that is the problem with oversubscribing though. making it possible to say "you have a guaranteed bandwith of X% of the total capacity" is a hard problem to sol

that is the problem with oversubscribing though. making it possible to say "you have a guaranteed bandwith of X% of the total capacity" is a hard problem to solve, especially inside the core layers of the network, where traffic gets aggregated. How are you going to make sure every tenant gets its share of bandwith equally? It requires traffic engineering (like RSVP-TE, which in term requires an MPLS network.) and a proper QoS setup. both of which are not trivial to implement at scale. Going further down the network towards to aggregate layer is far more doable (between switches etc), but doing it across core links it is actually quite difficult to guarantee bandwith.