In order to achieve the requirements in previous section, the LTE radio access network E-UTRAN architecture is improved dynamically from 3G/3.5G radio access network UTRAN. It has been changed to be flat from legacy hierarchy mobile network architecture. The functions of eNB in E-UTRAN include not only base station (NodeB) to terminate radio interface but also Radio Network Controller (RNC) to manage radio resource.
“The evolved UTRAN consists of eNB, providing the evolved UTRAN U-plane and C-plane protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interfaces. It is assumed that there always exist an X2 interface between the eNBs that need to communicate with each other, e.g., for support of handover of UEs in LTE_ACTIVE. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core). The S1 interface supports a many-to-many relation between aGWs and eNBs.”