There's beginning to be some expectation that there will be a transmission capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may be looked at carefully as packet over Sonet solutions emerge.
I.e. a dual clearline DS-3 actually carries as much user data as OC-3c ATM. Which, incidentally, was why SprintLink backbone design is easily expandable to dual links (that includes carefully considering implications for routing). Sean presented that design on NANOG a year ago, BTW. Funny thing, the design is expandable beyond that, too, so OC-3 ATM is already obsolete.
--vadim
Other than the SprintLink design Vadim mentions above, what other alternatives are emerging for high bandwidth IP transport? Is anyone implementing PPP over SONET (RFC 1619)? Shikhar