* We can run the world-wide telephone system say by IPv6 * * > > over SDH?

you can run CBR services over Guaranteed Service - however to get the jittler low enough over low speed links (c.f. Parekh's thesis, or papers on the multi-node packet Generalized Processor Sharing analysis) the admission test fails for utilisations that are unacceptably low However, the IPv6 _backbone_ could VERY easily accomodate all the worlds phone traffic in a few years time......the aggregated phone reservations (i.e. trunk routed equivalent of ATM VPs, but IPv6 aggregatred flows) would work with high utilisation, sicne the number of switch/router hops, and the line speeds are so high.... also, if all end systems become PC+mike+adaptive audio tool, you can use the Controlled Load service, instread of the Guaranteed Service, and get VERY high utuilisation (also with adaptive compression, you only need 30% utilisation anyhow;-) so, yes, Christian is right....its in the math:-) jon