OFDMA Troubleshooting

OFDMA Upstream Troubleshooting. Tips, suggestions and recommendations. Another power hour of cable with Brady Volpe and John Downey CMTS Technical Leader at Cisco. More and more operators are introducing OFDMA into their networks and experiencing a learning curve with its introduction. Find out ways to overcome these issues and ask any questions you may have.

The discussion is on all things DOCSIS.

OFDMA “UPSTREAM” Troubleshooting:

• General intro
• OFMDA Upstream. The A means upstream
• 50% increase in upstream traffic
• Noise in return
• Cable Modems locking up
• CM locking up with OFDMA upstream
• Ingress etc
• Spectrum Analyzer can catch it if you use peak hold
• OFDMA with LDPC
• Get better speeds
• You pay a license for the channel
• OFDMA at low frequency
• Tickets will come in that subscribers cannot get traffic over these cable modems
• Lots of uncorrectable FEC
• CMTS says the cable modem is online but the subscriber says no not working
• So be proactive (PNM) and do not just rely on show cable modem in the CMTS
• Ping DOCSIS is done at CMTS – layer 3
• Station Maintenance Ping
• Check your MER first
• Layer three hung
• I cannot talk to Cable Modem remotely – You have to ask the customer to power cycle
• DOCSIS 3.1 Cable Modem do not have a catch all?
• When Cable modems run OFDMA – RXMER – Noise – profile from modem changes?
• Many variables impacting OFDMA
• Should you try to do ODFMA in the low end
• Stay away from noise when using OFDMA – use above 42MHz
• ATDMA – Increased power levels – power boost
• You don’t need to migrate all users to DOCSIS 3.1 modems to take advantage of OFDMA in the upstream
• Efficiency in both upstream and downstream
• Spectrum allocation recommendations
• Lot’s of feedback and comments from the chat
• You can have different variations for the channels
• Recommended to do lab testing before you deploy cable modems form certain chip sets, firmware etc
• OFDMA higher in frequencies than SCQAM
• RFOG – real compatibility issues with OFDMA
  • OBI
  • ONT – it has a switching function in it for RFOG
  • Too little energy/ power to turn laser on
• There are difference between broadcom and intel chip sets
• Power cycling and partial mode
• Cyclic Prefix – difference on downstream
• Setting in CMTS
• Configuration of OFDMA channel
• DRW –
  • Ends at 85 MHz in DOCSIS 3
  • Difference in transmit levels
  • DRW – kept 12dB spec window for DOCSIS 3.1
  • Going to 204 MHz
  • Cable loss is not flat
  • What happens if you have a suck out with this 12 dB window
  • IR – initial ranging
  • 1/3
  • Understanding your spectrum
  • OFMDA has pre-EQ
  • Transmit power issues with DRW
• John Downey gets stumped
• Tuning the cyclic -prefix with AI / PMA
  • 4k QAM, 8K QAM etc
• Benefits to DOCSIS 3.1 Cable Modems
• Great show with lots of activity in the Chat

End Podcast

John thank you for your time today. This was a great episode.  Our next Episode 73 in March 19th The Road to DOCSIS 4.0 with Jeff Finkelstein of COX.

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