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© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 1
HFC Plant Optimization for D3.0
John J. DowneyConsulting Network Engineer
Cisco Systems
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 2
ATDMA General Deployment Recommendations After increasing channel width to 6.4 MHz, measure &
document US MER (unequalized would be best)– 25 dB or higher Unequalized MER is recommended
– Check US MER as well as per CM MER
Document unequalized MER with test equipment at multiple test points in plant– PathTrak Return Path Monitoring System linecard
– Sunrise Telecom Upstream Characterization toolkit
– Trilithic
Pick freq < 30 MHz away from diplex filter group delay
Turn on Pre-Equalization– Can exclude specific Mac or OUI
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 3
US MER(SNR) Issues Increasing ch width keeps same average power
– Doubling ch width will drop MER by 3 dB or more
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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 4
4
Pre-EQ
Upstream 6.4 MHz bandwidth 64-QAM signal
After Adaptive EQ:DOCSIS 2.0’s 24-tap EQ—was able to
compensate for nearly all in-channel tilt (with no change in digital channel power). Result: No correctable or uncorrectable FEC errors and the CMTS’s reported US MER (SNR)
increased to ~36 dB.
Before Adaptive EQ:Substantial in-channel tilt caused correctable
FEC errors to increment. CMTS’s reported US MER (SNR) was 23 dB.
4
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 5
Post-Deployment Troubleshooting
MER per US with ability to drill-down for per-CM MER
Use US monitoring tools like PathTrak or Cisco Broadband Troubleshooter (CBT) to view 5-65 MHz for laser clipping– Need analyzer to read < 5 MHz for AM or ham radio ingress
– New PathTrak card reads 0.5 MHz - 85 MHz & MacTrak
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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 6
CBT Display
66
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 7
Impairment Increase vs Reporting
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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 8
Pre-eq Coeff Direct Load
CMs that drop > 3 dB MER in one SM period get direct load
CMTS support for Type 9 TLVs for DOCSIS 2.0 &> CMs
DOCSIS 1.1 CMs in this state re-register
Following message types added to "sh cab modem verbose" – Pre-Equalization Counters : 1205 good, 0 scaled, 24 impulse– Equalizer Coeffs Direct Load : 1 direct coeff loads
• Significant change in freq response may create scaled count• When CMTS decides to return CM’s EQ taps to known state
without direct load, an impulse value is sent• Each time Type 9 TLV is sent to CM, direct load counter will
increase by 1• When CM goes offline, counters are zeroed
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 9
Determining per-CM Pre-EQ Taps
Poll pre-eq tap MIB directly from CM:– Raw values polled to determine red, yellow, green
Cablelabs Proactive Network Maintenance (PNM)
Charter’s “Node Slayer”
Comcast has “Scout Flux”
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 10
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 field & 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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 11
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 single ch max power– 57 dBmV (32 & 64-QAM)
– 58 dBmV (8 & 16-QAM)
– 61 dBmV (QPSK)
Max Tx per ch for 4 freqs stacked at 64-QAM ATDMA is only 51 dBmV & 53 for S-CDMA– When stacking, level will not change unless max is reached
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 12
Channel Placement
Each US channel used for bonding is individual channel
Transmitters (channels) are separate– Can have different settings; modulation, ch width, tdma or scdma,
etc.
Frequencies do not need to be contiguous
Wise to keep relatively close so attenuation and tilt don’t cause issues
CMs have some dynamic range to allow few dB difference between channels
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 13
Sample Upstream Spectrum Usage
# From To BW Modulation Style PrimaryUsage
10 61.4 64.6 3.2 64-QAM ATDMA D3.0
9 54.8 61.2 6.4 64-QAM ATDMA D3.0
8 48.2 54.6 6.4 64-QAM ATDMA D3.0
7 41.6 48 6.4 64-QAM ATDMA D3.0
6 35 41.4 6.4 64-QAM ATDMA D3.0 & 2.0
5 28.4 34.8 6.4 64-QAM ATDMA D3.0 & 2.0
4 23.6 26.8 3.2 16-QAM TDMA D1.x
3 20.2 23.4 3.2 QPSK TDMA D1.0 DSG
2 13.6 20 6.4 64-QAM SCDMA D3.0
1 7 13.4 6.4 64-QAM SCDMA D3.0
TV IF
Euro Split
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 14
Total Power Was only one US ch, now up to 4 chs Txing at same time
– Possibly 6.4 MHz each; nearly 26 MHz US channel loading
Lots of power hitting US laser
Probability of laser clipping is increased, especially if using legacy Fabry-Perot (FP) lasers– Distributed Feedback (DFB) lasers have more dynamic range
Use US 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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 15
Noise above ~40 MHz (~65 MHz in a Euro-DOCSIS network) is most likely caused by laser clipping
Laser Clipping
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 16
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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 17
Laser Clipping Artifacts
• 1.5 MHz AM causing Laser Clipping
• Possibly getting in at power insertion port of node
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 18
US Load Balance & Isolation Example
Attempting to “share” one US port across two other US ports– Can cause isolation issues– Load balance issues (ambiguous grouping)– Low Tx CM in HE/field can overcome isolation and show up on wrong ports
Exacerbated with wide-open power adjust continue window Note: D3.0 CMs in mtc-mode do not load balance on US
4-Way
4-WayCMTS US0@ 24 MHz
CMTS US1@ 24 MHz
CMTS US2@ 31 MHz
Fiber OpticRx 1
Fiber OpticRx 2
Filter
Amplifier
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 19
System Levels Reverse
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
• Less noise from low value taps
• Reduces potential “bleed-over”/ isolation issues
• Note: pad creates grp delay at cutoff , whereas EQ does not
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 20
Transmit Level Possibilities Running D3.0 CM in low mod scheme allows higher power
Use D3.0 CM in 2.0 mode– Single frequency on D3.0 CM offers 3 dB higher power
Minimum level of 20 dBmV could cause issues in lab or HE test CM– Pmin = +20 dBmV, 2560 ksym/s
– Pmin = +23 dBmV, 5120 ksym/s
Sample ATDMA Mod Profile
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 21
US Summary 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
Leverage D3.0 bonding for D2.0 tiers & services – Better stat-mux efficiency
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
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 22
Reasons CM Does Not Bond on Intended USs
CM not in w-online mode or maybe using 1.0 cm file
Mtc-mode off
Mtc-mode required-attribute & no attribute in cm file
No BG configured or incorrect fiber node config
CM not set for bonding or firmware issue
All US chs not “sta”– US(s) shut
– Max or Min Tx issues
– Poor MER, plant issues, mis-wired
Oversubscribed CIR– Call signaling (nRTPS), min US guaranteed speed,
– Could have multiple single ch bonding groups
Note: US service flows like UGS & RTPS assigned to single ch bonding
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 23
Why it’s Needed– Competitive pressure, offering higher tiers of service, more customers
signing up
Frequency Stacking Levels & Placement– What is the e-qam max output with four channels stacked
– Do channels have to be contiguous?
Isolation Concerns– Applications w/ different service grps lead to overlaid networks
– Signals destined for one node could “bleed” over to another
DS Frequency Expansion to 1 GHz– Amplifier upgrades are occurring now. It’s best to make the truck roll
once, so think about diplex filters, spacing, taps, etc.
DS Questions & Potential Concerns
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 24
Impairments That Could Affect DOCSIS 3.0
Isolation
Off-air Ingress
Attenuation
Freq assignments– Spectrum allocation– Plant limits
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 25
Difficult Architecture for Narrowcast
DS 0
US 0US 1US 2US 3
LC1x4
CMTS
• Optical splits create large service group (SG) sizing• Small narrowcast area or big mxn domain for large SG?
Small narrowcast area = small targeted area, but costly node splits
Large SG = better stat muxing & sharing, but more spectrum needed
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 26
M-CMTS = 100 Mbps Service Tier
Bonding across 4
freqs & 4-ch load
balance for legacy CMs609
FN1 FN2 FN3 FN4 FN5 FN6 FN7 FN8
22
Frequency
ATDMA
B
TDMA
P
P
28
615
621
627
P
P
B
P
P
P
P
B
P
P
P
P
B
P
P
P
P
B
P
P
P
P
FN9 FN10
• 5, 4x4 MAC domains with ATDMA & TDMA USs• DS connector overlaid for 2 nodes
• 4 DS freqs
• 2 US freqs
16-QAM
64-QAM
3.2 MHz
6.4 MHz
PrimaryP
B Bonding
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 27
Frequency assignments– CMTS may be limited to 860 MHz or 1 GHz
– Legacy CMs (1.x & 2.0) limited to 860 MHz bandedge
– E-qam limited to contiguous 24 MHz or 4 channel slots
– CMs may be limited to 50 or 60 MHz passband
M-CMTS architecture requires DTI and local USs– Distance limitation, time offset differences, level differences
Resiliency is another topic to address– If one DS frequency goes bad in field, how do CMs recover or react?
E-qam licensing?
CM requires 1.1 config file
DOCSIS 3.0 DS Considerations
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 28
More DS = more US
Testing and maintaining multiple DS channels– Physical chs have not changed for DOCSIS 3.0
– Test equip with built-in CMs need to support bonding• May need to exclude from LB and other feature like pre-eq
DS ch bonding max power with 4 freqs stacked– Four chs stacked on 1 connector limited to 52 dBmV/ch
• DOCSIS 1.x/2.0 DS is 61 dBmV max output
DS isolation issues
DOCSIS 3.0 DS Considerations (cont)
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 29
M-CMTS, DS Overlay and Isolation Issues
DS Combiner
DSs 0-3 = 603 MHzOverlay = 609, 615 & 621 MHz
DS Tx
DS 0
DS 1
DS 2
DS 3
Edge-QAM
Potential Isolation Path
E-QAM with DTI DS Licensing? Contiguous QAMs? Level granularity?
Load balance between local & remote DSs could have timing issues
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 30
Isolation Amp
• Can this device handle 50 dBmV input with 4-8 ch loading?
W
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 31
D3.0 spec goes to 1 GHz, some equipment may not
D3.0 CM spec requires 60 MHz capture window
DPC3000 capture of 96 MHz over most spectrum– 82 MHz max window supported over entire spectrum
TI 4x4 CM (60 MHz window)
Brcm 8x4 CM (2, 32 MHz bands or 1, 96 MHz band)– DS freqs must be contiguous within tuner block unlike 4x4 CMs
– Can use RCC templates to setup both tuners
– New feature called Split Tuner creatse 2 Rx modules and moves tuners automatically without RCC templates
Put voice call service flows on a primary DS– cable docsis30-voice downstream req-attr-mask 0 forb-attr-mask 80000000
Design Rules & Restrictions
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 32
Targeted insertion of D3.0 – Leverage existing US chs while adding more DS capacity
– Load balance 1.x/2.0 and enable D3.0 when needed
Leverage D3.0 bonding for D2.0 tiers & services – Better stat-mux efficiency & improved consumer experience
Enable seamless upgrade to higher D3.0 tiers– Wire once & add QAM chs as tiers or service take-rates go up
Can also disable DS bonding– No cable mrc-mode
– Per-CM exclude with vendor specific MIB or TLV
DS Summary
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 33
What Does This Bandwidth Graph Represent?
Time
Mbps
38373635343332313029282726252423222120
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 34
10 Points to Ponder
1. Many speed sites report at layer 3 of OSI model– Configure cm file for 5-10% higher than marketed
2. No control over actual frame size (64-1518 B)– Frame size overhead 18/64 (28%) vs 18/1518 (1.2%)
– MTU affected by wireless, VPN, ….
3. Small frames = small DOCSIS pipes– Only 35 Mbps when all frames are DS VoIP of 229 B
4. PowerBoost™ can give perception of greater speed– Could cause issues when deciding to do node splits
– How to control peak rate
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 35
10 Points to Ponder (cont)5. DS TCP requires US acks
– US pipe could slow down DS speed tests
– Small US acks make US pipe worth less
• DOCSIS overhead usually 11 B per frame
• 10.24 Mbps raw = 9 Mbps usable, but only 7.5 with acks!
6. More frames = more PPS = higher CPU usage– At some point CPU in modem could (will) be bottleneck
– TCP (typically 2 DS per 1 US ack)
7. During congestion, you still want priority for VoIP signaling, maybe video acks, and CM registration
8. Load balancing is good, but what speed tier pushes customer to bonding?– Maybe >50% of linerate
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 36
10 Points to Ponder (cont)9. Netflix/Hulu TV are using ABR, which is TCP-based
– Will cause US traffic in form of acks
– New CMs may have ack suppression on by default
– Typical US to DS TCP ratio of ~2%
– With ack suppression, that can drop below 1%
Ack suppression doesn’t alleviate CM CPU
– DS IP video of 3-7 Mbps and may make ack suppression inefficient
– Implement PHS, but more testing needed
10.Many tweaks needed to get per-CM US speeds > 3 Mbps– Lots of concatenation leads to fragmentation
– Fragmentation adds headers
– Preamble & gaurdtime added to each fragment
– D3.0 US bonding can do concatenation and keep < 2000 B
May not require fragmentation, so less overhead
© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicUpstream 64-QAM 37