VoLTE is a voice communication service over IP Multimedia Subsystem (IMS) network, and its traffic is routed through Long Term Evolution (LTE) wireless network, Evolved Packet Core (EPC) core network and IMS core network. VoLTE adopts a full IP network framework based on Session Initiation Protocol (SIP), which makes VoLTE more vulnerable to attacks than traditional voice service which is based on circuit switch. Therefore, there is an urgent desire to establish the overall security framework for VoLTE network operation. Recommendation ITU-T X.1041 analyses security threats encountered by the VoLTE network and recommends countermeasures for telecommunication operators to ensure the secure operation. It also provides a security reference framework for VoLTE network.