What does 'ECN' stand for in the context of IPv4?

In the context of IPv4, 'ECN' stands for Explicit Congestion Notification. This is a network traffic management feature that allows a router to inform endpoints about network congestion without dropping packets. When a router experiences congestion, instead of dropping packets, it sets an ECN field in the IP header of packets. This informs the end devices that congestion is occurring and allows them to reduce their transmission rates before packet loss happens. This proactive approach helps maintain overall network performance and reduces the negative effects of congestion, promoting more efficient network communication.

The other options do not accurately reflect the term used in networking. Enhanced, Effective, and Extended Congestion Notification are not standard terminology relating to IPv4 or ECN, as the correct and widely recognized term is explicitly defined as Explicit Congestion Notification.