DOCSIS 3.0 from a test and measurement point of view Randy Francis Cable Networks Division

DOCSIS 3.0 from a test and measurement point of view

Randy Francis

Cable Networks Division

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

The HFC Pipe is Huge!


New Specifications – DOCSIS 3.0 Interface Specifications (released December 2006)– CPE equipment in development stages( Bronze, Silver, Full)

Downstream data rates of 160 Mbps or higher – Channel Bonding– 4 or more channels

Upstream data rates of 120 Mbps or higher – Channel Bonding– 4 or more channels

Internet Protocol version 6 (IPv6)– IPv6 greatly expands the number of IP addresses

• Expands IP address space from 32 bits to 128 bits • IPv6 supports 3.4×1038 addresses; • Colon-Hexadecimal Format

100% backward compatible with DOCSIS 1.0/1.1/2.0

1 x 256QAM => “up to” ~40Mbps

1 x 64QAM => “up to” ~30Mbps

4923:2A1C:0DB8:04F3:AEB5:96F0:E08C:FFEC

DOCSIS® 3.0 Overview

4 x 256QAM => “up to” ~160 Mbps

4 x 64QAM => “up to” ~120 Mbps


Maximum and (Maximum Usable)DownStream Speeds

Downstream

Version DOCSIS EuroDOCSIS

1.x 42.88 (38) Mbit/s

55.62 (50) Mbit/s

2.0 42.88 (38) Mbit/s

55.62 (50) Mbit/s

3.0 ----------4 channel

171.52 (+152) Mbit/s

+222.48 (+200) Mbit/s

3.0 ----------8 channel

+343.04 (+304) Mbit/s

+444.96 (+400) Mbit/s


Un-Bonded Upstream Data rates

Courtesy Motorola


Channel Requirements

Combines down and upstream channels for added performance

• “Technically” could support 10 bonded down streams.

• Plans are currently for 4 DS and up to 4 u/s channels to be bonded– Do not have to be adjacent to each other – but must be within 60 MHz.

» “Bonded” in data layer – not Physical layer» Each DS channel remains a 6 MHz 256QAM» A DOCSIS 3.0 QAM can be a Primary or Secondary» Primaries carry all info needed for a CM to register» Secondary's do not have registration data – only payload» ALL down streams can be provisioned as primaries but there MUST be

at least 1 primary. – Possible combinations of u/s and d/s– 2x1, 2x2, 3x1, 3x2, 3x3, 4x1, 4x2, 4x3, 4x4– Each provides its own performance capability - and is scalable.


Security

DOCSIS 1.0 had BPI ( Baseline Privacy Interface)– Did not hardware authenticate Cable Modems

DOCSIS 1.1 and 2.0 have BPI+– Digital Certificate based security– No more spoofing MAC addresses

DOCSIS 3.0 adds more enhancements – and the specification is now named “Security”, or BPI/SEC

BPI/SEC encrypts data flows between the CPE and the CMTS– BPI/BPI+ use 56 bit encryption – SEC uses 128 bit

encryption


Pre-Equalization tapsBetter performance under adverse plant enviroment

Docsis 1.1 has 8 tap u/s eq DOCSIS 2.0/3.0 uses u/s24 tap eq Configured in response to the CMTS ranging

request ( RNG-RSP) CMTS says give me a taste – CM responds with a

burst CMTS analyzes response of the burst – and

instructs CM on how to configure its EQ taps ( Equalizer Coefficients)


DOCSIS 3.0 Flavors

BRONZE– Supports downstream bonding– Supports IPv6

SILVER– Supports upstream channel bonding– AES – Advanced Encryption Standard

• More secure than DES – Data Encryption Standard– Support for IPDR

• IP Detail Record• Allows “Consumption Based Billing” – Pay as you use

FULL ( and you thought it would be gold?)– All of Bronze and Silver

Applies to CMTS only – not CM’s CMs from Cisco, Moto, Ambit & Others are now available

– 4x4 bonding only( Texas Instruments silicon– Broadcom announced 8x4 silicon (400Mbs DS/160 Mbs US) in January 2009

This is kinda important – you don’t want to have to upgrade twice. Think hard if 4x4 will be enough!


MSO Rollout of DOCSIS 3.0 Phase 1

– Prepare plant • Physical layer upstream and downstream

– Service turn-on• Downstream Bonding

– Adding additional Downstream carriers» Avoids Node Splitting» Provides load balancing

– Relatively lower number of DOCSIS 3.0 customers on bonded channels– Capacity utilization on secondary/bonded downstreams more physical layer related

• Adding upstream channels– Avoids node splitting– Offers load balancing

• Limited by CMTS’s– Major CMTS vendors are only “Bronze”– Operators are deploying systems using same CMTS & CM vendors

» Cisco & Cisco, Motorola & Motorola, Arris & Arris

Phase 2– Bonding upstream channels– Increasing number of DOCSIS 3.0 users on bonded channels

• Higher capacity utilization and concerns


MSO - Phase 2 Rollouts

Phase 2:– Bonded upstreams

• Major CMTS vendors aren’t planning on production release of bonded upstream support until late CY 2009

– Capacity ramping up – Deployment of DOCSIS 3.0 eMTAs for Voice service

Tests covered by DOCSIS 3.0 solution– Upstream and downstream data-layer performance

• Throughput, packet loss, etc• 100+ MB/s symmetrical

– Breakdown bonded group performance• Isolation of channel issues

DOCSIS 3.0

Hardware

Required


Testing during the Transition

What and How can we toast now?


Sorry – I meant “Test”


Analog Integrity is Still Paramount, Supplemented by QAM Measurements

Majority of “digital” issues involve basic analog maintenance of the RF plant– Levels, including network tilt, must

be optimized beginning at headend– Carrier-to-noise and Hum on analog – Managing Hum has been shown to

improve QAM carrier quality– MER on QAM channels– BER and DQI for intermittent

impairments– Ingress and leakage management


“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 – bad here-good there-problem in between!


Generate Digital

(modulate)

What is Digital?

Source and Destination is digital data– Assign unique patterns of 1’s and 0’s

Transmission path is via an analog QAM carrier – Choice of modulation is the one that optimizes bandwidth

(data versus frequency ‘space’) and resiliency to noise

00 01 10 11 00 01 10 11

Receive Digital

(demodulate)

QAM Analog Carrier

(“QAM Haystack”)


QAM Measurements

Spectrum & Digital Average Power Level MER (Modulation Error Ratio) Pre/Post FEC BER (Bit Error Ratio) QAM Constellation Display QAM “Ingress Under The Carrier” QAM DQI (Digital Quality Index) AGC Stress Group Delay In-Channel Frequency Response Equalizer Stress

– Items in red are really ANALOG impairments measured on a QAM channel


Hum

Low frequency amplitude modulation (<1 kHz) of a carrier when passing through an active or passive component

FCC states that Hum must be < 3%

Caused By:– Power Supply Filter Failure– Bad Solder Connections– Corroded Connectors– Bad power supplies in amplifiers– Earth-loops on coax cables– Bad connection to ground– Earth-loops in headend, interfering with the TV modulators


Hum Modulation Characteristics

Diagnosis - if hum caused by . . .– 60 Hz Component - Check for bad ground connections

– CAREFULLY!– 120 Hz Component - Check DC Power Supply For

Ripple (possible filter capacitor or diode failure)• Can be customer equipment – old TV or VCR or radio

( remember them) power supply

Effect on analog TV picture: one or two bars slowly scroll up the picture

Effect on Digital picture: digital tiling in the picture

Effect on DOCSIS® data: packet loss/slow throughput

Effect on VoIP data: packet loss/robotized voice


Hum Mode is Easy and Non-Intrusive

Tune to analog video carrier, press HUM key

Works on unscrambled analog video carriers only

In-service Hum measurement does not interfere with picture

Some meters have selectable 60Hz, 120Hz and <1,000Hz filters

HUM measurements can be expressed in percentage or dB


AGC Stress

Triggers alarm flag when meter AGC detects signal level change of > .5dB in 1 second of time.

This small but rapid up and down change in level can cause problems with digital set tops boxes and CM’s.

Single channel can be caused by a problem with the QAM modulator

Flagging on multiple channels indicates a problem with the plant trunk/bridger AGC circuits


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


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


Typical Ingress Problem Areas

Taps– Most ingress comes from houses with tap values of

17 dB or less

House Wiring– Drop Cable & F Connectors contribute

approximately ~95% of system ingress problems

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.


“Reverse Spectrum” Install Test

View return spectrum (5 to 42 MHz) and FM band (88 to 108 MHz)

Select peak hold and wait for a few minutes

Re-scan spectrum to confirm that you’ve fixed the ingress problem in the home


Return Path

Taps - Probe the Seizure Screws for Ingress & CPD

If the problem is at the FWD Input and not the FWD Output, then the problem is likely from one of the dropsIf the problem is at

the FWD Output of tap, continue on towards end of line

Forward Path

Disconnect one drop at a time to determine the point of entry


4 Port Tap

Probe the seizure screws for ingress

Taps are made up of a Directional Coupler and Splitters

Disconnect one drop at a time to determine the point of entry

-60

-50

-40

-30

-20

-10

0

10

20

30

40

Center: 25.000 MHzSpan: 40.000 MHzRBW: 300 KHz VBW: 100 KHz Dwell: 400 µS

In-Band Power 10.393 dBmV

-60

-50

-40

-30

-20

-10

0

10

20

30

40

Center: 25.000 MHzSpan: 40.000 MHzRBW: 300 KHz VBW: 100 KHz Dwell: 400 µS

In-Band Power 8.632 dBmV

Seizure screw probe


Equalizer Stress

Digital demodulation receivers utilize adaptive equalizers to negate the effects of signals arriving other than the desired signal.

Signals can arrive ahead of or after the desired signal. In a cable system, the majority of signals are reflections and micro-reflections that arrive after the desired signal.

Cable modems and digital set top boxes must be able to handle pre and post signals at levels defined by DVB standards. If the equalizer is pushed beyond those limits, errors will occur.

By using the Velocity of Propagation, the distance to the source of the reflection can sometimes be located. If the reflections occur before the next upstream amplifier, they are simply amplified and passed downstream thereby eliminating the ability to perform fault detection based on reflection time.

Equalizer stress is used more as a figure of merit for the margin available to the set top box or cable modem.


Equalizer Stress

Signal arriving about 2usec after desired carrier


Micro reflections

Fault here….

Causes energy to reflect back…..

BUT..it has to go thru isolation of directional coupler ….and tap loss

Will we see it at drop?

Level Fault After cable loss, Coupler isolation and tap loss

35dbmv Minor(15 dbRL)

(20)-(4)-(25)-(14)=(-23dBmv)

35dBmv Short/Open (0 RL)

(35)-(4)-(25)-(14)=(-8 dBmv)

A

BC

14


Micro reflections

Fault here….

Causes energy to reflect back…..

B

But its easy to see at non-directional or resistive test points


In Channel Frequency Response

In-Channel Frequency response is amplitude ripple. This means that signals at one frequency are attenuated relative to signals at another frequency. For downstream digital carriers DOCSIS 1.0 specifies a max ripple of 0.5dB in 6MHz. DOCSIS 1.1 has relaxed this specification to 3.0dB in 6MHz.


BER – yet again

A 256QAM channel transmits at a symbol rate of 5M symbols per second

Bit rate = 8 bits per symbol X 5M symbol per second =40M bits per second

Error Incident = Bit rate X BER = Errors Per SecondBER Error Frequency Error Incident 10-12 1 in 1 Trillion bits 25000 secs between errs (6.94 hrs) 10-11 1 in 100 Billion bits 2500 secs between errs (41.67 mins) 10-10 1 in 10 Billion bits 250 secs between errs (4.167 mins) 10-9 1 in 1 Billion bits 25 seconds between errors 10-8 1 in 100 Million bits 2.5 seconds between errors 10-7 1 in 10 Million bits 4 errors per second 10-6 1 in 1 Million bits 40 errors per second 10-5 1 in 100 Thousand bits 400 errors per second 10-4 1 in 10 Thousand Bits 4000 errors per second 10-3 1 in 1 Thousand bits 40000 errors per second


Lets simplify Pre and Post FEC

Imagine some ping pong balls How many balls can you play catch with…….

And not drop one?


BER and intermittent’s…..

Even though digital services (and VoIP) work at MERs of 32, and pre BER of E-7…….THINK…

If you found the cause of that less than normal MER….or improved BER from E-7 to E-8……

Do you think that might have an impact on an intermittent issue?

Lets imagine some ping-pong balls


Why fix -8 and -7 Pre-FEC BER?

You decide to go Bungee Jumping BungJee Jumpee Co says they use 100% more bungee

strands than your weight needs….for safety! You need 50 strands for your weight, so they tell you they

will use 100. When they go to put the bungee on your leg you notice a lot

of broken strands…when you point this out, they say.. Not to worry….you only need 50, right?

ARE YOU JUMPING???


Dots are spread out

showing error

Constellation – a few words

Constellation is Graphic View of MER – But captures bursty impairments better

A constellation displaying significant noise

Dots are spread out indicating high noise and most likely significant errors

– An error occurs when a dot is plotted across a boundary and is placed in the wrong location

Meter will not lock if too much noise present


Gain Compression

If the outer dots are pulled into the center while the middle ones are not affected, the signal has gain compression

Gain compression can be caused by IF and RF amplifiers and filters, up/down converters, modulators, etc

Outer edges pulled in


Phase Noise

Display appears to rotate at the extremes HE down/up converters can cause phase noise Random phase errors cause decreased

transmission margin Caused by transmitter symbol clock jitter Bad LO in meter can cause phase noise

Constellation

Constellation with Phase Noise Zoomed Constellation with Phase Noise

RotationRotation


Coherent Interference

If the accumulation looks like a “donut”, the problem is coherent interference

– CTB, CSO, spurs and ingress

Sometimes only a couple dots will be misplaced

– This is often laser clipping or sweep interference

– Remember I told you about sweep insertion points?

Circular “donuts”


BUT…….

Constellation still doesn’t tell the whole story Constellation is ‘Sampled’

– For each point ( Symbol ) plotted, there are 1000’s that are not.

– So transient intermittents can still be missed.

DQI is a method of showing transients that BER/Consellation views can still miss– Accesses I/Q data before the Constellation sampler


Index from 0 to 10 simplifies readingDerived from Raw I-Q data

DQI responds faster and gives the tech extra margin versus traditional measurements

Momentary events are easily seen in the historical graph

Digital Analysis Tools - DQI


Current Support of Phase 1:Upstream Testing

Most field meters can test upstream signal quality– Range, Packet Loss, VoIP Check, Throughput

PacketLoss and VoIP Check are powerful tools to troubleshoot upstream/downstream BER issues

Upstream QAM generator used out of band with Headend analyzer– Troubleshoot degraded node performance and find problems in plant.

Isolate Packet Loss issues on the RF Plant from the IP Plant. Goal is to have 0% pkt loss Pkt loss on CMTS loop is often due to return path issues


So what will 3.0 test screens look like?

Maybe something like this:

Thank you –

Randy Francis

JDSU

Documents

DOCSIS 3.0 from a test and measurement point of view Randy Francis Cable Networks Division