6.1.4 Congestion on the ACK-path

6.1.4 Congestion on the ACK-path

For the current generation of TCP congestion control algorithms, pure acknowledgement packets (e.g., packets that do not contain any accompanying data) MUST be sent with the not-ECT codepoint. Current TCP receivers do not have a mechanism for reducing traffic on the ACK-path in response to a congestion notification. Mechanisms for responding to congestion on the ACK-path are areas for current and future research. (One simple possibility would be for the sender to reduce its congestion window when it receives a pure ACK packet with the CE codepoint set). For current TCP implementations, a single lost ACK typically has only very minor effect on the sending rate of the TCP.