FPGA prototyping of recent large Systems on Chip (SoCs) is very challenging due to the resource limitation of a single FPGA. Moreover, having external access to SoCs for verification and debug purposes is essential. In this paper, we suggest to partition a network-on-chip (NoC) based system into smaller sub-systems each with their own NoC, and each of which is implemented on a separate FPGA board. Multiple SoC ASICs can be bridged in the same way. The scheme that interconnects the sub-systems should offer the application connections the required quality of service (QoS). In this paper, we investigate bridging schemes at different levels of the NoC protocol stack. Comparing the distinct design criteria for the proposed schemes, a bridge is designed. The bridge experiments show that it provides QoS in terms of bandwith and latency.