LTE NETWORK ARCHITECTURE OVERVIEW
LTE network is a PS-Only System, where E-UTRAN is limited to a single node (ENodeB, or eNB). The eNB handles all radio access and control functions.
In the core network (EPC), the UMTS equivalent SGSN has been split into MME (Mobility Management Entity), which handles control functions, and Serving SAE GW (eAG), which handles U plane traffic. There is one anchor MME and eAG per UE. MME and eAG may be collocated.
The UMTS GGSN equivalent is PDN SAE GW (P-GW), which may or may not be collocated with Serving SAE GW. The P-GW is the inter-system anchor point for each UE. It provides access to PDNs.