We present smartacking, a technique that improves performance of Transmission Control Protocol (TCP) via adaptive generation of acknowledgments (ACKs) at the receiver. When the bottleneck link is underutilized, the receiver transmits an ACK for each delivered data segment and thereby allows the connection to acquire
the available capacity promptly. When the bottleneck link is at its capacity, the smartacking receiver sends ACKs with a lower frequency reducing the control traffic overhead and slowing down the congestion window growth to utilize the network capacity more effectively. To promote quick deployment of the technique, our primary implementation of smartacking modifies only the receiver. This implementation estimates the sender's congestion window using a novel algorithm of independent interest. We also consider different implementations of smartacking where the receiver relies on explicit assistance from the sender or network. Experiments in a wide variety of settings show beneficial impacts of smartacking on TCP performance, especially in environments with low levels of connection multiplexing on bottleneck links.