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

Testing the Network from Headend to the Home

Presented by David Dolnick

JDSU Sales Support Engineer

© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION2

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.


Web BrowsingE-mail

Digital MusicVoIP

Digital Photos

Video on Demand

Video Mail

Online Gaming

Podcasting

Video Blogs

High Definition Video on Demand

All Video on Demand Unicast per Subscriber

Meg

abit

s p

er S

eco

nd

20

10

30

40

50

60

70

80

90

100

Time

Bandwidth Demand is Growing Exponentially!


The HFC Pipe to the Home is Huge!

The BAD news is that ingress from one home can potentially kill upstream services for

hundreds of your subscribers!!!

DOCSIS® 3.0


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.


Electronic Program Guide (EPG)Conditional Access keysService Information (SI)Program Specific Information (PSI)Synchronization

Re-multiplexing

MPEG-PSI

DVB-SI

Digital Video Testing Throughout the Network

QAM

TS(Transport Stream)

TS

Cable distribution(DVB-C)

IP, SDH, ATM, Satellite, DVB-RCS and Terrestrialcontribution

STB(Set Top Box)

SDH

Studio A

Studio Z

IP

Router/GatewayCMTS

DTS-330/RSAM5800/MVP MPEG Probe

Analysis of the feeds and re-

multiplexing

System management

Program management

Subscriber management

ASIQPSK

QA

M

GbE

8VSB



Standalone 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 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 preventingReliable and consistent decoding

Timing affects the ability of the MPEG decoder (QAM or 8VSB) to properly read and Reassemble the video frames.



Analog 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 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 anOscilloscope.

For measuring phase of color carrier to insure proper colors requires theUse of a vectroscope I.e. VM-700


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



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


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)

– Identify Ingress accurately on bad test point or node.– Measurement speed; detects down to 1us burst – Headend equipment detects, alarms, and logs all ingress

H

L

H

L

H

L

H

L

H

LNODE 3

Ingress?!?!

System Sweep Receiver Model 3SR

LEVELTILT SCANSWEEPC/N HUMMODSPECT

FILEAUTO

SETUP

FREQ

CHANENTERFCNCLEAR

helpstatus

alphalight

abc def ghijkl mnopqr

stu vwxyzspace+/-

1 2 34 5 6

7 8 90

x.


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 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 determine Signal 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 frequency Response issues, as well as allowing for balance of the forward plant andSetting unity gain of the reverse amplifiers.


• Less manpower is needed

• Sweeping can reduce the number of service calls

VOD not working

VoIP & Internet not workingChannel 12 video

problems

Cracked hardline found with SWEEP

WHY SWEEP?


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!


A Sweep Finds Problems That Signal Level Measurements Miss

Standing Waves

Roll off at band edges

Misalignment


Testing/Sweeping the HFC Plant

Forward Laser Shelf

SDA-5500

SDA-5510

50 MHz to 860 MHz.

ReverseLaser Shelf

4WAY

CMTS

IPPV

VOD

23 17 11

Subscriber Dwelling

GB

26

17

11

Forward Sweep Response

Reverse Sweep Response



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.


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.



SDA-5500

SDA-5510

50 MHz to 860 MHz.

Forward Laser Shelf

ReverseLaser Shelf

4WAY

CMTS

IPPV

VOD

23 17 11

Subscriber Dwelling

GB

26

17

11

Forward Sweep Response


Examples of Forward sweep

It is important to know which services are digital as opposed to analog servicesAs 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 areBypassed when performing forward sweep

There has been a misconceptions that sweep Places 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.


Balancing Amplifiers - Forward SweepBalancing amplifiers using tilt only

No TerminationLose Face Plate, or crack cable

shield

Node Reference Signal Sweep response with a Resonant FrequencyAbsorption

Sweep response with standing waves

Headend

D = 492*Vp/F

F


Steps to Successful Forward Sweep

1. Take a Tilt Measurement and make certain desired tilt level is set .2. Change EQ value to insure tilt requirement is met.3. Save this measurement into the meters memory, being certain to save

under the proper node or amplifier name.4. 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.

5. Save raw sweep file to allow view of actual sweep display.6. 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.


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 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 display

Step 3. saving the sweep responseAs a reference. Will auto normalize The trace display creating a flatResponse. That will be used as a comparison to next RF active.


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.


Overview

Reverse Sweep Balance and Alignment

SDA-5500

SDA-5510

50 MHz to 860 MHz.

ReverseLaser Shelf

4WAY

CMTS

IPPV

VOD

23 17 11

Subscriber Dwelling

GB

26

17

11

Reverse Sweep ResponseVOD Data Voice

5 MHz to 42 MHz


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.


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.


Creating a Reverse Sweep Plan

VOD Data Voice

5 MHz to 42 MHz


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

Balancing Amplifiers - Reverse Sweep

Telemetry level shown below return sweep trace should read around 0 dBmV if the SDA-5510 is padded properly


X dBmV

Maintain unity gain with constant inputs

X dBmV

X dBmV

X dBmV X dBmV

Optimize the HFC Pipe for Unity Gain

X dBmV

Telemetry = 0 dBmV

Set TP Loss as required

Use the DSAM Field View Optionto inject a CW test signal into various test points and view remote spectrum


Correct pin length,Properly tightened

Pin length too short

Typical connector problems that may result in frequency response issues like suck-outs or roll off

HFC Network Impairments – Frequency Response


Pin length too long

Overtightened seizure screwDamaged pin

This may also hamper the “seating” of the RF module

HFC Network Impairments – Frequency Response


Pin tightened before turningconnector into housing

May result in a broken or twisted pin inside the connector

Center Pin/Seizure Screws

• 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


“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


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


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


Typical Problem Areas

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

low value taps low value taps


NODE

Tracking Down IngressView local spectrum on each return path test point of node to determine which leg

has the source of ingress

Use divide and conquer technique to identify and repair source of ingress


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.

Common problems typically identified in outside plant


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

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

FEDERALCOMMUNICATIONS

COMMISSION


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



Intermittent Connections

Poor craftsmanship on connectors

Loose center seizure screws & fiber connectors

Radial cracks in hard-line coaxial cable

Cold solder joints

Bad accessories


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.


(Gradually poorer C/N)

Effect of Noise on Analog Systems

Broadcast Quality Required FCC Spec


Incorrect Analog Levels

Low analog video level produces noise in the picture

High analog video level produces distortion in the picture


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


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.


eMTA-CABLE MODEM

7 dB TAP

Drop Cable

High Pass Filter

GROUND BLOCK

3-WaySplitter

DIGITAL SET-TOP

House

2-Way Amplifier

Testing the Home for Ingress Contribution

VoIP

OLDER TV SET

Return Equalizer

ONLINE GAMING

WIRELESS LAPTOP

COMPUTOR

ETHERNET

Disconnect drop from tap and check for ingress

coming from customer’s home wiring

INGRESS SPECTRUM MEASUREMENTS

If ingress is detected, scan spectrum at ground

block for ingress


TAP TAP TAP

GB

4WAy

TVTVTVCM/PC

Looking For Forward Ingress in the Subscribers Home

DSAM DSAM

Ingress Free Ingress at 101.7 MHz


TAP TAP TAP

GB

4WAy

TVTVTVCM/PC

Looking For Upstream Ingress from the Subscribers Home

DSAM DSAM

Ingress Free Ingress at 7.25 MHz


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

TAP TAP TAP

GB

4WAy

TVTVTV

DSAM DSAM

CM/PC


Questions?

Thank you for your time!

See Digital in a Whole New Light!

See digital in a whole new light!

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

Documents

Transcript of Testing the Network from Headend to the Home Presented by David Dolnick JDSU Sales Support Engineer.