The LTE/EPC architecture is driven by the goal to optimize the system for packet data transfer.

Remember that There are no circuit switched components in LTE/EPC.
There is a new approach in the inter-connection between radio access network and core network. The EPS architecture is made up of an EPC (Packet Core Network, also referred as EPC) and an eUTRAN LTE Radio Access Network (also referred as LTE)
The CN provides access to external packet IP networks and performs a number of CN related functions (e.g. QoS, security, mobility and terminal context management) for idle (camped) and active terminals. The RAN performs all radio interface related functions.

The LTE/EPC radio access network – Evolved UTRAN (E-UTRAN) – will only contain Node Bs. No RNC is provided anymore. This means, that the evolved Node Bs take over the radio management functionality.

This will make radio management faster and the network architecture simpler. EUTRAN exclusively uses IP as transport layer. Behind the EPC follow one or more IP networks. A major example will be IMS, that can benefit especially from the QoS awareness of LTE.