Yesterday, I went to a SCTE seminar by Jason Lowe, VP, at ClearCable Networks,  The seminar focused mostly on the technologies used by MSOs (cable TV companies), especially DOCSIS.  But he also talked about the distribution network technologies RFoG, G-PON and E-PON.  Today I am going to make some comments on DOCSIS.

He started off with a great overview of cable basics, and many of the network design issues including CNR (Carrier to Noise Ratio), CTB (Composite Triple Beat), QAM trade-offs, Fiber Loss, BER (Bit Error Rate) vs. MER (Modulation Error Rate).  He also spent a lot of time discussing real world operational problems, oxidized copper connections, bad connections, poor decisions made by techs, undocumented changes, etc.  I can’t possibly hit on all of the interesting points; I recommend that you try to catch one of his courses too.

He then moved on to DOCSIS.  The goal of DOCSIS was to provide a wide-range of through “always-on” internet.  Way back in 1997, when everyone was using dial-up internet, that really was a radical idea.

With well-defined standards, and a standards testing process, the cableco’s almost achieved the elusive goal of true vendor interoperability between CMTS, cable modems and other equipment.  With the huge success of MSOs in the internet area, it is clear that DOCSIS has fulfilled its goals.

The latest release will be DOCSIS 3.1.  Its goal is to provide higher speeds, comparable to G-PON of 2.5 Gbps downstream and 1 Gbps upstream.  This should be achieved through:

  • Higher order modulation of 4096 QAM
  • OFDM (Orthagonal Frequency Division Multiplexing) downstream and OFDMA (Orthogonal Division Multiple Access) Upstream to replace Single Channel QAM (SC-QAM)
  • Improved Forward Error Correction (FEC), moving from Reed –Solomon to Low Density Parity Check (LDPC)

For more details on the DOCSIS 3.1 specification, refer to

So let’s get to the exciting stuff.  Are there some conclusions?

  1. DOCSIS 3.1 appears to address many of its present short-comings, and may allow it to address the speed gap with G-PON.
  2. There are no DOCSIS 3.1 products available today. We are probably looking at 2016 GA for certified products.
  3. As current DOCSIS 3.0 CMTS will not be able to be upgraded to DOCSIS 3.1, this may be a good time to hold off on spending CapEx on CMTS.  A further obvious conclusion, as DOCSIS 3.1 will require replacing CMTS, it will be very expensive to deploy.
  4. As soon as DOCSIS 3.1 modems become available, start to buy and deploy them.  They will be backward compatible with DOCSIS 3.0 CMTS, so start to get them out into the field as soon as possible.

And now for a commentary by me.  If you must purchase a CMTS in the next 12-18 months, this is an excellent time to investigate the option of purchasing used or surplus units.  Contact us at to get a quote on your Cisco, Motorola (acquired by Arris) or Arris CMTS.

For more details on the  vendor hardware options, check out:


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