Planning for DOCSIS 3.0 – Bandwidth Management
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Transcript Planning for DOCSIS 3.0 – Bandwidth Management
DOCSIS 3.0 US
Planning & Bandwidth
Management
John Downey, Consulting Network Engineer – CMTS BU
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Co-Sponsor – CCI Systems
Cisco Gold Partner
End-to-end network
services
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Network and headend engineering
Network mapping
Network construction (cable/fiber)
Network maintenance
NOC services
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Co-Sponsor – Todd Gingrass, CCI Systems
Vice President of Network
Technology
14 years at CCI Systems.
Bachelor of Electrical Engineering
degree from Michigan Technical
University
Certifications include Cisco
Certified Network Associate
Routing & Switching (CCNA),
Cisco Certified Design Associate
(CCDA), and Cisco Certified
Internetwork Professional (CCIP)
A member of the Society of Cable
and Television Engineers (SCTE)
and Institute of Electrical and
Electronics Engineers (IEEE)
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Presenter – John Downey, Cisco
20 years in the
data/telecommunications/
networking industry
BS in Electrical Engineering from
Penn State University.
Nine years with Cisco as a
Broadband Network Engineer
presently with the Cable Modem
Termination System (CMTS)
Business Unit.
Certifications include CCNA and
CCCS.
An SCTE member since ’96.
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Agenda
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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Business Objectives
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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ATDMA General Deployment Recommendations
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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US MER(SNR) Issues
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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D3.0 US Issues
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, now test equipment needs to have D3.0
capabilities
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US Frequency and Level Issues
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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Total Power
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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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
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Channel Placement
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 Architectures
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 scheme allows
multiple CMs to transmit same instant in time
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US Load Balance & Isolation Example
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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System Levels Reverse
• 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
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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
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X 38
PIII .5” cable
.40 dB @ 30 MHz
A total design variation of ~14 dB!
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Transmit Level Possibilities
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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Summary
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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Summary (cont)
Long term D3.0 service planning
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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 physical connectivity, not just channel capacity
– May not be advantageous to combine noise to satisfy connectivity
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