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© 2009 Cisco Systems, Inc. All rights reserved.Cisco ConfidentialPresentation_ID 1 DOCSIS 3.0 Upstream Channel Bonding in the “Real World” John Downey, Consulting Network Engineer – CMTS BU
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 2 Presentation_ID Agenda ATDMA Refresher Frequency Stacking –CM Upstream (US) max output –Channel placement Plant Effect –Power/Hz & laser clipping –US expansion to 85 MHz? Options to “KISS”
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 3 Presentation_ID Why Bother 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
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 4 Presentation_ID US Best Practices 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.
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 5 Presentation_ID 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.Cisco Confidential 6 Presentation_ID US MER(SNR) Issues Doubling ch width can drop MER > 5-8 dB! Equalized vs unequalized MER readings Modulation profile choices –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 Pre-EQ effect –Great feature in 1.1 & > CMs –Could mask issues
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 7 Presentation_ID D3.0 US Issues 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
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 8 Presentation_ID US Level Issues Max Tx for D 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.Cisco Confidential 9 Presentation_ID Total Power 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
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 10 Presentation_ID Laser Clipping Green line represents flat US noise floor with no clipping Blue trace indicates laser clipping Clipping distortion above diplex filter roll-off frequency
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 11 Presentation_ID US Frequency and Channel Placement Freq assignments; 5 to 42, 55, 65, 85 MHz? –Diplex filters, line EQs, step attenuators, equalized taps –CPE overload (TV IF between 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.Cisco Confidential 12 Presentation_ID Sample Upstream Spectrum Usage #FromToBWModulationStylePrimary Usage QAMATDMAD QAMATDMAD QAMATDMAD QAMATDMAD QAMATDMAD3.0 & QAMATDMAD3.0 & QAMTDMAD1.x QPSKTDMAD1.0 DSG QAMSCDMAD QAMSCDMAD3.0 TV IF Euro Split
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 13 Presentation_ID 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 –High loss tough to overcome US load balancing presents potential issue where an US laser could be transmitting same time as another US laser Combining 32 lasers feeding 1 Rx in HE is addressed with lasers timed with actual traffic from house Will S-CDMA pose same problems? This multiplexing scheme allows multiple CMs to transmit same instant in time
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 14 Presentation_ID Reasons CM Does Not Bond on Intended USs 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.Cisco Confidential 15 Presentation_ID 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 can overcome isolation and show up on wrong ports Note: D3.0 CMs in mtc mode do not load balance on US 4-Way CMTS 24 MHz CMTS 24 MHz CMTS 31 MHz Fiber Optic Rx 1 Fiber Optic Rx 2 Filter Amplifier
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 16 Presentation_ID System Levels Reverse ’ 500’600’ 1.5 dB Input 43 dBmV PIII.5” cable MHz Reverse transmit 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 38 X
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 17 Presentation_ID Transmit Level Possibilities 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”
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 18 Presentation_ID Summary 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
© 2009 Cisco Systems, Inc. All rights reserved.Cisco Confidential 19 Presentation_ID Per-CM Speeds Uses CCF, so minislot size not an issue Cable default-phy-burst 0 needed –CSCtc92186 is for tracking multiple outstanding request behavior for non bonded CM (non-mtc-mode) Corrected with TI release Bighorn adds mtc-mode, which adds 400 usec to map advance Default SID cluster config is good to ~50 Mbps –Increase # of clusters to 2 & # of requests to 4 This will give 100 Mbps on 4 x 64QAM
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