The invention is a transaction interface protocol wherein the interface protocol has a transaction identifier signal in each of the request and response channels. It is used between a target network interface unit (NIU) master and an initiator NIU slave that are directly connected through a transaction interface. The target NIU response channel uses the transaction ID signal to identify the entry in a context array associated with the corresponding request. The coupling of target NIU and initiator NIU enable the formation of an on-chip interconnect comprising multiple network-on-chip (NoCs) wherein the topology of the interconnect is simpler, smaller, faster, and has lower latency.