Transcript Planning for DOCSIS 3.0 – Bandwidth Management

DOCSIS 3.0 US
Planning & Bandwidth
Management
John Downey, Consulting Network Engineer – CMTS BU
• Frequency Stacking Levels
What 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.
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• 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
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• 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 recommended
Less 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
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• 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 choices
QPSK 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 affect
Great feature in 1.1 & > CMs, but could mask issues
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• 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
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• MER per US with ability to drill-down for per-CM MER
• Use Return Path monitoring tools
Cisco 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 FEC
If correctable FEC is incrementing, then eventually it will lead to
uncorrectable FEC, which equals packet drops
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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 /
MicroReflections
Ok
Bad
Bad
Eventually Bad
• Ingress cancellation will cancel some CPD
• CPD resembles AWGN when all DSs are digital
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• Frequency Stacking Levels
What is the max output with multiple channels stacked
Is it pwr/Hz & could it cause laser clipping?
• Diplex Filter Expansion to 85 MHz
If 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, & Troubleshooting
Just like DOCSIS 2.0, test equipment needs to have D3.0 capabilities
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• 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 power
Tx 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
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• 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
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• 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
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• Each US channel used for bonding is individual channel
• Transmitters (channels) are separate
Don'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
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• New conundrum raised when fiber run deeper into network
RF 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
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CMTS US0
@ 24 MHz
4-Way
Fiber Optic
Rx 1
Filter
CMTS US2
@ 31 MHz
Amplifier
4-Way
Fiber Optic
Rx 2
CMTS US1
@ 24 MHz
• Attempting to “share” one US port across two other US ports
Can cause isolation issues
Load balance issues (ambiguous grouping)
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• 17 dB at 5 MHz & 32 dB at 1 GHz
• Eliminates max transmit CMs
CS(CEQ) tap
• Eliminates high DS tilt to TV
26
350’
1.5 dB
23
500’
2
17
FEQ
w/ US
pad
600’
2.5
Input 17
Reverse 43 dBmV
transmit
level @ the tap
42
39.5
4
Step
Attenuator
or EQ tap
29
X 38
PIII .5” cable
.40 dB @ 30 MHz
A total design variation of ~14 dB!
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• Running D3.0 CM in low modulation scheme allows higher
power
• Use D3.0 CM in 2.0 mode
Single 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
Pmin = +20 dBmV, 2560 ksym/s
Pmin = +23 dBmV, 5120 ksym/s
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• Cost effective and faster time to market
Decrease 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
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• 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 risk
CMTS, QAM, and CPE
• Account for phy connectivity, not just ch capacity
Not advantageous to combine noise to satisfy connectivity
• Fix Max Tx issues now
Design for tight “bell-curve” (43-48 dBmV), if possible
• Good News – ECR to increase US Tx levels
61 dBmV max, with 3 dB typical
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