A new massively parallel algorithm is presented for simulating large asymmetric circuit-switched networks, controlled by a randomized-routing policy that includes trunk-reservation. A single instruction multiple data (SIMD) implementation is described, and corresponding experiments on a 16384 processor MasPar parallel computer are reported. A multiple instruction multiple data (MIMD) implementation is also described, and corresponding experiments on an Intel IPSC/860 parallel computer, using 16 processors, are reported. By exploiting parallelism, our algorithm increases the possible execution rate of such complex simulations by as much as an order of magnitude. Gaujal, Bruno and Greenberg, Albert G. and Nicol, David M. Unspecified Center NAS1-18605; NAS1-19480; NSF ASC-88-19373; NSF CCR-92-01195; NAG1-1060; NAG1-995; RTOP 505-90-52-01...