This memo proposes adding Explicit Congestion Notification (ECN) to the Internet Protocol (IP) to enhance congestion control and avoid unnecessary packet drops. The proposal is based on the current use of packet drops by TCP to indicate congestion and the introduction of active queue management (e.g., Random Early Detection, RED) to detect congestion before queue overflow. Routers could set a Congestion Experienced (CE) bit in the packet header instead of dropping packets, allowing transport protocols to react to congestion more efficiently. The proposal includes two new bits in the IP header: the ECN-Capable Transport (ECT) bit and the CE bit. The ECT bit indicates that the transport protocol is ECN-capable, while the CE bit indicates congestion. TCP requires additional mechanisms, such as negotiation during setup and new flags in the TCP header, to support ECN. The proposal also addresses issues related to non-compliant end nodes and network components, ensuring that ECN does not compromise the integrity of the network. The memo discusses the benefits of ECN, including reduced packet drops and retransmit timeouts, and provides a detailed implementation plan for TCP and IP.This memo proposes adding Explicit Congestion Notification (ECN) to the Internet Protocol (IP) to enhance congestion control and avoid unnecessary packet drops. The proposal is based on the current use of packet drops by TCP to indicate congestion and the introduction of active queue management (e.g., Random Early Detection, RED) to detect congestion before queue overflow. Routers could set a Congestion Experienced (CE) bit in the packet header instead of dropping packets, allowing transport protocols to react to congestion more efficiently. The proposal includes two new bits in the IP header: the ECN-Capable Transport (ECT) bit and the CE bit. The ECT bit indicates that the transport protocol is ECN-capable, while the CE bit indicates congestion. TCP requires additional mechanisms, such as negotiation during setup and new flags in the TCP header, to support ECN. The proposal also addresses issues related to non-compliant end nodes and network components, ensuring that ECN does not compromise the integrity of the network. The memo discusses the benefits of ECN, including reduced packet drops and retransmit timeouts, and provides a detailed implementation plan for TCP and IP.