Craig Partridge writes:
Once UUNET was acquired by Worldcom, UUNET had access to Worldcom's network infrastructure, which was heavily ATM, and which UUNET had to share with the Worldcom's (very lucractive) voice traffic. In that context, there was a real cost to using bandwidth and UUNET had to use account for its usage.
I can authoritatively say that UUNET never ran its backbone on the Worldcom customer-facing ATM network. For one thing, it was no larger than the IP backbone to start with and was quickly outpaced by the IP backbone, which ran on its own ATM network.
Some other ISPs were/are in a different business model -- they owned their fiber runs, outright, and the question for them was whether to put run ATM over that fiber, and subdivide the bandwidth of a single waveband, or light two wavebands (one voice/one IP). I've seen the marginal cost analysis for that kind of decision, and it often favors two wavebands.
I never looked at it this way, but then direct access to the fiber at Worldcom was not really an option. It was only a question of what we terminated circuits on. At the time, there were no IP routers that could credibly terminate OC12, which lent a certain clarity to the decisionmaking.