Before revision:  We then  propose a variant of spatial branch and bound algorithm (V-SBB), that can achieve e-global  optimal solution to the original MINLP. We show numerically that V-SBB is more stable and robust than other candidate MINLP solvers under different network scenarios. More importantly, we observe that the energy efficiency under { our C3 optimization framework improves by as much as 88 \% compared to any C2 optimization between communication and computation or caching.
After revision:  We then propose a variant of spatial branch and bound algorithm (V-SBB), that can achieve e-global optimal solution to our problem { our C3 optimization framework improves by as much as 88 \% compared to any C2 optimization between communication and computation or caching.