Rev.A00 DOCSIS 3.0. CATV Market Dynamics DOCSIS 3 Overview DOCSIS 3 Benefits Preparing for DOCSIS 3 What you need to test How VeEX can help you Troubleshooting

Rev.A00

DOCSIS 3.0

Confidential & Proprietary Information of VeEX Inc. 2

CATV Market Dynamics

DOCSIS 3 Overview

DOCSIS 3 Benefits

Preparing for DOCSIS 3

What you need to test

How VeEX can help you

Troubleshooting Summary

Essential Technical Terms

DOCSIS 3.0

Agenda & Discussion Points


Media Convergence

DOCSIS 3.0

Market Trends

Source: Future services on HFC networks: 33th PIKE Conference, 14 October 2008, Zakopane, Poland

Confidential & Proprietary Information of VeEX Inc. 4DOCSIS 3.0

User Profiles & Applications

Digital Photos

Gaming

MP3 WMV

DVD Blu-ray

SDTV HDTV Mobile

Video

iPod Walkman

You Tube

VODDVR/PVR

Data & VoIP

Home Networks

Web 2.0

Confidential & Proprietary Information of VeEX Inc. 5DOCSIS 3.0

CATV Operators Need DOCSIS 3.0!


Competition is extremely active Telcos are deploying VDSL2, GPON, FIOS and FTTx (USA & Europe)

Consumer’s have an insatiable demand for new services HDTV, VoD, PVR, interactive DTV etc

To meet the growing challenge cable operators have to: Expand network capacity in cost effective and timely manner Evolutionary steps - incremental investments in current technology Revolutionary steps – need to decide if and when to implement a Next Generation HFC

network

CATV Operators Feeling Pressure

DOCSIS 3.0


Verizon Beats Back Cable With YouTube Tilt April 27, 2010 Verizon Communications Inc. (NYSE: VZ) will

soon use FiOS TV's ability to feed in thousands of YouTube videos as a key selling point in TV spots aimed at drawing cable and satellite TV subscribers to its completely fiber-fed platform.

An Ongoing Battle for Customers

DOCSIS 3.0


DOCSIS OverviewDOCSIS 3.0 Benefits


DOCSIS Milestones

DOCSIS 3.0


DOCSIS 3.0 Quick Overview

DOCSIS 3.0


Notes: Downstream bandwidths assuming QAM-256 modulation Upstream bandwidth assuming QAM-64 modulation Maximum synchronization speed and (Maximum usable speed)

DOCSIS Throughput Compared

EuroDOCSISVersion

Date Rates – Annex A

Downstream Upstream

1.x ~ 55.62 (50) Mb/s 10.29 (9) Mb/s

2.0 ~ 55.62 (50) Mb/s 30.72 (27) Mb/s

3.0 (4 Channels) ~ 222.48 (200+) Mb/s 122.88 (108+) Mb/s

3.0 (8 Channels) ~ 444.96 (400+) Mb/s 122.88 (108+) Mb/s

DOCSIS 3.0


DOCSIS 3.0 Channel Bonding

DOCSIS 3.0


Physically the same as DOCSIS 2.0 signals

Consist of multiple QAM signals bonded logically together

Carry data of mutual relevance

Bonded channels can be contiguous or non-contiguous: Contiguous - consist of frequency consecutive signals Non-contiguous - interspersed in the spectrum with other

carriers

MPEG-2 transport for downstream signals

QAM transport for upstream signals

What do we know?

DOCSIS 3.0 Signals

DOCSIS 3.0


DOCSIS 3.0 Preparation


Preparing for DOCSIS 3.0

DOCSIS 3.0


Obtaining the Required Bandwidth

DOCSIS 3.0


Frequency Spectrum Changes

Today 870MHz Soon 1GHz

Reclaiming bandwidth:• Switched Digital Video

• MPEG 4 video

• Analog Video Reclamation

• Higher order modulation

Test requirements:• Downstream expanding to 1GHz

• Bonded channels need verification

• Return Path filling up rapidly impacting traditional sweep and ingress test methods

• In-service testing where possible

DOCSIS 3.0


How much gain?

Upstream Expansion

250Mb/s

500Mb/s

1000Mb/s

DOCSIS 3.0


Operators have strong differences in opinion with regard to options: Solutions are typically driven by specific technical, geographical or local market factors A combination of solutions often determines the preferred option

Expanding HFC Network Capacity

Source: Michiel Peters, TNO - Benelux Chapter SCTE , 15 September 2008, Amsterdam

DOCSIS 3.0


DOCSIS 3.0Plant Qualification & Test Methods


Typical DOCSIS Network

DOCSIS 3.0


Plant Qualification

DOCSIS 3.0


Setup

Upstream Test – Part 1

Configure the Upstream Generator (USG): Frequency, level, modulation, bandwidth, and

symbol rate

Transmit the QAM-64 signal upstream to a CX180+, CX350 or CX380 located in the Headend or Hub.

DOCSIS 3.0


Basic


At the Headend or Hub, check: Digital signal level (dBmV, dBµV) Modulation Error Ratio (MER)

DOCSIS 3.0


Spectrum


At the Headend or Hub, check: Upstream spectrum (5-65MHz) for Ingress,

CPD, and other interference Check below 5MHz and above 65MHz all the

way to 200MHz if possible A QAM-64 signal requires a clean upstream

path!

DOCSIS 3.0


Still Having Problems?

Level and MER look

OK?

A Signal Level Meter (SLM) and Spectrum Analyzer are great application specific tools, but they can be limited in telling you everything you need to know about advanced digital signals

Downstream and upstream (DOCSIS) signals can be impaired by other factors not easily viewed using conventional test methods

Look for the “needle inside the QAM haystack” to figure out what is going on!

DOCSIS 3.0


Advanced

Upstream Testing – Part 4

For the Upstream, you need to check: MER (equalized and un-equalized) Pre and Post FEC Frequency response (in-channel) Group delay (in-channel) Constellation diagram Adaptive equalizer results

DOCSIS 3.0


Advanced

Downstream Testing – Part 5

For the Downstream, you need to check: Digital Power Level MER (equalized and un-equalized) Pre and Post FEC Frequency response (in-channel) Group delay (in-channel) Constellation diagram Adaptive equalizer results

DOCSIS 3.0


Downstream QAM Parameters

BERPre/Post FEC

MER64-QAM: 27 dB min256-QAM: 31 dB min

Constellation

Pre/Post Errorred Seconds (PRES/POES) The number of seconds with at least one corrected codeword

Severely Errorred Seconds The number of seconds with at least one uncorrectable codeword

DOCSIS 3.0


Impairments

Thermal noise is a basic physical phenomenon which cannot be avoided Random voltage variation proportional to temperature, bandwidth and resistance. At room temperature, in 6 MHz bandwidth and 75 ohms circuit, the thermal noise is

approximately -60dBmV. After amplification, the noise level can get much higher. All the other impairments are “human made”, they depend on the design, implementation

and operation of all the elements in the signal chain

It is convenient to group all impairments into 2 categories: Linear distortions and Non-linear distortions.

DOCSIS 3.0


Transmitted phase noise & Low carrier-to-noise ratio

Non-linear distortions (CTB, CSO, XMOD, CPD…)

Linear distortions (micro-reflections, amplitude ripple, group delay)

Severe impedance mismatches aka linear distortions

Improperly aligned or defective amplifiers

In-correct modulation profiles

Incorrect signal levels

In-channel ingress

Data collisions

Laser clipping

What Degrades MER?

DOCSIS 3.0


What MER is Acceptable?

Output of QAM Modulator – 40 dB

Input to Lasers – 39 dB

Output of Nodes – 37 dB

Output of Subscriber Taps – 35 dB

At the input to the subscriber’s receiver – 34 dB

The absolute minimum is 31db

MER is expressed in dB derived as follows:

RMS error magnitude

Average symbol magnitude10 log

DOCSIS 3.0


Downstream PerformancePre/Post FEC BER

What the results are telling you: Level, MER and Constellation are OK Pre/Post FEC BER indicate a problem

What to look for: Interference from a sweep transmitter Downstream laser clipping Up-converter problem in the Headend Loose connections or CPD

DOCSIS 3.0


Notes on FEC

To have an accurate idea of the BER performance you need to know both pre and post FEC bit error rate

Forward error correction (FEC) is a digital error checking system that sends redundant information with the payload so the receiver can repair corrupted data and eliminate the need to retransmit.

By using the same Reed Solomon decoder at the receiving end, bit errors can be detected – these are called Pre-FEC errors

Pre FEC BER is the error rate of the incoming signal prior to being corrected by the FEC circuitry - a minimum of 1x10-7 is expected, but FEC may be able to correct errors as high as 1x10-6.

Post-FEC errors cause poor TV quality or DOCSIS data retransmission

Post FEC Bit errors are not acceptable and should be corrected

The FEC decoder needs a BER of >1x10-6 to operate properly

Both Pre and Post FEC BER need to be verified in order to determine if the FEC circuitry is working to correct errors and if so how hard.

DOCSIS 3.0


Constellation Diagram

QAM – Constellation Diagram

Quadrant 1

Quadrant 2Quadrant 3

Quadrant 4

DOCSIS 3.0


Modulation Error Ratio

MER = 10log (avg symbol power/avg error power)

Average symbolpower

I

Q

Average error power

Source: Hewlett-Packard

I

Q

I

Q

A large “cloud” of symbol points means low MER—this is not good!

A small “cloud” of symbol points means high MER—this is good!

N

jjj

N

jjj

QI

QIMER

1

22

1

22

10log10

DOCSIS 3.0


Forward Path Modulation

ModulationType

Std. Symbol Rate (MHz)

Max data rate(Mbps)

Annex A(8MHz)

QAM64 6.952 41.4

Annex A(8MHz)

QAM256 6.952 55.2(220 max 4 channel bonding)

Annex B(6MHz)

QAM64 5.057 38

Annex B(6MHz)

QAM256 5.361 43(160 max 4 channel bonding)

QAM 64 or QAM 256 are most commonly used

DOCSIS 3.0


Return Path Modulation – DOCSIS

DOCSIS (Data-Over-Cable Service Interface Specifications)Reverse Path / Upstream Data Rate

Standard symbol rate (bandwidth): 1.28 (1.6), 2.56 (3.2), 5.12 (6.4) MHz

DOCSIS Bandwidth(MHz)

Modulationtype

Max data rate(Mbps)

1.0 3.2 QPSK 5.12

1.1 3.2 QPSKQAM16

5.1210.24

2.0 6.4 QAM16QAM64

10.2430.72

3.0 6.4 QAM64QAM128

120(4 channel bonding)

DOCSIS 3.0


Constellation Display

Learn to interpret the constellation display – it tells you a lot of the signal

Symbol points should be small and well-defined

DOCSIS 3.0


Every MPEG2 digital receiver has an Adaptive Equalizer The Equalizer typically cascades two digital filters:

Feed Forward Equalizer (FFE) - reference tap is the last of 16 taps Decision Feedback Equalizer (DFE) - output is fed back to input, 108 taps long

Compensates for Linear distortions (Amplitude imperfections & group delay) The Equalizer uses MER as a tool to adaptively cancel these Linear distortions

The Adaptive Equalizer

DOCSIS 3.0


Adaptive Equalizer Test Functions

Impairment Results

Frequency Response & Group Delay Graphs

Tap Expert

DOCSIS 3.0


What the key measurements are telling you!Hum– Low frequency disturbances of the digital carrier e.g.

switching power supplies

Phase Jitter– Instability of the QAM carrier seen at the demodulator– Phase changes of oscillators e.g. the up-converter– Introduces a back and forth rotation of the

constellation where some symbols will eventually cross the decision boundaries and cause an error in transmission

EVM (Error Vector Magnitude)– A measure of how far constellation points deviate from

their ideal locations. – Ratio of RMS Constellation Error Magnitude to peak

Constellation symbol magnitude

Symbol Rate Error– Should be less than +/- 5pm

Linear Distortions – a closer look (1)

DOCSIS 3.0



What the measurement is telling you!

Frequency Response Frequency response of the digital carrier

Micro-reflections can cause amplitude ripple in the frequency response

Should be less than 3dB (peak-to-peak)

Group Delay Different frequencies travel through the same medium at

different speeds (see supporting slide)

Worse near band edges and diplex filter roll-off areas

Group Delay variation is usually expressed in ns for the Downstream and in “ns / MHz” for the Upstream

Should be < 50ns peak-to-peak

General Notes:• Amplitude and Group Delay responses help visualize the effects of filters, diplexers, traps, suck-outs in the

signal path, from (and including) the QAM modulator up to the point of test.• The frequency span of the calculated responses is directly related to sampling period of the Equalizer

Symbol period. For QAM-64, the span response is 5.05 MHz, while for QAM256 the span is 5.36 MHz

DOCSIS 3.0



What the measurement is telling you!

Echo Margin Echoes are micro-reflections

The tallest vertical bar is the incident signal (reference tap)

Smallest difference between any coefficient and the DOCSIS template defined by CableLabs

Safety margin when getting too close to the “cliff effect”

Should ideally be > 6dB

Equalizer Stress Derived from all the Equalizer coefficients

Indicates how hard the Equalizer is working to cancel out the Linear distortions

Global indicator (the higher the figure, the less stress)

Noise Margin Generally, the lower the MER, the larger the probability of

errors in transmission (Pre-FEC and Post FEC)

Amount of noise that can safely be added to degrade the Equalized MER before losing the signal (cliff effect)

DOCSIS 3.0


Micro-reflection at about 2.5 µs (2500 ns):Assume ~1 ns per ft., 2500/2 = 1250 ft(actual is 1.17 ns per ft: (2500/1.17)/2 = 1068 ft)

Frequency response ripple ~400 kHz p-p:Distance to fault = 492 x (.87/.400) = 1070 ft.

Linear Distortions

DOCSIS 3.0


DOCSIS recommends that the digitally modulated signal’s average power level be set 6 dB to 10 dB below what the visual carrier level of an analog TV channel on the same frequency would be

This ratio should be maintained throughout the entire cable network

Operational RF Levels

DOCSIS 3.0


After link up, power level on forward and return paths are measured.

Step-by-step CM link up process to clearly identify any failed steps

DOCSIS 3.0 CM Emulation Link Up

DOCSIS 3.0


DOCSIS 3.0 CM – IP Tests (1)

Complete server connection status indicates any IP problems

Once the CM is on-line, a full range of IP tests including Ping test can be performed

DOCSIS 3.0


DOCSIS 3.0 CM – IP Tests (2)

Throughput (FTP) Download and Upload should be verified at the CM service location.

Web Test and Web Browser provide bandwidth and visual indications of performance

DOCSIS 3.0


VoIP Expert generates industry standard wave files to verify MOS and R-Factor of upstream and downstream and includes packet jitter, packet loss, and delay.

Real-time of subjective voice quality evaluation (MOS and R-factor) using the TelchemyAlgorithm and test method is provided

DOCSIS 3.0 CM – VoIP Tests (1)

DOCSIS 3.0


Detailed Packet statistics provide a complete insight to transport and IP layer impairments

Jitter performance is checked using the Inter Packet Delay Variation (IPDV) method per RFC3393 recommendations

DOCSIS 3.0 CM – VoIP Tests (2)

DOCSIS 3.0


Ethernet Testing is important to validate business services, E1 circuit emulation or Wireless backhaul applications (E1/T1/IP)

Copper (10/100/1000BaseT) & Fiber (1000BaseX) based Ethernet service should be verified

DOCSIS 3.0 – Ethernet Tests (1)

DOCSIS 3.0


RFC2544, BERT, & Throughput test modes are used to test Ethernet circuits running at the subscriber premise or in the core network at Headend locations

Advanced traffic generation and detailed analysis is used to check and benchmark all types of Ethernet service offered at customer locations.

DOCSIS 3.0 – Ethernet Tests (2)

DOCSIS 3.0


DOCSIS 3.0 Pre-Qualification

DOCSIS 3.0


How Many Testers Do You Need?

CX350 can do

it all

CX380 can do

it all

DOCSIS 3.0


RF Test Checklist

DOCSIS 3.0


Verify correct average power level

Integrated up-converter RF output should be set in the DOCSIS-specified +50 to +61dBmV range

Typical levels are +55 to +58dBmV

Also check BER, MER and constellation

Integrated Up-converter

CMTS

88-860 MHz downstreamRF output

(+50 dBmV to +61 dBmV)

Attenuator(if required)

To headend downstreamcombiner

Troubleshooting

DOCSIS 3.0


Verify correct Power level, BER, MER and Constellation

CMTS downstream IF output

External up-converter IF input

External up-converter RF output

External Up-converter

CMTS

RF upconverter

88-860 MHz downstreamRF output to CATV network

(+50 dBmV to +61 dBmV)

Attenuator44 MHz downstream

IF output(e.g., +42 dBmV +/-2 dB)

44 MHz IF input toupconverter

(typ. +25 dBmV to +35dBmV)

Troubleshooting

DOCSIS 3.0


Check signal levels and BER at downstream laser input and node output

Bit errors present at downstream laser input but not at CMTS or up-converter output may indicate sweep transmitter interference, loose connections or combiner problems

Bit errors at node output but not at laser input are most likely caused by downstream laser clipping

Combiner Output and Fiber Link

DOCSIS 3.0


Troubleshooting Tips

DOCSIS 3.0


Essential Technical Terms to Remember


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.

Phase Noise Jitter (changes in phase) of the oscillators, most likely the up-converter The phase shift or jitter should be < 0.5 degrees

QAM Measurement Terms (1)

DOCSIS 3.0


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 < +/- 5ppm

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 > 6dB


DOCSIS 3.0


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 < 50ns peak-to-peak

Frequency Response Frequency response of the digital carrier Should be < 3dB peak-to-peak

Carrier Offset Carrier frequency test. Should be no more than +/- 25KHz


DOCSIS 3.0

5 MHz

10 MHz

15 MHz

20 MHz

25 MHz

30 MHz

40 MHz

35 MHz

45 MHz

50 MHz

55 MHz

60 MHz

65 MHz


Group Delay - Return Path

5 MHz

10 MHz

15 MHz

20 MHz

25 MHz

30 MHz

40 MHz

35 MHzHFC

(Filters, Taps)

t

HFC(Filters,

Taps)

45 MHz

50 MHz

55 MHz

60 MHz

65 MHz

5 MHz

10 MHz

15 MHz

20 MHz

25 MHz

30 MHz

40 MHz

35 MHz

45 MHz

50 MHz

55 MHz

60 MHz

65 MHz

DOCSIS 3.0


In-Depth Understanding

ECHO MARGINThe Coefficients of the Equalizer will also reveal the presence of an Echo, (a.k.a. micro-reflections). The Equalizer will cancel such an echo, and in doing so, the equalizer coefficient which corresponds to the delay of the echo will be much higher than the surrounding ones, “it sticks out of the grass”. The relative amplitude of this coefficient is an indication of the seriousness of the echo, and its position gives the delay of the echo, hence its roundtrip distance.The Echo Margin is the smallest difference between any coefficients and a template defined by Cablelabs, as a safety margin before getting too close to the “cliff effect”. It is normal to notice relatively high coefficients close to the Reference as this corresponds to the filters in the modulator / demodulator pair and to the shape of QAM signal.

EQUALIZER STRESSThe Equalizer Stress is derived from the Equalizer coefficients and indicate how much the Equalizer has to work to cancel the Linear distortions, it is a global indicator of Linear distortions. The higher the figure, the less stress.

NOISE MARGINWe all know that the lower the MER, the larger the probabilities of errors in transmission (Pre-FEC and then Post-FEC); the MER degrades until errors are so numerous that adequate signal recovery is no more possible (cliff effect). As Noise is a major contributor to the MER, we define Noise Margin as the amount of noise that can be added to a signal (in other words, how much we can degrade MER) before get dangerously close to the cliff effect. Noise is chosen because on the one hand it is always present, and on the other hand it is mathematically tractable. Other impairments, such as an Interferer, are not easily factored into error probabilities.

Linear Distortions

DOCSIS 3.0


In-Depth Understanding

EQUALIZED MER vs. UN-EQUALIZED MERThe MER (Modulation Error Ratio) is the ratio of the QAM signal to Non-Linear distortions of the incoming QAM signal. The MER should have included the Linear distortions to indicate the health of the signal; but the QAM demodulator cannot operate properly without the Equalizer and the Equalizer uses the MER as a tool to adaptively cancel the Linear distortions. Consequently it is convenient to distinguish the MER (non-linear distortions only) from an Un-equalized MER (non-linear and linear distortions), the Un-equalized MER is calculated from the MER and Equalizer Stress.The Un-equalized MER is always worst than the MER. A small difference between the two indicates little Linear distortions, a large difference shows that there are strong Linear distortions. Even if the Linear distortions are cancelled by the Equalizer, we have to keep in mind that the Equalization is a dynamic process as it tracks Linear distortions by trial and error even after converging. The larger the Linear distortions the larger the tracking transients are, hence more probability of transmission error (pre-FEC or Post-FEC BER).

PHASE JITTERPhase Jitter is caused by instability of the carrier of the QAM signal at the demodulator. This instability could be found at the QAM modulator and up-converter or in the QAM receiver (Local Oscillators used in frequency conversions). The phase jitter introduces a rotation of the constellation, where the symbols clusters elongate and get closer to the symbol’s boundary. Eventually some symbols will cross the boundary and cause an error in transmission. The QAM demodulator has a Phase lock loop to track phase variations of the carrier; it tracks easily long term drift as well as some short terms variations (up to 10 or 30 kHz) but it cannot track very fast variations above its loop response. So in a QAM demodulator, the wideband jitter is more damageable than short term jitter.

Linear Distortions

DOCSIS 3.0


Hranac, R. “Digital Troubleshooting, Part 1” Communications Technology, June 2006

www.cable360.net/ct/operations/testing/15092.html

Hranac, R. “Troubleshooting Digitally Modulated Signals, Part 2” Communications Technology, July 2006


Hranac, R. “Linear Distortions, Part 1” Communications Technology, July 2005


Hranac, R. “Linear Distortions, Part 2” Communications Technology, August 2005


Recommended Reading

DOCSIS 3.0

http://www.cable360.net/ct/operations/testing/15092.html





Thank You.Any questions?

DOCSIS 3.0

Documents

Rev.A00 DOCSIS 3.0. CATV Market Dynamics DOCSIS 3 Overview DOCSIS 3 Benefits Preparing for DOCSIS 3 What you need to test How VeEX can help you Troubleshooting