state. It is based on Gn reference point as defined between Serving GPRS Support Nodes (SGSN). The General Packet Radio Service (GPRS) is a packet-switched mobile data service available to Global System for Mobile communications (GSM) users, as well as in the 3G systems. S4 provides the user-plane with related control and mobility support between GPRS Core and the 3GPP Anchor, and is based on Gn reference point as defined between SGSN and Gateway GPRS Support Node (GGSN). S5a provides the user-plane with related control and mobility support between MME/UPE and 3GPP anchor. *IP Security (IPsec) is a set of protocols for securing IP-based communications by authenticating and encrypting each IP packet of a data stream. IPSec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session. IPSec can be used to protect data flows between a pair of hosts, between a pair of security gateways, or between a security gateway and a host [3]. 2.8 Overview of 3GPP evolved packet core network architecture S5b provides the user-plane with related control and mobility support between 3GPP Anchor and SAE Anchor. S6 enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (i.e., AAA interface). S7 provides transfer of QoS policy and charging rules from Policy Charging Rule Function (PCRF) to Policy and Charging Enforcement Point (PCEP). SGi is the reference point between the EPC and the packet data network. Packet data network is an operator's external public/private network or an intra-operator packet data network for provision of IMS services. Iu and Gb are interfaces with UTRAN and GERAN, respectively. The E-UTRAN architecture is shown in Figure 2-9. The E-UTRAN comprises Evolved NodeB (eNB), or equivalently E-UTRA base stations, providing the E-UTRA user-plane and control-plane protocol terminations towards the user equipment. Note that the Radio Netw