## 5 SSFXG Architecture and Basic Interactions
### Anonymous Untraceable Voice Call Services  
Previous generations of wireless communication NWs have evolved towards Voice over Internet Protocol (VoIP) NWs [24], transforming how subscribers communicate. VoIP enables subscribers to transmit voice calls over the internet faster and more efficiently than traditional phone lines. Accordingly, the SSFXG model proposes a VoIP application that enables NW subscribers to communicate with each other anonymously, free from tracking or communication packet interception. SSFXG offers a global service where digital agents acting on behalf of NW subscribers can create obfuscated cascaded VPN-like tunnels, enabling secure and anonymous connections between subscribers. This model employs a multi-step approach to provide an anonymous and untraceable voice calling service, illustrated in Figure 5. To prevent the in-service NW providers' activity tracking, the proposed model utilizes a common SC platform to handle voice call connectivity establishment for NW subscribers anonymously and untraceably. A dedicated SC controller, which manages phone call requests among available NW subscribers, is therefore assumed to be deployed. Figure 4: NW service provisioning bidding scenario. In a federated wireless communication NW, initiating and managing a phone call between two NW subscribers is a sophisticated process designed to ensure security, privacy, and seamless functionality. This process begins with NW Subscriber A identifying NW Subscriber B using the public identifier assigned during the initial subscription phase. NW Subscriber A's SC forwards the call request to the SC controller through encrypted VPN tunnels. The SC controller then relays this request to NW Subscriber B's SC, which notifies NW Subscriber B about the incoming call request, providing relevant details about the caller. NW Subscriber B has the option to either accept or decline the call. If NW Subscriber B rejects the request, their SC terminates the process and informs the SC controller. Subsequently, the SC controller sends a notification to NW Subscriber A's SC, ensuring that the caller is promptly updated about the rejection. In cases where NW Subscriber B does not respond within a predetermined time limit, the SC controller triggers a timeout mechanism. This mechanism sends a series of cascaded notifications to NW Subscriber A, indicating that the call request has expired. These measures ensure that resources are managed efficiently and subscribers are kept informed of the call status. If NW Subscriber B accepts the call, their SC interacts with NW Subscriber A's SC via the SC controller to establish a secure communication channel. The SC controller dynamically creates a disposable voice service agent, which acts as a temporary computational container for managing the session. This agent is designed with tamper-proof logic to ensure the integrity and security of the call. The agent establishes an encrypted VPN-like tunnel between the SCs of both subscribers, which is then extended to their respective devices. This setup ensures that all voice data transmitted during the call remain confidential and protected from unauthorized access. The voice service agent is synchronized with the duration of the call and is automatically deleted once the session ends. This ensures that no residual data or vulnerabilities remain, maintaining the privacy and security of the subscribers. The SC controller efficiently releases all resources associated with the call, including dismantling the encrypted tunnel and terminating the agent. This streamlined process not only enhances security but also optimizes the use of NW resources. This approach offers numerous benefits. The process ensures a high level of security and privacy for all communications by utilizing encrypted VPN-like tunnels and tamper-proof agents. The dynamic creation and deletion of service agents allow for efficient resource allocation, preventing wastage.