We present DNOC, a network-on-chip simulator. DNOC simulates custom network topologies with detailed router models. Both classic virtual channel (VC) based router models and deflection routing models are supported. We validate the simulation models against hardware RTL router models. DNOC can generate various statistics, such as network latency and power. We evaluate the simulator in three typical use cases. In stand-alone simulation, synthetic traffic generators are used to offer load to the network. In synchronous co-simulation, the simulator is integrated as a module within a larger system simulator with synchronization every simulated cycle. In the faster model based co-simulation mode, a latency model is built, and re-tuned periodically at longer time intervals. We demonstrate co-simulation by running applications from the Rodinia and SPLASH-2 benchmark sets on mesh variants. DNOC is also able to run on multiple x86 cores in parallel, speeding up the simulation of large networks.