Transcript Deploying Upstream ATDMAppt

HFC Plant
Optimization for D3.0
John J. Downey
Consulting Network Engineer
Cisco Systems
Upstream 64-QAM
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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
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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
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Pre-EQ
Upstream 6.4 MHz bandwidth 64-QAM signal
Before Adaptive EQ:
Substantial in-channel tilt caused correctable
FEC errors to increment. CMTS’s reported
US MER (SNR) was 23 dB.
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.
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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 drilldown 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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6
CBT Display
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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 /
MicroReflections
Ok
Bad
Bad
Eventually Bad
• Ingress cancellation will cancel some CPD
• CPD resembles AWGN when all DSs are digital
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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
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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”
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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 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
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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 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
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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
Upstream 64-QAM
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Sample Upstream Spectrum Usage
Euro
Split
Upstream 64-QAM
#
From
To
BW
Modulation
Style
Primary
Usage
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
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TV IF
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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
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Laser Clipping
 Noise above ~40 MHz (~65 MHz in a Euro-DOCSIS
network) is most likely caused by 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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Laser Clipping Artifacts
• 1.5 MHz AM causing Laser
Clipping
• Possibly getting in at power
insertion port of node
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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)
– 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
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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
23
500’
2
17
FEQ
w/ US
pad
600’
2.5
Input 17
Reverse 43 dBmV
transmit
level @ the tap
42
39.5
PIII .5” cable
.40 dB @ 30 MHz
A total design variation of ~14 dB!
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Step
Attenuator
or EQ tap
29
X 38
• Less noise from low value
taps
• Reduces potential “bleedover”/ isolation issues
• Note: pad creates grp
delay at cutoff , whereas
EQ does not
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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
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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
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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
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DS Questions & Potential Concerns
 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.
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Impairments That Could Affect DOCSIS 3.0
 Isolation
 Off-air Ingress
 Attenuation
 Freq assignments
– Spectrum allocation
– Plant limits
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Difficult Architecture for Narrowcast
CMTS
DS 0
US 0
LC US 1
1x4 US 2
US 3
• 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
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Upstream 64-QAM
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M-CMTS = 100 Mbps Service Tier
Frequency
• 4 DS freqs
• 2 US freqs
B
Bonding
P
Primary
627
P
P
P
P
P
621
615
P
B
P
P
B
P
P
B
P
P
B
P
P
B
P
609
P
P
P
P
P
Bonding
across 4
freqs & 4-ch
load
balance for
legacy CMs
16-QAM
64-QAM
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TDMA
22
ATDMA
3.2 MHz
6.4 MHz
FN1
FN2
FN3
FN4
FN5
FN6
FN7
FN8
FN9
FN10
• 5, 4x4 MAC domains with ATDMA & TDMA USs
• DS connector overlaid for 2 nodes
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DOCSIS 3.0 DS Considerations
 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
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DOCSIS 3.0 DS Considerations (cont)
 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
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M-CMTS, DS Overlay and Isolation Issues
DSs 0-3 = 603 MHz
Overlay = 609, 615 & 621 MHz
DS 0
Potential Isolation Path
DS Combiner
DS 1
DS Tx
 E-QAM with DTI
 DS Licensing?
 Contiguous QAMs?
 Level granularity?
DS 2
 Load balance between local & remote
DSs could have timing issues
DS 3
Edge-QAM
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Isolation Amp
W
• Can this device handle 50 dBmV input with 4-8 ch loading?
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Design Rules & Restrictions
 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
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DS Summary
 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
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What Does This Bandwidth Graph Represent?
Mbps
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
Time
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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
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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
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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
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