The SAE has a flat, all-IP architecture with separation of control plane and user plane traffic. The Lte protocols and procedures pdf is the key control-node for the LTE access-network. MME and it is also responsible for generation and allocation of temporary identities to UEs.
NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. 3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming UEs. For idle state UEs, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the UE.
It manages and stores UE contexts, e. IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception. The PDN Gateway provides connectivity from the UE to external packet data networks by being the point of exit and entry of traffic for the UE.
A UE may have simultaneous connectivity with more than one PGW for accessing multiple PDNs. The functions of the HSS include functionalities such as mobility management, call and session establishment support, user authentication and access authorization. The main function of the ePDG is to secure the data transmission with a UE connected to the EPC over an untrusted non-3GPP access. NAS protocols support the mobility of the UE and the session management procedures to establish and maintain IP connectivity between the UE and a PDN GW. They define the rules for a mapping between parameters during inter-system mobility with 3G networks or non-3GPP access networks. They also provide the NAS security by integrity protection and ciphering of NAS signaling messages.