“…In these cases, traditional methods cannot be readily extended. To overcome the difficulty, the weak convergence method was initially established by authors, such as W. Dai [1,2] , J. G. Dai and W. Dai [3] , for finite buffer networks, then along the similar line by authors like Williams [7,8,16] and Bramson [5,6] for certain family of multiclass networks. By the method, the keys to prove a heavy traffic limit theorem for multiclass networks with feedback are to show a state space collapse property and a completely-S property for some reflection matrix.…”