Triple-Play Service Testing Carlene Gardner Strategic Marketing Manager JDSU Cable Networks Division For CCTA Training, San Juan PR, August 26, 2009

Triple-Play Service TestingCarlene Gardner

Strategic Marketing ManagerJDSU Cable Networks Division

For CCTA Training, San Juan PR, August 26, 2009

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

Outline

Problems in reverse path– What to look for to check carrier health – What causes performance to degrade

DOCSIS testing– Recap of process to get online– Tips for testing to check where the problem is

VoIP testing– Specific parameters for voice service– Why it is different

Future services

Upstream Test Parameters


Metric: Carrier to Noise, Signal to Noise

Noise


Metric: Carrier to Noise, Signal to Noise

C/N and SNR, versus the noise floor, are somewhat predictive of BER and MER


Metric: MER

Modulation Error Ratio (MER) on downstream QAM carrier is similar to S/N or C/N

MER on upstream QAMs is similar to SNR read at CMTS MER determines how much margin the system has before

failure


Metric: MER

MER math

RMS errormagnitude

Average symbol

magnitude

Indicates how close symbols are to ideal point MER(dB) = 10 x log RMS error magnitude

average symbol magnitude

Upstream channel fails if MER is not better than– QPSK: 18 dB MER– 16 QAM: 24 dB MER– 64 QAM: 27 dB MER


Metric: MER of constellation


Metric: MER degradation due to noise

Symbols cannot reach ideal point due to noise

Ideal points


What Causes MER and BER to degrade?

Noise Ingress in Upstream Cause:

– Often originating from subscriber’s homes, loose RF connectors, or faulty coax cable

– Upstream noise is worse at headend due to “funneling”– A little bit of noise from many locations becomes a lot of noise at the

headend

Effect– When noise ingress gets too high, data symbols start falling outside

their constellation boundaries– The CMTS can no longer correctly determine good data from bad– FEC is no longer able to correct corrupted data packets– The CMTS discards packets with too much data corruption – Web & email traffic will re-transmit and may eventually get through– VoIP traffic is lost forever!



Note that the higher noisefloor causes theMER measurementTo degrade

Noise



Coherent Ingress

Cause– Coherent Ingress are carrier waves or other constant carrier signals

that exist in the HFC network– Ingress: Often originating from subscriber’s homes, loose RF

connectors, or faulty coax cable– Internally-generated impairment: Common Path Distortion (CPD)

Effect– Within a DOCSIS upstream channel, can cause intermittent,

complete data loss or cause a complete DOCSIS outage– Subscribers may complain about a problem that comes and goes

• 24x7 monitoring of ingress is the only way to confidently identify intermittent ingress problems



Compression – Laser / RF Amplifier Cause

– Excessive input levels into an active device causing the laser or amplifier to “clip” or not be able to transmit the highest amplitude voltage signals

– Not rebalancing upstream devices after a change such as adding another DOCSIS channel

Effect– Laser or amplifier clipping causes data loss because the highest

amplitude symbols (bits) are pushed into other symbol decision boundaries

– Data loss can be continuous or sporadic depending upon system and device conditions

– Web traffic can be re-transmitted, but VoIP traffic is permanently lost



Group Delay

Cause– Linear changes in phase of a signal– Inherent difficulty of maintaining even speed of propagation through

multiple devices, long amplifier cascades – Group delay can also occur due to amplitude changes throughout

the upstream band

Effect– Frequencies propagate at different speeds through the HFC plant– Group delay affects cable modem signal quality and thus MER– If group delay is bad enough, the CMTS will be unable to recover

the transmitted signal and data will be lost (<200 nsec/MHz is spec)– Data and VoIP communications will be impacted or lost completely

DOCSIS Testing


DOCSIS Test – Initialization of a Modem

Scan and synchronize to downstream Obtain upstream parameters Range

Send device class Establish IP connectivity Establish time of day Get operational parameters

“Ranging”

“Registration”


Qualify the Drop

Verify receive level at cable modem

MER shows that downstream is clean and clear with margin

BER shows that downstream is clean and clear of impulse noise

Upstream is properly aligned and CMTS has “ideal” receive level

Packet Loss

Throughput


Registration

Full list of registration addresses, Service Identifier (SID) and config file assigned

Error messages detail where a failed test halted, can help locate source of problem


IP or RF?


IP Impairments

Traffic Congestion– CMTS Over-utilization– Switch / Router Over-utilization– Viruses, Worms or just General Killer Apps

Routing Errors– Cable Modem routes– MTA routes– IP Gateways

Provisioning Issues– Subnet Rules– Configuration Files such as TFTP Files– SNMP – BPI & PacketCable Certificates

VoIP Testing


VoIP – Bullet Train Analogy

Ideal World:– Packets like train Cars through a station – 1 at a time,

evenly spaced, and Fast


VoIP – Train Analogy

Real World– VoIP Packets don’t always do what you want…


Metric: MOS Score, R-Factor

Test the HFC Performance– VoIP Quality

• MOS• R-Value

– Processing• Packet Loss• Jitter• Delay


Metrics: Delay, Packet Loss and Jitter

Delay

– Time it takes a packet to ‘transverse’ the network

– Too much delay affects the quality of a call• Over-talk and Echo • Usually an architecture (traffic/capacity) issue• Generally not a HFC issue with equipment such as

amplifiers

C B AD

X-Time

X-Time

Point A Point B

C B AD Network

Aim for 100ms or better



Packet Loss

– Packet did not arrive (Point B) or out of sequence– Worse if it is ‘bursty’, many lost in a row – “lossy”– Can be architecture or physical layer

• Ingress (especially upstream)• Routers over capacity (too full to hold any more)

C B AD

X-Time

∞ -Time

Point A Point B

C B AD Network

Aim for 1% or better



Jitter

– Packets not arriving with the same timing (different from X-Time) – time between packets is different

– You never notice with Data, doesn’t matter how the information arrives, just care that it shows up but VoIP is Real-Time• Key Causes are IP packet routing, IP based equipment

C B AD

X-Time

Point A Point B

C B AD

Slower than XFaster than X

Slower than X

CBADNetwork

Aim for 10ms or better


Use Metrics to Segment HFC and IP layer

Segment HFC and IP impairments– Identify if issues are

occurring in HFC Plant or in the IP network

Check MOS of VoIP over DOCSIS channel

Check VoIP packet statistics– Noise and Ingress on plant

are major causes of Packet Loss


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

COMPUTER

ETHERNET

INGRESS SPECTRUM MEASUREMENTS


Adjust Goals Per Location

Test Criteria Measurement GoalDegradation

Threshold

Delay (1-way) < 100 ms > 150 msJitter < 10 ms > 15 ms

Service Level Test Packet Loss < 1% > 2%R-Value > 70 < 58

MOS > 3.6 < 3MER 30dB(64), 33dB (256) 25dB(64), 28dB(256)

RF PRE-FEC BER 1.00E-09 1.00E-07At Home Rx - Level -5~+5 dBmV <-10dBmV or

>+10dBmVTx - Level 35 ~45 dBmV < 30dBmV or >50dBmV

MER 32dB(64), 35dB (256) 28 dB(64), 31dB(256)RF PRE-FEC BER 1.00E-09 1.00E-07

At Node Freq Response < 4dB > 5dB

Future


DOCSIS® 3.0 – Channel Bonding

256QAM = ~40Mbps (38.8 Mbps)

Individual 256 QAM DOCSIS channel

Versions 1.0/1.1/2.0 used only one channel for upstream and one channel for downstream communications

4 x 256QAM

4 x ~40Mbps = ~160 Mbps

BONDED


Trends in the upstream

Expanding digital environment– Upstream becoming

increasingly crowded– More carriers

More challenging than before– Wider carriers offer a wider

target for interference– Higher modulation has more

sensitivity to ingress


Use constellations to view impairments

Microreflections etc.

Microreflection pattern over time Cloud pattern over time


Back to the Basics

Most problems are still physical layer issues Most of the test strategy remains the same

– Divide and conquer

Check forward and return RF levels– analog and digital

Check for leakage Sweep the forward / reverse to detect issues Replace questionable connectors / passives Tighten F-connectors … but not too tight Robust plant will be ready for the next great thing


Future Services


Thank you!

Carlene Gardner

JDSU Cable Networks Division

Documents

Triple-Play Service Testing Carlene Gardner Strategic Marketing Manager JDSU Cable Networks Division For CCTA Training, San Juan PR, August 26, 2009