can control a maximum of 8 switches. This slide shows the cable lash-up. March 2010 Proprietary & Confidential

203 Proprietary & Confidential
Cabling & Equipment Cable H to Switch string Cloning Cable Male 9-pin to Male 9-pin Null Modem Cable - Switch to Switch Straight Through cable Female 9-pin to Male 9-pin Straight Through Combiner Number of ports equals number of switches The cable used to connect the 9-pin RS232 connector to the first switch in the switch string is a Male, 9-pin to Male, 9-pin Null Modem cable. The term ‘Null Modem’ means the connections between pins 2 and 3 are crossed. In other words pin 2 on one connector is attached to pin 3 on the opposite connector. The cable used to connect the switches together is a Female, 9-pin to Male 9-pin, Straight Through cable. In this cable Pin 2 on one end is connected to pin 2 on the other end. For the RF connection, the output of all the switches are combined together using a combiner or a splitter connected backwards with the common port connected to the input of the 3010H. March 2010 Proprietary & Confidential

204 AT160x Programming the Considerations
Each Switch in the string requires a unique address Switch address is used to identify the ports. If you have multiple 3010H/switch configurations in your system you may want to consider using different addresses for every switch in the system. Use the Short Protocol (P1) Use 38,4k baud rate (b2) It is important that all of the switches in the string have a unique address in order for the 3010H to recognize the individual switches. The switches have 64 unique addresses available. The address is also used as part of the node table created by the 3010H when it connects to the switch. In a particular system it may make sense to give each switch a unique address in a given headend or node even if the switch is connected to different 3010H’s, so the technician in the field will be able to tell which 3010H is connected to the switch based on the node table. The 3010H uses the Short Protocol and a baud rate of 38.4k baud. The Protocol and baud rate in the switch must be set to P1 and b2 respectively for the 3010H to recognize the switch. March 2010 Proprietary & Confidential

205 Proprietary & Confidential
Programming the AT160x Press Reset then Local/Remote button Status light will turn yellow Set Switch address, then press Local/Remote button Set Protocol to P1 (Short Protocol), then press Local/Remote button Set Band Rate to b2 (38,4k band), then press Local/Remote button Programming Complete Status light will turn green Programming the AT160x switches is very easy. Just follow the steps listed above. March 2010 Proprietary & Confidential

206 Proprietary & Confidential
3010H 3010H Programming F3 F3 The 3010H requires minimum programming to activate the switch control feature. Go to the bottom of the Return Sweep Setup menu as shown above. At the bottom of the Return Sweep setup screen, highlight “RealView” and press F3. Press “F1” and set the switch driver to “AT160x”. Press Enter. Now press F3 and set the Comms switch control to the last port you would like to poll on the switch. In most cases this will be 16. If you are going to connect forward test points to the switch setup so technician can measure output levels remotely use ports 16 and set the Comms port control to 15. With the port control set to 15, the 3010H will not poll port 16. This will save some polling time. You can now follow the Return Sweep setup instructions as described in the manual. When the 3010H enters the Return Path monitoring or Dual path mode, it will automatically find the Switches connected to the RS232 port, create the node table and begin polling the switches. Switch Driver Port Control March 2010 Proprietary & Confidential

207 Proprietary & Confidential
Switch Drivers ‘AT160x’ Driver AT1601 AT1602 ‘Alt SW1’ Driver RPS Switch There are two user selectable switch drivers in the 3010H. The ‘AT160x’ driver is used for both the AT1601 and AT1602 switches. The ‘Alt SW1’ driver is used for the RPS switch. March 2010 Proprietary & Confidential

208 Proprietary & Confidential
RPS Limitations Only one switch port in a string can be closed at a time. Special switch lash-up required to minimize connection time. There are some limitations when using the ‘Alt SW1’ driver and the RPS switches due to the nature of the RPS switch command set. In a given string of RPS switches, only one port can be close at a time. In order to minimize the polling times, a special equipment lash-up is required. The following slides explains the different lash-up considerations. March 2010 Proprietary & Confidential

209 Proprietary & Confidential
RPS Configuration 1 There are only three Comm Node setting available with the Alt SW1 driver; 4, 7 and 15. In Configuration 1 shown above, the Comm Node is set to 15. This means a tap from all 15 ports are combined together and connected to port 16 of each switch in the string. Using this configuration, the 3010H will poll port 16 of each switch in order to establish communications with field units. After connected, the field units can look at measurements from any port, on any switch, however communications will only be through port 16. March 2010 Proprietary & Confidential

210 Proprietary & Confidential
RPS Configuration 2 In Configuration 2 shown above, the Comm Node is set to 7. This means a tap from first 7 ports are combined together and connected to port 16 and a tap from ports 8 through 14 ports are combined together and connected to port 15 on each switch in the string. Using this configuration, the 3010H will poll ports 15 and 16 of each switch in order to establish communications with field units. After connected, the field units can look at measurements from any port, on any switch, however communications will only be through one of the communications ports. March 2010 Proprietary & Confidential

211 Proprietary & Confidential
RPS Configuration 3 In Configuration 3 shown above, the Comm Node is set to 4. This means a tap from port 1 through 4 are combined and connected to port 16, ports 5 through 8 are combined and connected to port 15, and ports 9 through 12 are combined and connected to port 14 on each switch in the string. Using this configuration, the 3010H will poll ports 14, 15 and 16 of each switch in order to establish communications with field units. After connected, the field units can look at measurements from any port, on any switch, however communications will only be through one of the communications ports. March 2010 Proprietary & Confidential

212 Proprietary & Confidential
3010H Programming AT160x Driver Alt SW1 Driver AT Driver RPS Driver Set to Last Polled port Set to 4, 7 or 15 As described earlier, the driver control is found at the bottom of the Return Sweep Setup menu. If you highlight “RealView” and press F3 you will access the switch control screen. Press “F1” and use the arrow keys to set the switch driver to ‘AT160x’ for AT switches or ‘Alt SW1’ for RPS switches. Press Enter to save the change. Now press F3 and set the Sum Node switch control to 15, 7, or 4 for ‘ALT SW1’ driver or 1 through 16 for the ‘AT160x’ driver. For the AT160x driver, the Comm Node sets the highest port number which will be polled on all switches in the string. Press Enter to save the change and the 3010H switch setup is complete. Select switch driver first, then Comm Node March 2010 Proprietary & Confidential

213 Proprietary & Confidential
3010H Operation F3 F3 The 3010H automatically checks the RS232 port for switches when the Return Path Monitor or Dual Path modes are selected. To select one of these modes, from the Main Menu, press Down arrow, then F1 or F2. If the 3010H fines a switch or switches, it creates a node table and begins polling. The communication status is shown over F3. You will also see the switch sequence on the switch itself. If the 3010H does not see the switch, there will not be a message over F3. Communication Status March 2010 Proprietary & Confidential

214 Proprietary & Confidential
ADD REALWORX SLIDES March 2010 Proprietary & Confidential

215 Troubleshooting DOCSIS Systems
Troubleshooting a DOCSIS system can be challenging. This presentation discusses the different DOCSIS versions and how to troubleshoot from the field technicians point of view. March 2010 Proprietary & Confidential

216 Proprietary & Confidential
History of DOCSIS DOCSIS 1.0 Open standard for high-speed data over cable Best-effort 1st products certified 1999 DOCSIS 1.1 Quality-of-Service (QoS) service flows BPI+ with Certificates Improved privacy with key distribution & encryption processes SNMP for network management security DOCSIS 1.0 is an open standard describing a method to pass high-speed data over a cable network. At the time of it’s creation, there were a number of proprietary systems in place and cable operators saw that it would be advantageous to have multiple companies working on interoperable products. This drove Cable Labs to begin working on the project. The basic protocol uses a best-effort flow control which means system bandwidth is issued on a first come, first served basis similar to the basic flow control used in Ethernet networks. The first DOCSIS modems where certified by Cable Labs in 1999. DOCSIS 1.1 added the missing features to the 1.0 spec. It allows for priority service flows with the Quality-of-Service (QoS) service flow opening the door for timing sensitive applications such as telephony and others. It reduced the thief of service issues by adding BPI+ support and privacy improvements in the encryption processes. Network management security was achieved by adding SNMP support to the system. March 2010 Proprietary & Confidential

217 History of DOCSIS (Cont.)
Goal: greater throughput & robustness on Return Channel Adds 64 & 128 QAM modulation to Return Channels Higher symbol rate up to 5.12 Msps (BW 6.4) Adds Forward Error correction, Trellis coding & programmable interleaving to Return channel Adds multiple modulation & access schemes DOCSIS 3.0 Channel bonding (Increase capacity) Enhanced network security Expanded addressability (IPv6) The goal of DOCSIS 2.0 is to improve the throughput and robustness of the 1.1 spec with respect to the return channel. Early during the implementation of DOCSIS many folks determined that the bandwidth available on the return channel was the limiting factor with respect to throughput. DOCSIS 2.0 improved the data rates on the return channel by adding support for higher level modulation schemes such as 64 and 128 QAM plus higher symbol rates up to 5.12 Msps. In order to use these higher modulation schemes the return path requires a higher level of performance. In order to help correct for linear performance issues, Forward Error correction, Trellis coding and programmable interleaving support was added to the return channel. To continue the theme of backwards compatibility and allow for system operation where system performance is limited, DOCSIS 2.0 allows for multiple modulation and access schemes within the same return channel. DOCSIS 3.0 focus as in DOCSIS 2.0 is to increase capacity. DOCSIS 3.0 achieves this objective by adding channel bonding to the specification both on the forward and return paths. This changes requires increases in hardware cost both at the CMTS and MODEM. However is greatly increases the throughput and capacity of the network. Initial implementation of the specs appear to be in the business to business area which can justify the higher cost of implementation. Enhanced network security was added to the spec to help manage and protect these implementations allow with expanded addressability with support for IPv6. March 2010 Proprietary & Confidential

218 DOCSIS 1.0, 1.1 & 2.0 Reference Architecture
Here is the basic reference architecture used for DOCSIS 1.0 through DOCSIS 2.0 courtesy of the SCTE. As you can see versions 1.1 and 2.0 are enhancements to the basic DOCSIS 1.0 specification. Courtesy of SCTE™ March 2010 Proprietary & Confidential

219 DOCSIS 3.0 Reference Architecture
DOCSIS 3.0 requires changes in the architecture in order to support the additional channels. It adds additional management functionality in order to support higher level services. The main focus of 3.0 is two fold, improved security and much higher data rates which are achieved using bonded channels both on the downstream and the upstream. Additional hardware investment is required to support DOCSIS 3.0 both on the CMTS and the Modem sides of the equation. The HFC system remains basically the same except more spectral bandwidth is required for the additional downstream and upstream channels. Courtesy of Cable Labs® March 2010 Proprietary & Confidential

220 Proprietary & Confidential
Basic DOCSIS Setup Fiber Distribution Coax Dist.Network Drop & Home Wiring H L Fiber Node 10/100 Mb Ethernet DHCP TFTP TOD DNS HTTP ISP C M T S Optical Receiver Up-converter 44 MHz In Out System signals LASER Signal to add’l Laser inputs Combiner Upstream Downstream Network Modem Now let’s consider the basic DOCSIS setup. The system can be broken down into four areas; Downstream, Upstream, the IP Network and the modem and customer equipment. It is the job of the technician to decide which area or areas has the problem when troubleshooting DOCSIS problems. In some cases, the field technician is not responsible to the area which is experiencing the problem. Quickly identifying the area will help determine the best approach to use for eliminating the problem or issue. March 2010 Proprietary & Confidential

221 Proprietary & Confidential
Basic DOCSIS Setup Fiber Distribution Coax Dist.Network Drop & Home Wiring H L Fiber Node 10/100 Mb Ethernet DHCP TFTP TOD DNS HTTP ISP C M T S Optical Receiver Up-converter 44 MHz In Out System signals LASER Signal to add’l Laser inputs Combiner Upstream Downstream IP Network Modem & Cust. Equip. The HFC areas of the system include the Downstream and Upstream paths. In the field these represent the same equipment however in the Headend or Hub the signals take separate paths and have there unique set of issues. The Modem and customer equipment all exist in the customer premise. The responsibility for the equipment in question is dependent on the system strategy. In some cases the cable system owns the equipment and sometimes it does not. The IP Network includes everything after the CMTS, including the CMTS itself. The field technician does not have responsibility for this equipment and in many cases does not have the expertise to completely evaluate the performance. DOCSIS analyzers are extremely helpful in order to determine if this is the area in trouble. March 2010 Proprietary & Confidential

222 Cable Modem Registration
Physical layer (RF plant) - signal transport DOCSIS and IP protocol layers - communicate messaging for modems to come online The next slides illustrate the interaction of these layers in the registration process Cable modem registration required proper communications on all three layers; RF Plant, DOCSIS protocol layer and the IP layer. The next portion of the presentation will go through the registration process used by every modem when it logs on the system. Although the field technician may not think of each step, it can be helpful in determining the problem area when an issue occurs. March 2010 Proprietary & Confidential

223 Proprietary & Confidential
DS Freq. Acquisition CMTS cable modem Next Frequency Sync Broadcast (Minimum one per 200 msec) Scan DS Frequency for a QAM signal No Yes Wait for Sync No Yes The CMTS sends a broadcast sync message approximately every 200 msecs. When the modem is turned on, it looks for the QAM channel on the downstream used by the CMTS. If the modem was on line before, it will begin by checking the last channel used. As you can guess a new modem can take some time before it is able to find the channel used on the system. The DOCSIS data is encapsulated in an MPEG-2 packet, therefore the modem must lock on the QAM channel and search for the PID or Program Identification data. If the well-know PID “1FFE” is found, the modem decodes the MPEG packets and obtains the UCD or Upstream Channel Descriptor. If the correct PID is not found the modem will move to the next QAM channel and check again. When the UCD is found, the modem will look for the MAP Broadcast message. The MAP message include timing and frequency information about the CMTS. Many DOCSIS Analyzers can be programmed so the user can select from a predetermined set of downstream channels. The user should select the channel used by the customer modem to insure it is testing the correct channel. Also, the MAP message contains the valid return frequencies available. Some DOCSIS Analyzers allow the user to select the return channel. Again, the user should select the return channel used by the customer device under test. UCD Broadcast (every 2 sec) No Wait for UCD MAP Broadcast (every 2 ms) Wait for MAP March 2010 Proprietary & Confidential

224 CM Ranging CMTS cable modem RNG-REQ Initial Ranging Request
Sent in Initial Maintenance time Slot Starting at 8 dBmV Using an initial SID = 0 RNG-RSP Ranging Response Contains: Timing offset Power offset Temp SID The modem begins the ranging process by initiating a ranging request to the CMST sent in the initial maintenance time slot starting with a transmit level of 8dBmV and using an initial SID (Session Identifier) equal to 0 then waits for a response from the CMTS. If it does not receive a response, it increments the level by 3 dB, and sends the request again. The modem contiues to icrement the level and send the message until the CMTS responses with a timing offset, power offset and temperary SID to the modem. At that point, the modem sets it’s power level, timing offset and SID approperately and begins to communication with the CMTS. If the modem can not communication on the choosen UCD, it will try another one and begin the ranging process again until it achieves communications with the CMTS. At that point the ranging process is complete. Typically DOCSIS Network Analyzers remember the last UCD used for a given CMTS and it will try to use the same UCD if available in order to reduce the ranging time. Wait for RNG-RSP Increment by 3 dB NO YES Adjust Timing Offset and Power Offset March 2010 Proprietary & Confidential

225 Proprietary & Confidential
DHCP Overview CMTS cable modem Bandwidth Request Use Temp SID (Service ID) MAP Broadcasts DHCP Reply (Offer) DHCP offers an IP address DHCP Discover DHCP Request Acks Initial lP Address and requests Default GW, ToD Server, TOD offset, TFTP Server Addr and TFTP Boot Config File Name DHCP Ack (Response) Contains IP Addr, plus additional information After ranging, the modem is communicating at a basic level with the CMTS. Using the temperary SID the modem receives timing information from the CMTS from the MAP Broadcast message and sends a DHCP Discover message to the DHCP server. The DHCP server answers the message with a DHCP offer IP address. The modem then make a DHCP request acks initial IP address and requests a Default Gateway (GW), ToD Server, TOD offset, TFTP Server Address and TFTP Boot Configuration File Name request. The ToD Server responses with the current Time of Day information. ToD Response Contains Time of Day per RFC (Not NTP) ToD Request March 2010 Proprietary & Confidential

226 Proprietary & Confidential
TFTP & Registration CMTS cable modem TFTP Boot File Transfer DOCSIS config file which contains Classifiers for QoS and schedule, Baseline Privacy (BPI), etc. TFTP Boot Request For ‘Boot File name’ Validate file MD5 Checksum Implement Config Registration Request Send QoS Parameters The modem now sends a TFTP Boot Request to the TFTP server. The server in turn sends a Boot File to the modem based on its provisioning. The Boot File contains the information the modem needs to complete the log-in process such as classifiers for QoS and schedule for Baseline Privacy (BPI), etc….. The validates the file based on the MD5 Checksum, then implements the settings. Next, the modem sends a Registration Request based on the QoS parameters. The CMTS answers the Registration request by assigning a SID to the modem and the modem is on line. Registration Response Contains Assigned SID Modem registered Registration Acknowledge Send QoS Parameters March 2010 Proprietary & Confidential

227 Proprietary & Confidential
BPI+ Added in DOCSIS 1.1 If BPI+ is turned on, the modem will verify it’s authentication Two Certificate types Factory installed Higher level of security Encrypted Certificate obtained by VeriSign and installed by manufacturer Self signed MAC address referenced in Certificate server for authentication BPI+ eliminates MAC address spoofing The entire process is used for all DOCSIS modems. If BPI+ is turned on, during the registration communications the modem with validate its authenticity using its certificate if it has one. There are two types of certificates, factory installed and self signed. Factory certification offer a higher level of security because one modems with an encripted authenticated certificate will be allowed on the network. If Self-Signed certificates are allowed on the network, any device using an authurized MAC address in the Certificate server will be allow on the network. This means that if someone stole a MAC address the MAC could be cloned in another device and it would be able to get onto the network. Allowing self-Signed certificates can be turned on and off as part of the CMTS setup parameters. BPI+ functionality is available in DOCSIS 1.1 or higher modems. March 2010 Proprietary & Confidential

228 CM Registration Summary
Downstream channel search Ranging DHCP ToD TFTP Registration Optional BPI Encryption (DOCSIS 1.1 or higher) If modem contains eMTA, the next slide shows a table of the remaining 25 steps in the eMTA registration process At this point the modem is on line and ready to pass data. Modems which support extended functions such as VoIP contain a MTA must now register the MTA hardware. March 2010 Proprietary & Confidential

229 Proprietary & Confidential
eMTA Registration CM MTA If an MTA is installed the device most complete the remainding 25 steps in order to register the MTA before it is on line. If you consider all of the steps required for a modem to come on line, it is obvious that if you have a major system failure affecting larger numbers of modems, when the system is restored it could take a large amount of time for all the modems to recover. The technician must keep this in mind when trying to test modem functionality after a large outage. Many time it will take hours for the system to get back to normal operations after a repair is made. This condition would also affect the operation of DOCSIS Analzers trying to make modem measurements during this time period. March 2010 Proprietary & Confidential

230 Troubleshooting the Registration Process Downstream
First step in the process Make sure you are connected to the correct DOCSIS channel One channel may be fine and another in trouble Check performance Levels (Remember adjacent channels) MER, BER Linear performance (Freq. response, Group Delay) If the Downstream is fine, Check the Upstream The Downstream must work for the process to begin. If there is a problem with the Downstream DOCSIS channel, the modem will not be able to download the information it needs to log into the network. Here are some things to check to make sure the Downstream is working properly. Most of these parameters can be checked with the DOCSIS Network Analyzer when on line. March 2010 Proprietary & Confidential

231 Troubleshooting the Registration Process Upstream
Check Transmit Level High or Low could indicate a problem Check Frequency & Modulation type May work using QPSK & not 16 or 64 QAM BKER Should be little or no errors Check for Lost or Discarded Packets Lost Packets indicate ingress Discarded Packets indicate congestion May be deceiving There are a number of issues that can affect the performance of the upstream and many times they are intermittent issues. The tests shown here relate to the performance of the upstream. Later in the presentation we will cover a number of test you can use to insure the performance of the upstream. If the modem is working fine and using a higher level modulation scheme, such as 16 or 64 QAM, you can be somewhat confident the HFC network is working properly. If you have an intermittent type problem, the system may work fine for a period of time and then fail. These type problems maybe related to the upstream or they can be related to network problems. March 2010 Proprietary & Confidential

232 Troubleshooting the Registration Process IP Network
Check IP addresses A CPE, or Emulator IP address is required to pass data through the network. Cable IP address is not enough Check Bootfile If default file, you are not provisioned Test ability to pass data through the network Ping – Test connectivity to another device Tracert (Trace route) – Test IP route with transmit times through the network. Throughput – Test the ability to pass data through the network. Browser – Test the ability to connect to a known site through the modem The IP Network is an area most field technicians do not have access to. If there is a problem in the IP Network, the problem is usually passed on to another group. It is important that the technician give as much information about the nature of the problem when the problem is passed on. In the early modem deployments there were a number of times when problems were passed between departments and not repaired because the proper information was not reported. The measurements here will help give each department the tools to determine where the problem exists. March 2010 Proprietary & Confidential

233 Troubleshooting the Registration Process Modem & Customer Equipment
Test ability to pass data through the customer modem Ping – Test connectivity to another device Tracert (Trace route) – Test IP route with transmit times through the network. Throughput – Test the ability to pass data through the network. Browser – Test the ability to connect to a known site If your test equipment is fine, it is probably the customer equipment Customer Equipment Connect customer PC to test instrument May have to reboot PC If not working, maybe bad Net card Substitution is many times used to test the customer equipment and the modem. This can be deceiving because the performance of a device may degrade somewhat as the device warms up to operating temperature. If the Downstream levels are too high or low, a new modem may work when first installed, but after it warms up the noise floor will rise slightly and it can be the difference between it working and not working. This is why it is important to make sure all operating levels on the Downstream and Upstream are correct so that the system has proper headroom. Modem March 2010 Proprietary & Confidential

234 Proprietary & Confidential
CM Network Analyzers Cable Modem Network Analyzer are continually being developed & improved to troubleshoot DOCSIS systems These powerful tools are designed around the premise that if you can quickly determine the source of the problems in a DOCSIS system, you will also save valuable time and un-necessary truck rolls while trying to troubleshoot and repair these problems. All of the tests discussed to this point can be performed by most Cable Modem Network Analyzers. Cable Modem Network Analyzer are powerful tools that help the system operator better maintain the system and eliminate un-necessary truck rolls. In most analysis of system operations the cost of equipping technicians and installers with the proper test equipment is quickly recouped in better system performance, a reduction in truck rolls, a reduction in repair times and happier customers. March 2010 Proprietary & Confidential

235 Digital Network Analyzers
Connect to the CMTS Obtain an IP from the DHCP server Provide Downstream QAM information Provide Lost Packets and BKER information in the upstream Can do Ping, Trace Route and Throughput testing from the Cable Modem or PC emulator Provide the ability to emulate another modem and then step you through the connection process using the customer equipment’s MAC address if BPI+ is turned off. Provide special measurements for extended services such as VoIP and IPTV Here is a list of typical tests performed by a Cable Modem Network Analyzer. March 2010 Proprietary & Confidential

236 Connecting to the Network
Select the Downstream DOCSIS channel Now let’s review how a CM Network Analyzer performs these tests and logs on to a network. Some Analyzers can be programmed to prompt the user to select the downstream DOCSIS channel. This is very important when the system under test has multiple downstream DOCSIS channels. You want to make sure you are using the same channel used by the modem under test. March 2010 Proprietary & Confidential

237 Connecting to the Network
Select UCD (upstream channel descriptor) Likewise some analyzers allow you to select the upstream channel from a list sent to the instrument from the CMTS. Again you should use the same channel used by the modem under test. March 2010 Proprietary & Confidential

238 Proprietary & Confidential
Connecting Process Screen updates as the process is completed & displays the status As the analyzer goes through the registration process the status is displayed on the login screen. It is a good idea to watch the process to see if there are any errors during login. You should note, if you are performing this test immediately after an system outage, you will probably see errors or longer than normal delays when the analyzer tries to contact the DHCP, and TFTP servers. This is normal and is caused by the large number of modems trying to re-login to the network. March 2010 Proprietary & Confidential

239 Proprietary & Confidential
Instrument connected Completed Range & Register Process Modem On-line Win CE Emulator IP MTA IP After the analyzer has completed the process, the modem screen shows the status. Any issues encountered during registration are displayed here. In this case the instrument had to reset and retry once during the connection to the DHCP service. This can be normal depending on network congestion. March 2010 Proprietary & Confidential

240 Downstream/Upstream Info
Analyzer view of Downstream & Upstream parameters. Here are all the measurement information on one screen. The right side of the screen contains the upstream tests and the left side contains the downstream tests March 2010 Proprietary & Confidential

241 Key IP Detail Parameters
IP Address Gateway TFTP Server DHCP server TFTP File name & more The IP detail provides a great deal of IP information that will be valuable to network personnel in troubleshooting network problems. Included from top to bottom of the screen are: *IP Address (as assigned to the analyzer) *CPE IP (as assigned to the analyzer) *Gateway (CMTS) *TFTP Server address *TOD Server address (time of day server not required for connection) *DHCP server (the server that gave the CM it’s IP address. Some systems have more than one.) *TFTP server address March 2010 Proprietary & Confidential

242 Key Downstream Details
Channel Displayed Measurements MER Pre & Post FEC BER Errored Sec Click on a Quadrant to Zoom In By selecting the Downstream button you can view a constellation of the Downstream DOCSIS channel and measure the performance of the channel while you are on line. March 2010 Proprietary & Confidential

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Upstream Detail Upstream transmit level Lost Packets Upstream Block Error Rate Likewise, the Upstream detail lets you view the upstream tests while you are on line. March 2010 Proprietary & Confidential

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Network Testing Upstream Downstream Network Modem Now lets take some time and look at the IP Network. March 2010 Proprietary & Confidential

245 Proprietary & Confidential
The Gateway CMTS converts DOCSIS to Ethernet or some other protocol. C M T S ISP 44 MHz DHCP Up-converter In TFTP 10/100 Mb Ethernet Out Optical Receiver TOD Signal to add’l Laser inputs Of course, the answer is the CMTS. The CMTS converts the DOCSIS traffic to Ethernet traffic. The CMTS is the transition point between the HFC network and the IP Network. DNS System signals Combiner Coax Dist.Network Fiber Node LASER H L HTTP Fiber Distribution Drop & Home Wiring March 2010 Proprietary & Confidential

246 Network Side of the Gateway
ISP – Internet Service Provider(s) DHCP – Dynamic Host Control Protocol Server hands out the IP addresses TFTP – Trivial File Transfer Protocol Server sends the tftp file sometimes called bootp file or bootfile. DNS – Domain Name Server Resolves domain names/IP addresses HTTP – Hypertext Transmission Protocol Server used for download testing TOD – Time of Day Server ISP DHCP TFTP 10/100 Mb Ethernet DNS On the Network side of the CMTS is a number of service blocks. The ISP block refers to the connection from the system operator to the internet. Physically it may be a single server or it may be a number of servers and other equipment. The important point here is that there is an interface, or another gateway in the network to connect DOCSIS modem traffic to the Internet. A few of the other devices we have already talked about such as the DHCP, TFTP and TOD servers. These are all part of the modem management and registration process. Again, they may represent one or many physical servers depending on the network. Two items we have not spoke about is the DNS and HTTP servers. The DNS or Domain Name Server is used to translate URL’s to IP addresses. For example if you type in your message is can be sent to one of four servers with the IP addresses of or or or The internet will determine the best server and route to use. The HTTP server can be installed on the network to perform throughput testing. When an Analyzer in the system does a throughput test, a file is sent to and from this server and the transfer time is measured. This gives you a more accurate view of your system throughput than you can achieve using a server somewhere on the internet. You could have good throughput through your network, and still have a throughput problem when you try to capture files from a server somewhere on the internet. If you offer higher level services such as VoIP, there are a number of other servers and devices that are required on the IP Network to support these applications. This is outside the scope of this presentation and are covered in our VoIP seminars. HTTP CMTS TOD Connection to HFC Network March 2010 Proprietary & Confidential

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Testing the Network Ping Tests Trace Route Tests Throughput Tests Protocol Analysis Digital(DOCSIS) Network Analysis March 2010 Proprietary & Confidential

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How Pings Can Get Lost A CMTS (or any router) will discard any ping packet received in error (upstream errors) A CMTS will discard ping packets when the upstream bandwidth allocation of the originating modem is exceeded DISCARDED PACKETS How do ping packets get lost? There are only two ways a ping packet can be lost in the upstream path. Number One – If the data in a ping packet is corrupted during it’s journey from the CM1000 to the destination address, the destination device (usually the CMTS) will discard it. When a router or any other IP device receives a ping packet that is corrupted, it will know the packet’s condition right away because there is a special checksum attached to the packet that must match the data inside that packet. When a packet takes a “hit”, the checksum no longer matches and the ping packet is discarded as bad. Number Two - Every DOCSIS system sets an upstream “throttle” in terms of upstream data rate. The CMTS acts as the policeman in this case to ensure that the cable modems are not exceeding the upstream “speed limit”. Ping packets are the lowest priority packets in the system. All other data is deemed more important. Consequently, when a router (CMTS) sees that a user is exceeding the upstream limitations, it begins throwing away packets and the ping packets are the first to go. You will see the significance of this when we view the next few slides. The discarding of data packets in a network when a device (switch, router, etc.) is overloaded and cannot accept any incoming data at a given moment. High-level transport protocols such as TCP/IP ensure that all the data sent in a transmission is received properly at the other end March 2010 Proprietary & Confidential

249 Proprietary & Confidential
A Simple DOS ping C:\ping Pinging with 32 bytes of data: Reply from : bytes=32 time<10ms TTL=128 Ping statistics for : Packets: Sent = 4, Received = 4, Lost = 0 (0% loss) Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms (TTL A set maximum amount of time a packet is allowed to propagate through the network before it is discarded.) March 2010 Proprietary & Confidential

250 Proprietary & Confidential
A Simple DOS Tracert C:/tracert Tracing route to SR-INTRA [ ] over a maximum of 30 hops: 1 <10 ms <10 ms <10 ms ms ms ms ms ms ms SR-INTRA [ ] Trace complete. March 2010 Proprietary & Confidential

251 Proprietary & Confidential
Throughput Testing HTTP Server Network PC Any file Care needs to be taken when making throughput comparisons. Processing time of the servers comes into play as well as the type of networks and routers that are involved. March 2010 Proprietary & Confidential

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Network Summary Ping – A packet sent to a specific IP address and returned for test purposes. Trace Route – An offshoot of the Ping test, but provides a trace of the packet through the IP network Throughput – Downloading files to a PC to determine how much average data per second is being transferred March 2010 Proprietary & Confidential

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Downstream Testing Downstream Network Upstream Modem March 2010 Proprietary & Confidential

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Upstream Testing Network Downstream Modem Upstream March 2010 Proprietary & Confidential

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Getting A BKER NE NE PING#1 Ping Packets are numbered consecutively and accounted for as they are received. PING#2 PING#3 March 2010 Proprietary & Confidential

256 Serial Pings & Lost Packets
PING #1 Sent  PING #1 Received PING #2 Sent  PING #2 Received PING #3 Sent  PING #3 Received PING #4 Sent PING #8 Received 4 PACKETS LOST (#4, 5, 6 & 7) March 2010 Proprietary & Confidential

257 Proprietary & Confidential
BLOCK ERROR RATE # Lost Packets Block Error Rate = Total # of Transmitted Packets Block Errors (Lost Packets are used to characterize return path performance) It is possible to “Load Test” the Upstream DOCSIS system using BKER March 2010 Proprietary & Confidential

258 Proprietary & Confidential
Why Test Loading ? Confirm that the customer is actually getting the upstream BW he is paying for Confirm that the BW restrictions are working properly Why should we test loading? Loading is tested for a couple of reasons. First of all, you can confirm that the customer’s account is getting the upstream BW he is paying for. Secondly, you can confirm that the upstream BW restrictions are working properly. Shown above is the main screen of the CM In the lower right hand corner just below the upstream frequency assignment is the modulation type and the upstream QOS (quality of service) throttle number. This is assigned to the modem by the bootfile downloaded during registration. In this case it shows .060 Mbps or 60 kbits/sec is the allocated bandwidth. To test this you would choose a packet size and packet delay setting that would give you slightly more than 60 kbps. If this bandwidth is exceeded, the CMTS should discard the excess ping packets. A full loading chart showing all the combinations of packet size and delay settings with their respective upstream loading is available on our website. March 2010 Proprietary & Confidential

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Loading Calculation 50 bytes Bytes Ping Packet Header & Overhead P A Y L O A D (Packet Size) Load = (50 Bytes + Bytes in Payload) X (8 bits/Byte) (kb/sec) (delay in msec) X msec/sec The upstream “load” is a function of the packet size and the packet delay. Packet size = Header + Payload Packet Delay – How often the packets are transmitted. Very often when we talk about data, we talk about “loading”. In the case of the CM1000, we speak of loading simply the process of sending known amounts of data over a system in order to test the system’s capabilities. By adjusting the size of the ping packets and how often they are transmitted, we can “load” the cable modem’s upstream path to see how the system reacts. Here is a diagram of how a CM1000 ping packet is put together. The basic packet is 50 bytes and if the packet size in the parameter setup is set to zero the entire packet is only 50 Bytes. By adjusting the packet size parameter we can adjust the size of the ping packets being transmitted. The packet size is adjustable from Bytes in 256 Byte increments. The formula shown here will give you the calculated upstream loading for any given packet size and packet delay setting. March 2010 Proprietary & Confidential

260 Proprietary & Confidential
Approximate Loading Delay Size Pkts/min Upstream Load (mSec) (Bytes) (approximate) kb/sec kb/sec kb/sec *Based on a 50 Byte ping packet in addition to the size of the payload. As we said, using the formula we just reviewed, the upstream loading can be calculated. Here are a few examples of settings and the resulting upstream load calculation. It should be noted that during normal operation of the CM1000, we recommend using a small packet size. A packet size of 000 and a packet delay of 20 mSec will be sufficient to diagnose any system noise problems without creating any significant data load on the return system. However, if you would like to run a load test on the upstream, temporarily set the packet delay and packet size of the ping packets to the desired load number. It is possible to create and upstream load as high as 430 kb/sec with these ping packet settings. March 2010 Proprietary & Confidential

261 Upstream Fly in the Ointment
Downstream Network Modem In three out of the four possible problem areas, the trouble can be solved by the service tech handling the call. The Upstream piece of the puzzle is a different story. March 2010 Proprietary & Confidential

262 You can’t get there from here
The problem could be here … To CMTS Receive Port Spare Splitter Leg H L Optical Receiver Fiber Node Optical Receiver or here … H L Optical Receiver or here … The actual Call might be here Coax Dist.Network H L or the problem could be anywhere in these three nodes. March 2010 Proprietary & Confidential

263 Proprietary & Confidential
Diplex Filter C M T S 44 MHz Up-converter In Out Optical Receiver Optical Receiver Low High Common H L DOCSIS Network Analyzer March 2010 Proprietary & Confidential

264 Zero Span/Time Domain Mode
Frequency TIME Amplitude In the Spectrum Mode the horizontal access of the analyzer displays frequency. In the Time Domain mode the analyzer remains on one specified frequency and the horizontal access represents TIME. March 2010 Proprietary & Confidential

265 Upstream Power Measurement
Because upstream Cable Modems transmit in very short bursts, it is difficult to measure their levels. Putting the analyzer in Max Hold will allow you to get an approximation of the CM return levels. Using the Time Domain Mode on the analyzer will allow you to get a very accurate power measurement of your cable modem signals. March 2010 Proprietary & Confidential

266 Proprietary & Confidential
Max Hold Using Max Hold will allow you to get a relative reading on the Cable Modems in the return. This Method is not very accurate, but does provide a good approximation. March 2010 Proprietary & Confidential

267 Measuring Power in TDM mode
Measuring power of cable modems in the return system is a two step process. Step One – Calculate the half-channel bandwidth of the Upstream signal in order to properly setup the analyzer. Step Two – Measure the power using the analyzer average detector and make a bandwidth correction. March 2010 Proprietary & Confidential

268 Calculating Analyzer Center Freq
1. Half Channel Width = Symbol Rate / 2 2. Offset the Center Frequency by 80% of the Half Channel Width: New CF = Original CF - (half Channel Width X 80%) 3. Calculating New CF setting for a 1.6 MHz QPSK signal: Half Channel Width = 1.6MHz (.80)/2 Half Channel Width = .64 MHz = 640 KHz 4. Analyzer CF = MHz – 0.64 MHz 5. Analyzer CF = MHz March 2010 Proprietary & Confidential

269 Proprietary & Confidential
Measuring the Level Set the SPAN to mSec and the Resolution Bandwidth to 1 MHz. Set the trigger level near the top of the signal and adjust to where the preamble is clearly displayed. Use the average detector and place a marker on the preamble Make the bandwidth correction for the measurement. Note: Making the measurement with a noise marker will give you the ability to automatically have the analyzer give you the BW correction. This summary was derived from a detailed Cisco procedure. More detailed information can be found on the Cisco website. March 2010 Proprietary & Confidential

270 Measurement at Preamble
The Measurement Bandwidth is the symbol rate. In this case 1.6 MHz. Adjust for B/W difference between RBW of 1 MHz and the 1.6 MHz measurement BW. Some analyzers will calculate this automatically. BW adjustment= 10 log BW1/BW2 March 2010 Proprietary & Confidential

271 Characterizing the Upstream
Return Path Verification, Test & Troubleshooting Test signal injected in field & measured on analyzer Measure MER, BER, Constellation, Freq. Response, Group Delay March 2010 Proprietary & Confidential

272 Modem & Customer Equip. Testing
Testing the modem, it’s provisioning and the PC connection is the last piece of the troubleshooting puzzle. Downstream Network Upstream Modem March 2010 Proprietary & Confidential

273 Network Analyzer as a CM
ISP CMTS Digital Network Analyzer Customer PC In this case the Network Analyzer is taking the place of the customer’s cable modem. With some units, it is actually possible to “borrow” the MAC address of the customer’s modem and actually emulate that specific modem during the testing process March 2010 Proprietary & Confidential

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PC Emulator ISP CMTS Digital Network Analyzer PC Emulator Using a PC emulation mode, the network analyzer is able to do Ping, Trace Route and Throughput testing from the customer’s premise to any location on the internet. The PC emulation also allows analysis of IP details related to the customers own MAC address March 2010 Proprietary & Confidential

275 Key to CM Troubleshooting
The key to good DOCSIS troubleshooting is to identify which of the four areas need to be worked on. Then as Kenny Rogers said “know when to hold ‘em and know when to fold ‘em”. March 2010 Proprietary & Confidential

276 Architecture of the Future
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Thank You QUESTIONS?? March 2010 Proprietary & Confidential

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Group Delay As different frequencies pass through a Cable System, some will move faster than others t SYSTEM Filters & Traps SYSTEM Filters & Traps 5 MHz 10 MHz 15 MHz 20 MHz 25 MHz 30 MHz 40 MHz 35 MHz 5 MHz 10 MHz 15 MHz 20 MHz 25 MHz 30 MHz 40 MHz 35 MHz 5 MHz 10 MHz 15 MHz 20 MHz 25 MHz 30 MHz 35 MHz 40 MHz T I M E March 2010 Proprietary & Confidential

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Equalizer Taps March 2010 Proprietary & Confidential

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What does sweep do? Checks the Frequency response of the network Checks both forward and return paths Confirms unity gain If the system is flat and levels are correct, distortion will be minimal March 2010 Proprietary & Confidential

281 Setting the Dynamic Range in the 3010H
ENTER Press to save change SCALE The first step in setting up return sweep is to set the dynamic range of the 3010H. The return path measurements will be made at the headend, therefore the Dynamic Range of the measurement is controlled by the attenuator setting in the 3010H. This is accomplished by the full scale setting in the Spectrum scan mode. If you change the full scale setting, you must press ENTER to save the change and return to the measurement screen before you press MENU. We will discuss Ingress later in the presentation, however the spectrum scan screen is also used as the default settings for the Broadcast Ingress measurements. Broadcast Ingress measurements are made when Ingress interferes with the return pilot or when the Broadcast Ingress mode is set to continuous. Rule-of-Thumb: * The full scale should be set high enough so signals on the return path will not overload the receiver, but low enough so you can see the noise floor of the system. * The Start and the Stop frequency should be set to view the entire return path. * Press ENTER to save all changes before pressing MENU to exit the spectrum scan mode when set. F1 F2 F3 F4 March 2010 Proprietary & Confidential


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