a UE to the EPC (for non-trusted non-3GPP access) by means of an IP Security (IPSec)* tunnel between itself and the UE. 3GPP Anchor manages mobility for 2G/3G and LTE systems. SAE Anchor manages mobility for non-3GPP radio access technologies. Serving GPRS Support Node (SGSN) provides connections for GSM EDGE Radio Access Network (GERAN) and UTRAN networks, and is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (i.e., attachment and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information and user profiles of all GPRS users registered with this SGSN. Policy and Charging Rule Function (PCRF) manages QoS aspects and encompasses the following functions for IP Connectivity Access Network: flow-based charging including charging control and online credit control and policy control (e.g., gating control, QoS control, QoS signaling, etc.) [32]. Home Subscriber Server (HSS) is a master user database that supports the IMS network entities and contains the subscriber profiles. It performs authentication and authorization of the user, and can provide information about the subscriber's location and IP information. It is similar to the GSM Home Location Register (HLR) and Authentication Center (AUC). Reference Points S1 provides access to E-UTRA radio resources for the transport of user-plane and control-plane traffic/signaling. The S1 reference point enables MME and UPE separation, and further allows deployments of combined MME and UPE components. S2a provides the user-plane related control and mobility support between a trusted on-3GPP IP access and the System Architecture Evolution (SAE) Anchor. S2b provides the user-plane related control and mobility support between ePDG and the SAE Anchor. S3 enables user and bearer information exchange for inter-3GPP access system mobility in idle and/ or active 