How does the 4G LTE architecture differ from 3G UMTS, and what are the key new components?

4G LTE replaced the split CS/PS core with a unified all-IP Evolved Packet Core (EPC), simplified the radio access to a flat architecture (eNodeB, no RNC), and introduced new core nodes: MME, S-GW, P-GW, and HSS.

* Flat LTE architecture: eNodeB plus the EPC nodes (MME, S-GW, P-GW, HSS). — Public domain, via Wikimedia Commons. *

3G vs 4G architecture comparison:

4G LTE core components:

• MME (Mobility Management Entity) — handles signaling: authentication, session management, mobility (but NOT user data)
• HSS (Home Subscriber Server) — like HLR+VLR combined — subscriber database
• S-GW (Serving Gateway) — local anchor for user data, handles handover between eNodeBs
• P-GW (Packet Data Network Gateway) — connects to the internet, assigns IP addresses (like GGSN)

Key architectural shift: In 4G, the control plane (signaling via MME) is separated from the user plane (data via S-GW/P-GW). This is a critical design principle that 5G takes even further.

Go deeper:

• EUTRAN + EPC main components (ShareTechnote) — a concise role-by-role breakdown of eNodeB, MME, S-GW, P-GW and HSS, splitting cleanly into "radio access vs core" so each box's job is unambiguous.
• System Architecture Evolution / EPC (Wikipedia) — best on the why: the flat all-IP design and the explicit control-plane / user-plane separation (incl. the later Sx/PFCP CUPS split that 5G inherits).
• Evolved Packet Core (Wikipedia) — kept for the carousel diagrams of the EPC node-and-interface layout (MME, S-GW, P-GW, HSS).