GGSN network element provides the network gateway function for MS to access the network. It is responsible for packets encapsulation/de-encapsulation, forwarding between 2/3G network and PDN network. SGW network elements is network serving gateway, and responsible for user plane packets forwarding. It is also responsible for SAE session and bearer context management and store, terminating the downlink packets for the UE in idle status. In addition, it is the mobile access anchor of 3GPP access. PGW is packets data gateway, it is responsible for UE IP address management, and it is a mobile anchor between 3GPP access and non-3GPP access. The ePDG is responsible for setting up connection between WLAN network and EPC network. It makes the UE can enjoy the service provided by EPC network by WLAN. The ePDG is one of key network elements of VoWiFi solution.