We present a novel methodology for design space exploration using a two-steps scheme to optimize the number of virtual channel buffers (buffers take the premier share of the router in a NoC [10]) used to implement logical channels multiplexed across the physical channel in a router output port for QoS supported on-chip communication. In the first step, the number of virtual channels is minimized during the mapping of tasks to the NoC at the design time of a System on Chip (SoC) for which we use a swarm intelligence-based Ant Colony Optimization (ACO) algorithm. In the second step, a probabilistic approach based on the traffic model of the application is used to further minimize the number of virtual channels. We achieve on average 90.2% reduction in the number of virtual channels compared to a fixed stateof-the-art (i.e. QNoC [1]) allocation for the E3S embedded application benchmark suit. The reduction depends on the designer and the QoS parameter, and it is dependent on the speci...