In this illustration we see Host A and Host B side-by-side, with A on the left and B on the right. Each host appears next to its protocol stack. Between and below them is a cloud representing the network; inside the network is a series of five routers. Each router has two blue arrows passing through it, representing pathways of data.

Host A is sending data to Host B. This data originates in the top layer of Host A's protocol stack; it travels down through the stack and into one of the routers in the network. The data passes through the first router and into a second, through this router and into a third, and through this router and upwards into Host B's protocol stack. The data arrives in the top layer of Host B's protocol stack.

A gray arrow, representing a message of congestion information, extends from the second router to the second-to-top layer of Host A's protocol stack. This arrow is labeled "Direct network feedback." A second gray arrow extends from the second-to-top layer in Host B's protocol stack to the same point in Host A's protocol stack. This arrow is labeled "Network feedback via receiver."