congestion control
termnetworking
The sender's job of inferring how much the network can carry and slowing down before it collapses - distinct from flow control, which protects the receiver.
It exists because the network gives no explicit signal: a sender learns about congestion from its own losses and delays, and reacts. That inference is why a single busy link changes behaviour end to end, and why measuring a network from one endpoint tells you as much about the path as about the host. The classic failure was congestion collapse in the 1980s, when every sender answered loss by retransmitting harder; the modern one is bufferbloat, where oversized buffers hide the loss and the sender never learns to slow down.
Also known as: congestion avoidance, slow start