14.4.2.2.3 Mobility Management Entity VNF Components Mobility management entity (MME) is a key element in the control plane of the LTE mobility net- work. It supports subscriber and session management. Some of the functions that the MME provides include the following: Service Platforms Subscriber authentication by interacting with the Home Subscriber Server (HSS) Negotiation of security with the user endpoint (UE) Reachability of an idle UE Activation/deactivation of bearer sessions SAEGW selection for initial attach and inter-eNodeB handover Termination of Non-Access Stratum signaling Enforcement of roaming constraints Lawful intercept of signaling MME selection for handoffs with MME change The virtualized MME is designed to work with nonvirtualized MME instances also. 14.4.2.2.4 Home Subscriber Server VNF Components The Home Subscriber Server (HSS) is a master repository for a given user/subscriber, and contains data elements including user identification, user addressing, user profile information, authentication vectors, and user identity keys. Some of the functions that HSS provides are Functions to store and update the following types of information: User identification, numbering, and addressing information Security data, including user identity keys User registration and user profile Location information Generation of security keys for authentication, ciphering, etc. Support for session control and management by providing authentication In the virtualized implementation, the HSS is decomposed into HSS-FE (front-end) and HSS-BE (back-end) VNFs. The evolution of the HSS-BE is to use a cloud database that enables scalability and the ability to provide data where needed. 14.4.2.2.5 User Data Repository VNF Components The virtualization effort has enabled the opportunity to work toward 3GPP defined user data con- vergence (UDC). The goal of virtualization efforts is to build a user data repository (UDR) that provides all types of user/subscriber information to various network functions involved in providing mob