The life cycles of transceivers at each speed node are exceedingly long, extending 6 – 10 years or more, with multiple generations in each node.

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I have a technical question that springs from this statement. In what way can transceivers of different speeds be mixed together? If you have a data center that was originally outfitted uniformly with 100g transceivers, and a certain percentage of those fail during a time when faster replacements are available, can you mix in 200g and 400g units to replace the failed 100g units? 

If so, how is it done? does a single blade NEED all attached transceivers to be uniform in speed? is the speed of the faster units totally moot when mixing with slower ones on the same blade, or will any faster one(s) provide an overall speed increase?

Put more simply, does the entire data center need to be retrofitted if any speed increase is to take place?