Prototyping Systems on Chip (SoC) on FPGA technology improves the time that the de- signer needs to spend in the verification stage when developing new systems or upgrading the existing ones. However, FPGA prototyping is very challenging due to the few resources available in this chips, and often the large designs do not fit into one single FPGA. Since Net- works on Chip (NoC) are used as SoC interconnects, extending them for offering communication services between two different chips will solve the problem. This work explores how a bridge can extend the NoC while providing Quality of Service (QoS) to the applications. After a detailed investigation of the NoC protocol stack, we found that the best layer for placing the bridge was at the transport layer. Here, the bridge multiplexes several NoC connections on an off-chip link, with data granularity of words. The bridge offers QoS by means of TDM scheduling and a credit-based mechanism preserves the end-to-end flow-control offered by the NoC. Software and hardware implementations of this bridge are tested and verified showing that they are fully func- tional. Moreover, two different NoC configuration procedures are developed, so the SoC resources can be monitored from an external host. Finally, this work concludes that it is possible to extend a NoC over more than one single chip without loosing the QoS and hiding the complexity of the off-chip link to the applications.