John Downey, Consulting Network Engineer – CMTS BU
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
1

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–CM Upstream (US) max output
–Channel placement

–Power/Hz & laser clipping
–US expansion to 85 MHz?

Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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 Need more speed to retain customers
 Faster US speed needed for faster DS TCP speed
 Allow more chs for 1.x & 2.0 CMs to load balance
 Limit or reduce node splits
 Introduce new US service of 50 to 100 Mbps
 Allow migration of existing customers to higher tier and DOCSIS 3.0 capabilities
 Better Stat Muxing of medium tiers
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Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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 Assuming one or more ATDMA chs and one TDMA ch
– Provide quarantine ch of TDMA for 1.x CMs and/or settop boxes
– Load balancing 2.0 CMs to TDMA ch complicates things
• Explained later and may require DOCSIS restricted LBGs
 Keep US freqs relatively close & same phy parameters when freq stacking
 Bond US channels of similar parameters/speed
 Use caution with rate adapt – refer to rate adapt paper
 Logical channel 1 intended for lower/more robust modulation
 Best to use 6.4 MHz if possible instead of 2, 3.2 MHz wide channels
 Recommended not to bother with odd constellations like 8 or 32-QAM
– MER requirements not much different than those for next higher mod
 Spectrum allocation has many variables such as; group delay, known ingress freqs, etc.
4
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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ATDMA General Deployment Recommendations
 After increasing CW to 6.4 MHz, measure & document unequalized MER near CMTS US port
– Transmit at multiple test points in plant
 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 below 30 MHz
– Away from diplex filter grp delay
 Turn on Pre-Equalization
 Get rid of D1.x CMs or create “quarantine ch”
© 2009 Cisco Systems, Inc. All rights reserved.
Presentation_ID Cisco Confidential
5

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–64-qam for data
–16-qam for maintenance & VoIP?
–Max output for 64-QAM is 54 dBmV
• “cab up n power-adjust continue x” can help

–Great feature in 1.1 & > CMs
–Could mask issues
© 2009 Cisco Systems, Inc. All rights reserved.
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 Frequency Stacking
– What freqs to use, level considerations, laser clipping?
 Diplex Filter expansion to 85 MHz
– If 1GHz amp upgrades planned, think about pluggable diplex filters
– Potential CPE overload
– RFoG could be perfect scenario (maybe even 200 MHz)
 How graceful is resiliency (partial mode)
 Monitoring, Testing, & Troubleshooting
– Test equipment may need to have D3.0 capabilities
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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 Max Tx for D2.0 64-QAM for 1 ch is 54 dBmV
 D3.0 spec raised US ch max power by 3 dB
– Max of 57 dBmV for 32 & 64-QAM
– Max of 58 dBmV for 8 & 16-QAM
– Max of 61 dBmV for QPSK
 Max output is limited when stacking & drops 3 dB every time you double
– If not maxed out, levels don’t change
– Four freqs stacked at 64-QAM maxes out at 51 dBmV/ch
 CM ranging is different for 3.0 vs legacy
– CM will have some dynamic range to allow specific chs to be a few dB different vs. other chs
© 2009 Cisco Systems, Inc. All rights reserved.
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 One US ch now could be 4 chs Txing at same time
– Possibly 6.4 MHz each; nearly 26 MHz US ch loading
 Lots of power hitting US laser Tx
 Probability of laser clipping increases, especially if using legacy FP lasers
– DFB lasers have significantly more dynamic range
– BDR (baseband digital return) is another option
 Monitor systems above 42 MHz to see 2 nd & 3 rd order harmonics
– Any burst noise above diplex filter coming out of US receiver is usually indicative of laser clipping
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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9

Clipping distortion above diplex filter roll-off frequency
 Green line represents flat US noise floor with no clipping
 Blue trace indicates laser clipping
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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 Freq assignments; 5 to 42, 55, 65, 85 MHz?
– Diplex filters, line EQs, step attenuators, equalized taps
– CPE overload (TV IF between 41-47 MHz)
– Placement of different ch types
 Each US ch used for bonding is an individual ch
– Don't have to be contiguous
– Can have different phy layer attributes like;
• Modulation, ch width, tdma or scdma, etc.
– But, may be wise to bond “like” channels
 May be wise to keep freqs relatively close so plant problems like loss and tilt don’t cause issues
© 2009 Cisco Systems, Inc. All rights reserved.
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11

Euro
Split
# From To BW Modulation Style
10 61.4
64.6
3.2
64-QAM
9 54.8
61.2
6.4
64-QAM
8 48.2
54.6
6.4
64-QAM
7 41.6
48 6.4
64-QAM
6 35 41.4
6.4
64-QAM
5 28.4
34.8
6.4
64-QAM
4 23.6
26.8
3.2
16-QAM
3 20.2
23.4
3.2
QPSK
2 13.6
20 6.4
64-QAM
1 7 13.4
6.4
64-QAM
ATDMA
ATDMA
ATDMA
ATDMA
ATDMA
ATDMA
TDMA
TDMA
SCDMA
SCDMA
Primary
Usage
D3.0
D3.0
D3.0
D3.0
D3.0 & 2.0
D3.0 & 2.0
D1.x
D1.0 DSG
D3.0
D3.0
TV IF
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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12

 CM not in w-online mode or 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 are assigned to single ch bonding
© 2009 Cisco Systems, Inc. All rights reserved.
Presentation_ID Cisco Confidential
14

CMTS US0
@ 24 MHz
4-Way
Fiber Optic
Rx 1
Filter
CMTS US2
@ 31 MHz
Amplifier
Fiber Optic
Rx 2
4-Way
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 can overcome isolation and show up on wrong ports
 Note : D3.0 CMs in mtc mode do not load balance on US
© 2009 Cisco Systems, Inc. All rights reserved.
Presentation_ID Cisco Confidential
15

CS(CEQ) tap
• 17 dB at 5 MHz & 32 dB at 1 GHz
• Eliminates max transmit CMs
• Eliminates high DS tilt to TV
26
350’
23
500’
17
FEQ w/ US
1.5 dB 2 2.5
Input 17
4
Step
Attenuator or EQ tap
Reverse
43 dBmV transmit level @ the tap
42 39.5
PIII .5” cable
.40 dB @ 30 MHz
Presentation_ID
A total design variation of ~14 dB!
© 2009 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
38
16

 Use D3.0 CM in 2.0 mode
– Single frequency on D3.0 CM offers 3 dB higher power
 Running D3.0 CM in low mod scheme allows higher Tx power
 SCDMA with more codes may allow higher Tx power depending on implementation
 Min level could cause issues in lab or HE test CM
– Pmin = +17 dBmV for 1.6 MHz
– Pmin = +20 dBmV for 3.2 MHz
– Pmin = +23 dBmV for 6.4 MHz
– Note : This is much worse with SCDMA plus, CMs with low Tx have huge range for potential laser clipping or “bleed-over”
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
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17

 Long term D3.0 service planning
– Ensure optimized frequency allocation
– Enable seamless upgrade to higher D3.0 tiers
– Wire once
 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
18
Presentation_ID © 2009 Cisco Systems, Inc. All rights reserved.
Cisco Confidential