DOCSIS 3.0 US Planning & Bandwidth Management John Downey, Consulting Network Engineer – CMTS BU

DOCSIS 3.0 US Planning & Bandwidth Management

John Downey, Consulting Network Engineer – CMTS BU

© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2

• Frequency Stacking LevelsWhat is CM max US output with four channels stacked and do channels have to be contiguous?

• Power/Hz & laser clipping

• Diplex Filter Expansion to 85 MHz?Amplifier upgrades occurring now; Best to make 1 truck roll

Think about diplex filters, line EQs, step attenuators, taps, etc.


• Allow more BW for DOCSIS 1.x & 2.0 CMs

• Limit/reduce more node splits

• Introduce new HSD service of 50 to 100 Mbps

• Allow migration of existing customers to higher tier and DOCSIS 3.0 capability

Better Stat Muxing


• After increasing CW to 6.4 MHz, measure & document unequalized US MER at multiple test points in the plant

Use PathTrak Return Path Monitoring System linecard

Or Sunrise Telecom Upstream Characterization toolkit

• 25 dB or higher Unequalized MER is recommendedLess than 25 dB reduces operating margin

Check US MER as well as per-CM MER

• Pick freq < 30 MHz away from diplex filter group delay

• Make sure latest IOS version is running on CMTS

• Turn on Pre-Equalization


• Increasing ch width from 3.2 to 6.4 keeps same average power for single carrier

SNR drops by 3 dB or more

• Keeping same power/Hz could cause max Tx level from CMs and/or laser clipping/overload

• Equalized vs unequalized MER readings

• Modulation profile choicesQPSK for maintenance, 64-QAM for Data, 16-QAM for VoIP?

Max output for 64-QAM is 54 dBmV

Cab up n power-adjust continue 6

• Pre-EQ affectGreat feature in 1.1 & > CMs, but could mask issues


• Correctable FEC (US & per-CM)

If > 2.5 %: minor alarm

If > 5 %: major alarm

• Uncorrectable FEC (US & per-CM)

If > 0.1 %: minor alarm

If > 1 %: major alarm

• Equalized/PRE-EQ MER(SNR) (US & per-CM)

If < 27 dB: minor alarm

If < 24 dB: major alarm

• Cable Flap-List

D3.0 Modem Diagnostic Log

Can utilize IPDR


• MER per US with ability to drill-down for per-CM MER

• Use Return Path monitoring toolsCisco Broadband Troubleshooter (CBT)

Need analyzer to read < 5 MHz for AM or ham radio ingress

PathTrak to view 5-65 MHz for apparent laser clipping

New PathTrak card reads 0.5 MHz - 85 MHz

• Cable Flap-List monitoring for US or CM issues

• Uncorrectable /Correctable FEC per US with ability to drill-down for per-CM counters

• Bottom line is correctable & uncorrectable FECIf correctable FEC is incrementing, then eventually it will lead to uncorrectable FEC, which equals packet drops


CNR MER(SNR) Corr FEC Uncorr FEC

AWGN Bad Bad Bad Eventually Bad

CW Carrier Bad Ok Ok Ok

Impulse Noise / Laser Clipping

Bad Ok Ok Bad

Group Delay / Micro-Reflections

Ok Bad Bad Eventually Bad

• Ingress cancellation will cancel some CPD

• CPD resembles AWGN when all DSs are digital


• Frequency Stacking LevelsWhat is the max output with multiple channels stacked

Is it pwr/Hz & could it cause laser clipping?

• Diplex Filter Expansion to 85 MHzIf amplifier upgrades are planned for 1 GHz, then pluggable diplex filters may be warranted to expand to 85 MHz on the US

Still must address existing CPE equipment in the field and potential overload

RFoG could be perfect scenario (maybe even 200 MHz split)

• CM must be w-online (requires 1.1 cm file) for US bonding

• Monitoring, Testing, & TroubleshootingJust like DOCSIS 2.0, test equipment needs to have D3.0 capabilities


• Freq assignments 5 to 42, 55, 65, 85 MHz ?

Diplex filters, line EQs, step attenuators, CPE overload

• Max Tx for D2.0 64-QAM for 1 ch is 54 dBmV

• D3.0 US ch max powerTx for D3.0 TDMA

17 - 57 dBmV (32 & 64-QAM)

58 dBmV (8 & 16-QAM)

61 dBmV (QPSK)

Tx for D3.0 S-CDMA

17 - 56 dBmV (all modulations)

• Max Tx per ch for 4 freqs stacked at 64-QAM ATDMA is only 51 dBmV & 53 for S-CDMA



• Was only one US channel present, now up to four US chs transmitting at same time

Possibly 6.4 MHz each; nearly 26 MHz US channel loading

• Lots of power hitting return path fiber optic transmitter

• Probability of laser clipping is increased, especially if using legacy Fabry-Perot (FP) lasers

Good idea to upgrade to Distributed Feedback (DFB) lasers, which have significantly more dynamic range

• Use return path monitoring system capable of looking above 42 MHz to see second and third order harmonics

• Any burst noise above diplex filter (i.e. 42 MHz) coming out of return path receiver is usually indicative of laser clipping


• Blue trace shows case of strong laser clipping

• Green line represents flat US laser noise floor with no clipping

• Note that this US has four US bonded channels


• Each US channel used for bonding is individual channel

• Transmitters (channels) are separateDon't have to be contiguous and can have different physical layer attributes like; modulation, channel width, tdma or scdma, etc.

• Frequencies can be anywhere in US passband and do not need to be contiguous

• It may be wise to keep relatively close so plant problems like attenuation and tilt don’t cause issues

• CM will have some dynamic range to allow specific channels to be a few dB different vs. other channels


• New conundrum raised when fiber run deeper into networkRF over Glass (RFoG)

DOCSIS Passive Optical Networks (DPON)

• May incorporate 32-way optical splitter/combiners. Having a laser Tx in your house combined with 32 other houses feeding 1 Rx in the HE is addressed with lasers timed with the actual traffic from the house; unlike how it is done today where the US laser is on all the time

• US bonding and/or load balancing presents potential issue where an US laser could be transmitting same time as another US laser

• May be acceptable with multiple lasers transmitting same instant in time, if they are carrying different frequencies,

• Will S-CDMA pose same problems? This multiplexing scheme allows multiple CMs to transmit same instant in time


• Attempting to “share” one US port across two other US portsCan cause isolation issues

Load balance issues (ambiguous grouping)

4-Way

4-WayCMTS US0@ 24 MHz

CMTS US1@ 24 MHz

CMTS US2@ 31 MHz

Fiber OpticRx 1

Fiber OpticRx 2

Filter

Amplifier


26 23 17 4350’ 500’ 600’

1.5 dB 2 2.5

17Input

43 dBmV 42 39.5 29

PIII .5” cable.40 dB @ 30 MHz

Reversetransmitlevel @ the tap

A total design variation of ~14 dB!

CS(CEQ) tap

• 17 dB at 5 MHz & 32 dB at 1 GHz• Eliminates max transmit CMs• Eliminates high DS tilt to TV

FEQ w/ US pad

Step Attenuator or EQ tap

38X


• Running D3.0 CM in low modulation scheme allows higher power

• Use D3.0 CM in 2.0 modeSingle frequency on D3.0 CM offers 3 dB higher power

• Using SCDMA with more codes may also allow higher Tx power, but depends on implementation

• Minimum level of 17 dBmV (24?) could cause issues in lab environment or HE test CM

Pmin = +17 dBmV, 1280 ksym/s




• Cost effective and faster time to marketDecrease costs today – deploy DOCSIS 3.0 later with no additional CMTS investment!

• Targeted insertion of D3.0 Leverage existing US chs while adding more US capacity

Load balance 1.x/2.0 and enable D3.0 when needed

Minimizes capex & opex

• Leverage D3.0 bonding for D2.0 tiers & services Better stat-mux efficiency

Improved consumer experience


• Long term D3.0 service planning Insure optimized frequency allocation

Enable seamless upgrade to higher D3.0 tiers

Wire once

Add QAM chs as tiers or service take-rates go up

• End-to-end solution minimizes riskCMTS, QAM, and CPE

• Account for phy connectivity, not just ch capacityNot advantageous to combine noise to satisfy connectivity

• Fix Max Tx issues nowDesign for tight “bell-curve” (43-48 dBmV), if possible

• Good News – ECR to increase US Tx levels61 dBmV max, with 3 dB typical

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DOCSIS 3.0 US Planning & Bandwidth Management John Downey, Consulting Network Engineer – CMTS BU