"Performance guarantees are stochastic rather than deterministic. The worst case performance (for metrics such as number of hops and oversubscription) is known, but for RNG our models are stochastic (i.e., the worst case performance is known with high probability). This is a weaker limitation than it might appear. Fat-tree guarantees are also effectively stochastic once you account for real-world failures, which are frequent at scale. RNG simply makes the stochastic nature explicit and designs for it from the start."