The EPC cleanly separates control and user plane processing across three principal node types. The Mobility Management Entity handles every control plane task including authentication, paging, bearer management, and mobility signaling. The Serving Gateway anchors user plane data during handovers between eNodeBs and forwards traffic toward the internet. The PDN Gateway sits at the border between the mobile network and external packet data networks, assigning IP addresses, enforcing policy rules, and performing lawful intercept. This separation became so effective that 5G pushed it even further with CUPS.