Ericsson Ericsson It has been broadly demonstrated that user experience improvements for time-critical applications have not increased at the same pace as network throughput (i.e., the increased bandwidth does not result in a corresponding increase in the user experience). Optimizing network latency rather than throughput can lead to a significantly improved user experience for time-critical applications. Low Latency, Low Loss, and Scalable Throughput (L4S) technology, introduced in RFC 9330, uses Explicit Congestion Notification (ECN) bits by marking packets suffering potential congestion in the network. L4S operates as a congestion-control mechanism, using markers within the data packets to detect and promptly respond to congestion conditions. This feedback loop enables devices (e.g., endpoints such as client devices and server devices) to adjust data flow in real-time, preventing bottlenecks and ensuring smoother transmission. RFC 5129 describes a mechanism for supporting ECN in the Multiprotocol Label Switching (MPLS) data plane. That mechanism is based on the codepoints that take part in the Traffic Class (TC) field and, thus, prevent the use of TC field for traffic differentiation. This document defines how ECN can be supported in the MPLS data plane using the MPLS Network Actions technology.