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Testing the Network from Headend to the Home

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Presentation on theme: "Testing the Network from Headend to the Home"— Presentation transcript:

1 Testing the Network from Headend to the Home
Presented by David Dolnick JDSU Sales Support Engineer

2 Agenda What tools are available for testing in the broadcast headend. Where is testing performed within the headend. Testing the HFC plant (Sweeping the Network). Testing signal quality from Tap to the Home. How to Find and Fix problems from Tap to TV.

3 Bandwidth Demand is Growing Exponentially!
All Video on Demand Unicast per Subscriber 100 90 High Definition Video on Demand 80 70 Video Blogs Podcasting 60 Megabits per Second Video on Demand 50 Video Mail 40 Online Gaming 30 Digital Photos 20 VoIP Digital Music 10 Web Browsing Time

4 The HFC Pipe to the Home is Huge!
DOCSIS® 3.0 The BAD news is that ingress from one home can potentially kill upstream services for hundreds of your subscribers!!!

5 Testing in the Headend It is important to test the content and timing of digital services at various locations Within the headend. This includes off-air ATSC (8VSB), Satellite delivered signals (QPSK), Gigibit Streams delivered via optical or copper connections, ASI streams within the headend, and QAM RF modulated signals. Even as we move to digital broadcasts, traditional cable providers will still be Delivering a smaller analog package to support limited basic subscribers. This requires the need for continued traditional RF testing to ensure balanced levels and acceptable carrier to noise.

6 Digital Video Testing Throughout the Network
DTS-330/RSAM5800/MVP MPEG Probe Analysis of the feeds and re-multiplexing IP, SDH, ATM, Satellite, DVB-RCS and Terrestrial contribution Cable distribution (DVB-C) STB (Set Top Box) QPSK GbE QAM ASI QAM TS (Transport Stream) 8VSB TS Studio A SDH Re-multiplexing Studio Z MPEG-PSI DVB-SI Router/Gateway CMTS IP Electronic Program Guide (EPG) Conditional Access keys Service Information (SI) Program Specific Information (PSI) Synchronization System management Program management Subscriber management

7 Testing in the Headend Standalone Spectrum Analyzers have been the test instrument of choice for the last 50 years. They work well when working with traditional RF carriers along with Oscope’s For testing Baseband signals. As we transition to all digital broadcast services there are many more parameters that must be verified to ensure reliable delivery of quality services. These digital services must be verified at several stages within broadcast headend. They include testing the content to make certain the program provider is meeting MPEG spec. and that all required MPEG table information is intact. In addition to checking service content we must make certain that there no timing issues within the MPEG stream. Timing is the most common issue preventing Reliable and consistent decoding Timing affects the ability of the MPEG decoder (QAM or 8VSB) to properly read and Reassemble the video frames.

8 Testing in the Headend Analog services require traditional testing to verify level and separation of Video and Audio sub-carrier as well as measure CNR and SNR. In addition other measurements such as coherent distortion measurements Are required these include CSO, CTB, ICFR, and Hum. The above measurements require a spectrum analyzer. Other measurement such as baseband video and audio require an Oscilloscope. For measuring phase of color carrier to insure proper colors requires the Use of a vectroscope I.e. VM-700

9 Testing in the Headend As we enter a world of advance interactive services we have to maintain quality return services. Maintaining clean returns that are free of noise and ingress is a big concern as so many of our advance services require an active return to operate. These include VOD, IPPV, Data 3.0, Voice and Interactive TV (ITV). These advance services make monitoring of each return path a necessity for the modern day service provider

10 HFC Networks Combines fiber optics with coaxial distribution network
Return path is more sensitive than the forward path Most of the ingress comes from home wiring on low value taps Wide variety of aging hardware with many connectors Today’s “HFC” networks must be optimized for both forward and reverse performance

11 Testing Returns in the Headend
Return Path Monitoring along with interactive handheld meters has long been the standard to help System operators quickly access issues on the return and very quickly find where issues exist. i.e. (Find and Fix) H L NODE 3 Ingress?!?! System Sweep Receiver Model 3SR LEVEL TILT SCAN SWEEP C/N HUM MOD SPECT FILE AUTO SETUP FREQ CHAN ENTER FCN CLEAR help status alpha light abc def ghi jkl mno pqr stu vwx yz space +/- 1 2 3 4 5 6 7 8 9 x . Identify Ingress accurately on bad test point or node. Measurement speed; detects down to 1us burst Headend equipment detects, alarms, and logs all ingress

12 Testing the HFC Plant After the signals leave the headend they are distributed across the HFC plant To make certain that are services remain intact we continue to test services In both the downstream (forward services) and the upstream (reverse services) We look at traditional metrics such as CNR and SNR for analog services And for digital services we also measure MER and BER to determine Signal quality. These same measurements are made on return services that come back from The subscribers STB (VOD and IPPV), Cable modem, and MTA. Sweeping the HFC plant is the quickest way to determine any RF frequency Response issues, as well as allowing for balance of the forward plant and Setting unity gain of the reverse amplifiers.

13 WHY SWEEP? Less manpower is needed
Sweeping can reduce the number of service calls Cracked hardline found with SWEEP VoIP & Internet not working Channel 12 video problems VOD not working

14 Sweep Verifies Construction Quality
Sweep can find craftsmanship or component problems that aren’t revealed with other tests Damaged cable Poor connectorization Amplifier RF response throughout its frequency range Gain Slope Loose face plates, seizure screws, module hardware……. All of these issues could lead to frequency response problems and major ingress!

15 A Sweep Finds Problems That Signal Level Measurements Miss
Misalignment Standing Waves Roll off at band edges

16 Testing/Sweeping the HFC Plant
Forward Laser Shelf SDA-5500 SDA-5510 50 MHz to 860 MHz. Reverse Laser Shelf 4 W A Y CMTS IPPV VOD 23 17 11 Subscriber Dwelling G B 26 Forward Sweep Response Reverse Sweep Response

17 Testing/Sweeping the HFC Plant
Forward sweep and balance of the RF network is the quickest way to determine deficiencies based upon losses within the copper cable as well as determine noise contribution caused by ingress coming from a variety of sources, both electrical and RF. Reverse sweep and balance, setting unity gain and Flatness of the reverse path allows the operator to identify drop noise and balance the return amplifiers so that they all have the same gain factor. Setting unity gain is important to allow all return devices to transmit at similar RF levels.

18 So how does Sweep work? The idea of forward sweep is to take a reference of all the forward signals in the headend and compare them to what is measured in the field. This means that when viewing forward sweep we are seeing the difference between what was referenced in the headend and what is being measured in the field.

19 Testing/Sweeping the HFC Plant
Forward Laser Shelf Forward Sweep Response 50 MHz to 860 MHz. SDA-5500 Reverse Laser Shelf 23 17 11 SDA-5510 4 W A Y CMTS 26 IPPV VOD 17 Subscriber Dwelling 11 G B

20 Examples of Forward sweep
It is important to know which services are digital as opposed to analog services As digital services are carried between 4 and 6 dB below the analog services So when digital QAM services are inserted Within an analog tier they appear to be lower In level than the adjacent carriers creating What may appear to be a response issue. Often numerous digital QAM channels are Bypassed when performing forward sweep There has been a misconceptions that sweep Places pulses within the active QAM channels Creating problems with poor MER and BER. Above you will see an absolutely linier response Between two channels. This is because those Services are not being swept.

21 Lose Face Plate, or crack cable shield
Balancing Amplifiers - Forward Sweep Balancing amplifiers using tilt only Headend Lose Face Plate, or crack cable shield No Termination D = 492*Vp/F F Node Reference Signal Sweep response with a Resonant Frequency Absorption Sweep response with standing waves

22 Steps to Successful Forward Sweep
Take a Tilt Measurement and make certain desired tilt level is set . Change EQ value to insure tilt requirement is met. Save this measurement into the meters memory, being certain to save under the proper node or amplifier name. Make a forward sweep measurement to view the actual response making certain that there are no major response issues i.e. roll up, roll off, suck outs, ingress. Save raw sweep file to allow view of actual sweep display. Next save the sweep file as a reference sweep file. This will create a flat response which means that any response issues are considered normal for that location. This reference display will be used at the next active downstream so that if both displays are identical then there is no need to perform any other measurements such as tilt. The response will be the same as the previous active.

23 Steps to Successful Forward Sweep
Step 1. change EQ value to meet Required tilt spec 7 to 8 dB at 500 MHz, 10 dB at 750 MHz., 12 dB at 860 MHz, And 14 dB at 1GHz. Save snapshot of tilt display Step 2. checking the actual response Making certain that we run from our Low channel to our highest channel Checking for frequency suck-outs and Any ingress that may appear. Save snapshot of sweep display Step 3. saving the sweep response As a reference. Will auto normalize The trace display creating a flat Response. That will be used as a comparison to next RF active.

24 Reverse Sweep Balance and Alignment
In reverse sweep our goal is to balance the return For flatness and adjust the return gain so that it is the same at every housing (unity gain). Setting the reverse amplifiers at all locations to the same gain allows all return devices to transmit at the same relative RF level i.e. cable modems, MTA’s, STB’s. You must take into account return band noise as the CMTS will set CM’s transmit level to be 29 db c/n or better, therefore high noise floor will cause modems and MTA’s to transmit at high RF levels.

25 Reverse Sweep Balance and Alignment
Overview 50 MHz to 860 MHz. SDA-5500 Reverse Laser Shelf 23 17 11 SDA-5510 4 W A Y Reverse Sweep Response VOD Data Voice 5 MHz to MHz CMTS 26 IPPV VOD 17 Subscriber Dwelling 11 G B

26 Steps to Successful Reverse Sweep and Balance
When performing reverse sweep it is important to know the desired input level to the reverse chip set. This transmit level is based upon manufacturers spec and the design of the plant. (Typically this will be between 17 and 21 db at the chip set). When we insert we try to adjust for “0 dB” telemetry back at the headend. We will use this number to reference our gain at each location. Typical window is -15 to +15 dBmV. We must create an accurate channel plan for the reverse that does not interfere with active return services.

27 Reverse Sweep The first step for a working reverse sweep is to build a reverse channel plan in the headend unit that does not interfere with active services. This channel plan will be used to tell the meter in the field what frequencies to transmit back on the return. It is important that a technician does not inject carriers at the same frequencies as active services or anyone using these services on that path will be offline.

28 Creating a Reverse Sweep Plan
VOD Data Voice 5 MHz to MHz

29 Balancing Amplifiers - Reverse Sweep
Inject correct “X” level into node test point and then take a sweep reference At next amp reverse sweep displays the effects of the network segment between the last amp and this one Telemetry level shown below return sweep trace should read around 0 dBmV if the SDA-5510 is padded properly

30 Optimize the HFC Pipe for Unity Gain
Maintain unity gain with constant inputs X dBmV X dBmV X dBmV Telemetry = 0 dBmV Set TP Loss as required X dBmV X dBmV X dBmV Use the DSAM Field View Option to inject a CW test signal into various test points and view remote spectrum

31 HFC Network Impairments – Frequency Response
Typical connector problems that may result in frequency response issues like suck-outs or roll off Correct pin length, Properly tightened Pin length too short

32 HFC Network Impairments – Frequency Response
Pin length too long This may also hamper the “seating” of the RF module Overtightened seizure screw Damaged pin

33 Center Pin/Seizure Screws
Pin tightened before turning connector into housing May result in a broken or twisted pin inside the connector A more typical result is the pin gets pushed back into the connector instead of pushing past the seizure screw Happens a lot to housing terminators

34 “Back to the Basics” Troubleshooting
Majority of problems are basic physical layer issues Do a visual inspection of cable, connectors and passives and replace as needed Check for proper grounding Tighten F-connectors per your company’s installation policy Be very careful not to over tighten connectors on CPE (TVs, VCRs, converters etc.) and crack or damage input RFI integrity Check forward and return RF levels, analog and digital Check for reverse ingress coming from home Most of the test strategy remains the same – divide and conquer technique

35 Back to the Basics Majority of problems are basic physical layer issues Most of the tests remain the same Check AC power Check forward levels, analog and digital Sweep forward & reverse

36 Back to the Basics Check for leakage sources Check for ingress sources
Do a visual inspection of cable / connectors / passives Replace questionable cable / connectors / passives Tighten F-connectors per your company’s installation policy Be very careful not to over tighten connectors on CPE (TVs, VCRs, converters etc.) and crack or damage input RFI integrity

37 Typical Problem Areas Taps Home Wiring
low value taps low value taps Taps Most ingress comes from houses off of with low value taps of approximately 17 dB or less Home Wiring Drop Cable, splitters & F Connectors are approximately ~95% of Problem Amplifiers, hard line cable and the rest of the system are a small percentage of the problem if a proper leakage maintenance program is performed

38 Tracking Down Ingress View local spectrum on each return path test point of node to determine which leg has the source of ingress NODE Use divide and conquer technique to identify and repair source of ingress

39 Common problems typically identified in outside plant
Kinked or damaged cable (including cracked cable, which causes a reflection and ingress). Defective or damaged actives or passives (water-damaged, water-filled, cold solder joint, corrosion, loose circuit-board screws, etc.). Cable-ready TVs and VCRs connected directly to the drop. (Return loss on most cable-ready devices is poor.) Some traps and filters have been found to have poor return loss in the upstream, especially those used for data-only service.

40 Common problems typically identified in outside plant

There are Many Possible Sources of Interference Off-Air Broadcast AM Radio Station FM Radio Station TV Station Two-way Radio Transmitters Citizens Band (CB) Amateur (Ham) Taxi Police Business Airport/Aircraft Paging Transmitters Electrical Devices Doorbell transformers Toaster Ovens Electric Blankets Ultrasonic pest controls (bug zappers) Fans Refrigerators Heating pads Light dimmers Touch controlled lamps Fluorescent lights Aquarium or waterbed heaters Furnace controls Computers and video games Neon signs Power company electrical equipment Alarm systems Electric fences Loose fuses Sewing machines Hair dryers Electric toys Calculators Cash registers Lightning arresters Electric drills, saws, grinders, and other power tools Air conditioners TV/radio booster amplifiers TV sets Automobile ignition noise Sun lamps Smoke detectors FEDERAL COMMUNICATIONS COMMISSION

42 Common problems typically identified in outside plant
Damaged or missing end-of-line terminators Damaged or missing chassis terminators on directional coupler, splitter or multiple-output amplifier unused ports Loose tap faceplates and loose center conductor seizure screws Unused tap ports not terminated. This is especially critical on lower value taps Unused drop passive ports not terminated Use of so-called self-terminating taps (4 dB two port; 8 dB four port and 10/11 dB eight port) at feeder ends-of-line. Such taps are splitters, and do not terminate the line unless all F ports are properly terminated

43 Intermittent Connections
Poor craftsmanship on connectors Loose center seizure screws & fiber connectors Radial cracks in hard-line coaxial cable Cold solder joints Bad accessories

44 Qualifying the Subscriber Drop and Residence
Many tools exist for qualifying both the subscriber drop and in-house wiring. A quick test of service quality across a fair number of channels both analog and digital can reveal issues within the home such as poor craftsmanship. Poor connectorization spun-out F81 connectors in wall plates bad passive devices (splitters and GB’s), bad spans of cable, exposed sheath. Can all be causes of ingress that can affect a subscribers quality of service, by creating poor C/N, MER, BER’s.

45 Effect of Noise on Analog Systems
(Gradually poorer C/N) Broadcast Quality Required FCC Spec

46 Incorrect Analog Levels
Low analog video level produces noise in the picture High analog video level produces distortion in the picture

47 Low QAM Digital levels Low QAM average power level causes digital signal to degrade This causes tiling and intermittent or complete loss of high speed Internet access

48 Home Certification Testing
Testing a variety of analog and digital services, including parameters such C/N, MER and BER., can reveal service quality or poor in-house wiring issues. Additionally testing of DOCSIS channel can tell us if we can support data and voice services at the subscribers residence on the drop tested.

49 Home Certification Testing

50 Home Certification Testing

51 Testing the Home for Ingress Contribution
7 dB TAP Disconnect drop from tap and check for ingress coming from customer’s home wiring Return Equalizer House Drop Cable OLDER TV SET WIRELESS LAPTOP If ingress is detected, scan spectrum at ground block for ingress DIGITAL SET-TOP COMPUTOR High Pass Filter VoIP GROUND BLOCK 2-Way Amplifier ETHERNET 3-Way Splitter ONLINE GAMING eMTA-CABLE MODEM INGRESS SPECTRUM MEASUREMENTS

52 Looking For Forward Ingress in the Subscribers Home
TAP TAP TAP Ingress Free Ingress at MHz TV G B 4 W A y TV TV CM/PC DSAM DSAM

53 Looking For Upstream Ingress from the Subscribers Home
TAP TAP TAP Ingress Free Ingress at 7.25 MHz TV G B 4 W A y TV TV CM/PC DSAM DSAM

54 How do determine where I need to go to fix problems?

55 How do determine where I need to go to fix problems?

56 See Digital in a Whole New Light!
Questions? Thank you for your time!

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