A simple distributed strategy for sharing a congestible path is additive increase, multiplicative decrease (AIMD).

While feedback indicates available capacity, a sender increases its allowed in-flight data gradually. When congestion is detected, it reduces that allowance by a multiplicative factor.

If a congestion window is 20 segments, an illustrative AIMD rule might grow it toward 21, 22, 23 during successful operation, then cut it to about 11 after a congestion signal. The exact rules of real transports are more detailed, but the shape matters: probe cautiously upward and retreat substantially when the path appears overloaded.

Multiple flows following compatible rules tend to move toward efficient sharing instead of increasing without bound.

AIMD is therefore best understood as a feedback-control strategy for distributed resource sharing, not merely as one TCP implementation detail.