## 1 Introduction  
In recent years, with the development of Internet of Things (IoT) technology, IoT devices have become the mainstream devices of network terminals. Meanwhile, due to the surge in the volume of mobile multimedia services, multimedia data have become one of the most important sources of data traffic in networks [1]. To deal with the large volume of multimedia data generated by the huge amount of IoT devices in an effective and efficient way, mobile edge computing technology is becoming increasingly popular, which deploys computing and storage edge nodes in large numbers in order to improve mobile application capacity and reduce the response time of devices as well as the wireless back-trip network bandwidth pressure. In mobile edge computing scenarios, most of the wireless or mobile networks are open physical systems that use radio frequency technology for network connectivity and transmission. Therefore, in addition to the security problems shared by wired networks, wireless networks have several unique security threats. The transmission of multimedia data in wireless networks has its inherent difficulties, such as channel quality time change, mobile terminal heterogeneity, and limited wireless resources [2]. The emergence of edge computing alleviates these problems in terms of resource utilization. However, the wireless and open nature of mobile multimedia networks makes multimedia data vulnerable to malicious attacks. An attacker can easily intercept a user's data or directly attack the network. As a result, security in mobile multimedia data transmission has received increased attention [3]. These threats manifest themselves in three areas [4], as shown in Figure 1, which are also the key concerns in the design of security mechanisms for wireless or mobile networks to support multimedia communications or other services. 1. Physical layer. This mainly includes the threat of environment security, equipment security, and the threat caused by the malicious damage of the attackers, such as: * Stealing a user's device: when a wireless card is lost or stolen, an illegal user can breach an access point; * Wireless interference: interference with the normal operation of the wireless channel by transmitting a large power-to-frequency signal. 2. Data link layer. This mainly includes spoofing based on MAC addresses, such as: * Eavesdropping and listening: electronically eavesdropping on computer communications flowing through wireless networks; * Spoofing attacks: redefining the MAC address of a wireless network or network card. 3. Network layer. This includes various attacks from the network, such as: * Inserting an attack: impersonating a legitimate user, accessing an information system through a wireless channel, and gaining control; * Denial of service: an attacker maliciously occupies almost all resources of the host or network, making them unavailable to legitimate users; * A network takeover: an attacker takes over a wireless network or session process, allowing all traffic to reach the attacker's machine; * Energy consumption: the destruction of energy-saving mechanisms, such as by constantly sending connection requests, preventing the device from entering the energy-saving mode. For wireless network security threats, mobile network servers are generally sufficient to support the setup of security measures. However, the power and processing capacity of sensor nodes located within the edge networks are typically low, leaving a small power budget for security measures. A large number of low-cost, energy-limited nodes deployed in uncontrollable areas and a complex, harsh application environment can lead to a variety of failures that reduce or eliminate monitoring functions, causing economic  
Figure 1: Security threats of mobile network. loss to users, and even network paralysis [5]. Therefore, detection of abnormal nodes is particularly important. For convenience of expression in the subsequent sections of this article, an abnormal node can also be called a failure node.