I don't have a reference on hand to cite, but I recall more than one bit of reportage of studies of traffic analysis of this sort; the upshot was that researche

I don't have a reference on hand to cite, but I recall more than one bit of reportage of studies of traffic analysis of this sort; the upshot was that researchers found in practice that it revealed a surprising amount about the network and nodes being studied -- more than they'd anticipated. Encrypted content provides you no protection against this sort of analysis.