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I agree some reflector discussion would be helpful on this topic.
I characterize the discussion I heard around the choice of PMD as really boiling down to a debate on the primary applications and the drivers for those applications.
The original justification for adding the 40G SMF objective was primarily based on the application of Data Center inter-switch links. There was also other applications such as for use in interconnecting to OTN equipment which is good for BMP. In both cases lower cost solutions are preferential. The debate appears to revolve around what other assumptions there are around market timing, technology risks, cost projections and operational issues etc.
To me the simple view is that to achieve low cost, you need higher volume. Higher volume is achieved by the having a solution that addresses the largest primary application and as many others as possible. I am assuming that the primary application is still the DC.
Since DC applications are inherently much more sensitive to cost, a near term low cost solution is needed or else the application will likely not be adopted. In this case, if 40G SMF PMD is uneconomical in the near term then the DC users will likely stay with nx10G as long as possible and then presumably assess the 40G/100G economics at some later date.
The argument for adopting serial technology now is that the potential higher volume of the DC application will trigger the necessary development investments now and drive the cost of that technology down so we will ultimately get it to the low cost solutions needed. My concern is that the timing and cost windows needed for the DC application do no fit with that model and we would end up with little adoption in that market and end up with a lower volume, higher cost PMD which is what we would all like to avoid.