Heavy traffic analysis of open processing networks with complete   resource pooling: asymptotic optimality of discrete review policies
  We consider a class of open stochastic processing networks, with feedback routing and overlapping server capabilities, in heavy traffic. The networks we consider satisfy the so-called complete resource pooling condition and therefore have one-dimensional approximating Brownian control problems.   We propose a simple discrete review policy for controlling such networks.   Assuming 2+\epsilon moments on the interarrival times and processing times, we provide a conceptually simple proof of asymptotic optimality of the proposed policy. 
Baris Ata and Sunil Kumar