Systems and methods of optimizing packet flow in a network are disclosed. An internetwork includes plural networks, each network having plural non-router nodes and at least one router node. The non-router node of a first network can be configured to perform congestion control. The non-router node sends a request packet to a node in a second network. The value of a packet-in-flight counter associated with the network is adjusted when the request packet is sent to the second network node and when a response packet is received from the second network node. The non-router node determines whether another request packet can be sent to another network in the internetwork based on a value of the packet-in-flight counter.