A Diameter edge agent (DEA) is a network component in a telecommunications network that performs routing functions and acts as an interface between the core Diameter network and external networks. It acts as a relay between Diameter clients and servers and provides security, reliability, and quality of service (QoS) for Diameter signaling messages. DEA is used in IP Multimedia Subsystem (IMS) networks, 4G/LTE networks, and other data networks that use the Diameter protocol to control and manage communication sessions. It helps to reduce the load on the core network and improve the scalability and performance of the overall system.