ehavior of the network. The veri- fication leverages the structure of our NF abstract model, namely due to the use of state machine, for each flow the NF will be in one and only one state at any given time. Essentially, only one node in an NF's state will be active. By activating different nodes (corresponding to different states of an NF) during the verification process, we are able to verify different forwarding scenarios across NFs and states. 5.3 Core Network Functions Virtualization: The 3G packet core (PC) network consist of three interacting domains: core network (CN), 3G PC terrestrial radio access network (UTRAN), and UE. The main function of the core network is to provide switching, routing, and transit for user traffic. Core network also contains the databases and network management functions. It is the common packet core network for GSM/GPRS, WCDMA/HSPA, and non-3GPP mobile networks. The packet core system is used for transmitting IP packets. The core network is divided into circuit- and packet-switched domains. Some of the circuit-switched elements are mobile switching center (MSC), visitor location register (VLR), and gateway MSC. Packet-switched elements are SGSN and GGSN. Some network ele- ments such as EIR, HLR, VLR, and AUC are shared by both domains. The architecture of the core network may change when new services and features are introduced. Number portability database (NPDB) will be used to enable user to change the network while keeping their 5 SDN and NFV in 5G old phone number. Gateway location register (GLR) may be used to optimize the subscriber handling between network boundaries. The primary functions of the packet core with respect to mobile wireless networking are mobility management and QoS. These functions are not typically provided in a fixed broadband network, but they are crucial for wireless networks. Mobility management is necessary to ensure packet network connectivity when a wireless terminal moves from one base station to another. QoS is necessary because, unlike fixed net