3GPP Release 8 Flat Network Architecture

3GPP R8 Evolved Packet System introduces flat network architecture where
the evolved NodeB (eNodeB) connects directly with the core network nodes.
The Mobility Management Entity (MME) assumes the role of the current
2G/3G SGSN and inherits more mobility management functionality from the
Radio Network Controller that merges with the eNodeB. Flat radio network
architecture deployed in 3GPP Release 8 strengthens the MME’s role as a
mobility management engine. It acts as a pure control element, taking care
of the following key tasks:
• Subscriber authentication and authorization
• Control plane traffic handling and security functions
• Session and mobility management within the LTE radio network and
between 2G/3G or CDMA and LTE radio networks
The GGSN equivalent in EPS is Serving Gateway and PDN Gateway (S/PGW).
The S/P-GW acts as a user plane gateway towards operator services
and the Internet. It interfaces with policing and charging control systems and
with 3GPP and non-3GPP radio networks.