Summary
1. Of course, there will be a certain amount of moving from a 10G installed base to 40G capability. 2. However, from there, a 100G overlay on a different pair of fibers is likely to be the next step. 3. That would be more probable than putting all three rates on the same network today.
Analysis
Obviously, going from 10G to 40G to 100G on the same network can be done in principle. But one starts to lose some of the advantages that 100G provides with PM-QPSK (the modulation scheme of choice for that speed) in managing services coherently on one pair of fibers. The 10G OOK channels have a lot of cross-phase modulation impact on PM-QPSK. So, that is the limiting factor in being able to deploy homogeneous 10/40/100G networks. There is going to be a loss of some performance, which means higher cost.
On a different matter, the industry is still waiting for the two main standards – OIF and IEEE to finish their work so that specs can be delivered on 100G – and get away from a bunch of proprietary solutions from several vendors. At OIF, it can be amazing how many options are brought up on issues such as FEC, modulation technique, differential vs. non-differential encoding, etc. And the discussions tend to be all over the map. There is a natural unwillingness by the suppliers not to talk about the details of their own implementations. This kind of openness is necessary in order to make a value judgment on inferior or competitive solutions regarding performance compared to what is out in the industry.
