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 DolnickJDSU Sales Support Engineer
2 AgendaWhat 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 Subscriber10090High Definition Video on Demand8070Video BlogsPodcasting60Megabits per SecondVideo on Demand50Video Mail40Online Gaming30Digital Photos20VoIPDigital Music10Web BrowsingTime
4 The HFC Pipe to the Home is Huge! DOCSIS® 3.0The BAD news is that ingress from one home can potentially kill upstream services for hundreds of your subscribers!!!
5 Testing in the HeadendIt is important to test the content and timing of digital services at various locationsWithin the headend.This includes off-air ATSC (8VSB), Satellite delivered signals (QPSK), GigibitStreams delivered via optical or copper connections, ASI streams within theheadend, and QAM RF modulated signals.Even as we move to digital broadcasts, traditional cable providers will still beDelivering a smaller analog package to support limited basic subscribers.This requires the need for continued traditional RF testing to ensurebalanced levels and acceptable carrier to noise.
6 Digital Video Testing Throughout the Network DTS-330/RSAM5800/MVP MPEG ProbeAnalysis of the feeds and re-multiplexingIP, SDH, ATM, Satellite, DVB-RCS and TerrestrialcontributionCable distribution(DVB-C)STB (Set Top Box)QPSKGbEQAMASIQAMTS(Transport Stream)8VSBTSStudio ASDHRe-multiplexingStudio ZMPEG-PSIDVB-SIRouter/Gateway CMTSIPElectronic Program Guide (EPG)Conditional Access keysService Information (SI)Program Specific Information (PSI)SynchronizationSystem managementProgram managementSubscriber management
7 Testing in the HeadendStandalone Spectrum Analyzers have been the test instrument of choice for the last50 years. They work well when working with traditional RF carriers along with Oscope’sFor testing Baseband signals.As we transition to all digital broadcast services there are many more parametersthat 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 meetingMPEG spec. and that all required MPEG table information is intact.In addition to checking service content we must make certain that there no timingissues within the MPEG stream. Timing is the most common issue preventingReliable and consistent decodingTiming affects the ability of the MPEG decoder (QAM or 8VSB) to properly read andReassemble the video frames.
8 Testing in the HeadendAnalog services require traditional testing to verify level and separation ofVideo and Audio sub-carrier as well as measure CNR and SNR.In addition other measurements such as coherent distortion measurementsAre required these include CSO, CTB, ICFR, and Hum.The above measurements require a spectrum analyzer.Other measurement such as baseband video and audio require anOscilloscope.For measuring phase of color carrier to insure proper colors requires theUse of a vectroscope I.e. VM-700
9 Testing in the HeadendAs 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 pathMost of the ingress comes from home wiring on low value tapsWide variety of aging hardware with many connectorsToday’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 helpSystem operators quickly access issues on the return and very quickly find where issues exist.i.e. (Find and Fix)HLNODE 3Ingress?!?!System Sweep Receiver Model 3SRLEVELTILTSCANSWEEPC/NHUMMODSPECTFILEAUTOSETUPFREQCHANENTERFCNCLEARhelpstatusalphalightabcdefghijklmnopqrstuvwxyzspace+/-123456789x.Identify Ingress accurately on bad test point or node.Measurement speed; detects down to 1us burstHeadend equipment detects, alarms, and logs all ingress
12 Testing the HFC PlantAfter the signals leave the headend they are distributed across the HFC plantTo make certain that are services remain intact we continue to test servicesIn both the downstream (forward services) and the upstream (reverse services)We look at traditional metrics such as CNR and SNR for analog servicesAnd for digital services we also measure MER and BER to determineSignal quality.These same measurements are made on return services that come back fromThe subscribers STB (VOD and IPPV), Cable modem, and MTA.Sweeping the HFC plant is the quickest way to determine any RF frequencyResponse issues, as well as allowing for balance of the forward plant andSetting unity gain of the reverse amplifiers.
13 WHY SWEEP? Less manpower is needed Sweeping can reduce the number of service callsCracked hardline found with SWEEPVoIP & Internet not workingChannel 12 video problemsVOD not working
14 Sweep Verifies Construction Quality Sweep can find craftsmanship or component problems that aren’t revealed with other testsDamaged cablePoor connectorizationAmplifier RF response throughout its frequency rangeGainSlopeLoose 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 MisalignmentStanding WavesRoll off at band edges
16 Testing/Sweeping the HFC Plant ForwardLaser ShelfSDA-5500SDA-551050 MHz to 860 MHz.ReverseLaser Shelf4WAYCMTSIPPVVOD231711SubscriberDwellingGB26Forward Sweep ResponseReverse 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 andFlatness 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 ForwardLaser ShelfForward Sweep Response50 MHz to 860 MHz.SDA-5500ReverseLaser Shelf231711SDA-55104WAYCMTS26IPPVVOD17SubscriberDwelling11GB
20 Examples of Forward sweep It is important to know which services aredigital as opposed to analog servicesAs digital services are carried between4 and 6 dB below the analog servicesSo when digital QAM services are insertedWithin an analog tier they appear to be lowerIn level than the adjacent carriers creatingWhat may appear to be a response issue.Often numerous digital QAM channels areBypassed when performing forward sweepThere has been a misconceptions that sweepPlaces pulses within the active QAM channelsCreating problems with poor MER and BER.Above you will see an absolutely linier responseBetween two channels. This is because thoseServices are not being swept.
21 Lose Face Plate, or crack cable shield Balancing Amplifiers - Forward Sweep Balancing amplifiers using tilt onlyHeadendLose Face Plate, or crack cable shieldNo TerminationD = 492*Vp/FFNode Reference SignalSweep responsewith a Resonant FrequencyAbsorptionSweep responsewith 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 meetRequired 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 displayStep 2. checking the actual responseMaking certain that we run from ourLow channel to our highest channelChecking for frequency suck-outs andAny ingress that may appear.Save snapshot of sweep displayStep 3. saving the sweep responseAs a reference. Will auto normalizeThe trace display creating a flatResponse. That will be used as acomparison to next RF active.
24 Reverse Sweep Balance and Alignment In reverse sweep our goal is to balance the returnFor 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 Overview50 MHz to 860 MHz.SDA-5500ReverseLaser Shelf231711SDA-55104WAYReverse Sweep ResponseVODDataVoice5 MHz to MHzCMTS26IPPVVOD17SubscriberDwelling11GB
26 Steps to Successful Reverse Sweep and Balance When performing reverse sweep it is important to knowthe desired input level to the reverse chip set.This transmit level is based upon manufacturers spec andthe 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” telemetryback at the headend. We will use this number to referenceour gain at each location. Typical window is -15 to +15 dBmV.We must create an accurate channel plan for the reversethat does not interfere with active return services.
27 Reverse SweepThe 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 VODDataVoice5 MHz to MHz
29 Balancing Amplifiers - Reverse Sweep Inject correct “X” level into node test point and then take a sweep referenceAt next amp reverse sweep displays the effects of the network segment between the last amp and this oneTelemetry 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 inputsX dBmVX dBmVX dBmVTelemetry = 0 dBmVSet TP Loss as requiredX dBmVX dBmVX dBmVUse the DSAM Field View Optionto 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 offCorrect pin length,Properly tightenedPin length too short
32 HFC Network Impairments – Frequency Response Pin length too longThis may also hamper the “seating” of the RF moduleOvertightened seizure screwDamaged pin
33 Center Pin/Seizure Screws Pin tightened before turningconnector into housingMay result in a broken or twisted pin inside the connectorA more typical result is the pin gets pushed back into the connector instead of pushing past the seizure screwHappens a lot to housing terminators
34 “Back to the Basics” Troubleshooting Majority of problems are basic physical layer issuesDo a visual inspection of cable, connectors and passives and replace as neededCheck for proper groundingTighten F-connectors per your company’s installation policyBe very careful not to over tighten connectors on CPE (TVs, VCRs, converters etc.) and crack or damage input RFI integrityCheck forward and return RF levels, analog and digitalCheck for reverse ingress coming from homeMost of the test strategy remains the same – divide and conquer technique
35 Back to the BasicsMajority of problems are basic physical layer issuesMost of the tests remain the sameCheck AC powerCheck forward levels, analog and digitalSweep forward & reverse
36 Back to the Basics Check for leakage sources Check for ingress sources Do a visual inspection of cable / connectors / passivesReplace questionable cable / connectors / passivesTighten F-connectors per your company’s installation policyBe 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 tapslow value tapsTapsMost ingress comes from houses off of with low value taps of approximately 17 dB or lessHome WiringDrop Cable, splitters & F Connectors are approximately ~95% of ProblemAmplifiers, 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 IngressView local spectrum on each return path test point of node to determine which leg has the source of ingressNODEUse 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
41 FEDERAL COMMUNICATIONS COMMISSION There are Many Possible Sources of InterferenceOff-Air BroadcastAM Radio StationFM Radio StationTV StationTwo-way Radio TransmittersCitizens Band (CB)Amateur (Ham)TaxiPoliceBusinessAirport/AircraftPaging TransmittersElectrical DevicesDoorbell transformersToaster OvensElectric BlanketsUltrasonic pest controls (bug zappers)FansRefrigeratorsHeating padsLight dimmersTouch controlled lampsFluorescent lightsAquarium or waterbed heatersFurnace controlsComputers and video gamesNeon signsPower company electrical equipmentAlarm systemsElectric fencesLoose fusesSewing machinesHair dryersElectric toysCalculatorsCash registersLightning arrestersElectric drills, saws, grinders, and other power toolsAir conditionersTV/radio booster amplifiersTV setsAutomobile ignition noiseSun lampsSmoke detectorsFEDERAL COMMUNICATIONS COMMISSION
42 Common problems typically identified in outside plant Damaged or missing end-of-line terminatorsDamaged or missing chassis terminators on directional coupler, splitter or multiple-output amplifier unused portsLoose tap faceplates and loose center conductor seizure screwsUnused tap ports not terminated. This is especially critical on lower value tapsUnused drop passive ports not terminatedUse 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 connectorsLoose center seizure screws & fiber connectorsRadial cracks in hard-line coaxial cableCold solder jointsBad 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 pictureHigh analog video level produces distortion in the picture
47 Low QAM Digital levelsLow QAM average power level causes digital signal to degradeThis 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.
51 Testing the Home for Ingress Contribution 7 dB TAPDisconnect drop from tap and check for ingress coming from customer’s home wiringReturn EqualizerHouseDrop CableOLDER TV SETWIRELESS LAPTOPIf ingress is detected, scan spectrum at ground block for ingressDIGITAL SET-TOPCOMPUTORHigh PassFilterVoIPGROUNDBLOCK2-WayAmplifierETHERNET3-WaySplitterONLINE GAMINGeMTA-CABLE MODEMINGRESS SPECTRUM MEASUREMENTS
52 Looking For Forward Ingress in the Subscribers Home TAPTAPTAPIngress FreeIngress at MHzTVGB4WAyTVTVCM/PCDSAMDSAM
53 Looking For Upstream Ingress from the Subscribers Home TAPTAPTAPIngress FreeIngress at 7.25 MHzTVGB4WAyTVTVCM/PCDSAMDSAM
54 How do determine where I need to go to fix problems? TAPTAPTAPTVGB4WAyTVTVCM/PCDSAMDSAM
55 How do determine where I need to go to fix problems? TAPTAPTAPTVGB4WAyTVTVCM/PCDSAMDSAM
56 See Digital in a Whole New Light! Questions?Thank you for your time!