## 2 Wireless Telecommunication Networks for Critical Infrastructures and Emergencies
The architecture of this implementation of the two interconnected central data systems was supervised by the software-defined data center (SDDC) software, i.e., Asterisk V16.1, which defines area networks with the ultimate goal of eliminating interconnection issues between these systems. To conduct their test scenarios, they used a server with the Asterisk operating system, which could record the calls made. For each scenario, they conducted 150 and 300 calls, respectively. The call quality with a bit rate of 80 Mbps was stabilized by applyinga policy of traffic prioritization for IP calls. However, during high demand for calls, where there was a greater increase in call volume, the bitrate for the 150 calls scenario dropped to 52.12 Mbps, while for the 300 calls scenario, it was maintained at an average of 44.80 Mbps. Moreover, we should not overlook the possibility of making VoIP calls through 4G technology. Specifically, calls in 4G technology are made using mobile phones. These calls are known as VoLTE calls. To ensure good quality in VoLTE calls, further performance analysis is needed. [PERSON] et al. [9] performed such measurements, analyzing and comparing the performance in 4G networks. They presented results on bandwidth availability, jitter performance, and voice delay during VoIP calls. Through comprehensive analysis, they concluded that both jitter and delay values met the QoS requirements for implementing a VoIP calling system over a 4G-LTE network. In 2018, [PERSON] et al. [10] introduced CoLTE, an open-source implementation for private networks based on OAI, which is compatible with Debian 9 and Ubuntu 18.04 LTS. CoLTE is a lightweight LTE core network designed for small-scale community LTE networking, featuring on-site Evolved Packet Core (EPC) deployment with minimal cellular radio stations (eNodeBs). Its primary function is establishing a prepaid network management system that enables usage-based billing or IP traffic rate charging. By collocating the EPC in the field, CoLTE provides high-bandwidth local connectivity, supporting custom SIM cards for user coverage and LTE security. The implementation successfully served over 40 active users, offering cost-effective solutions, and ensuring economic sustainability by covering both operational and capital expenses. In mid-2020, [PERSON] et al. [11] established a private network supporting closed-loop control and video applications. The network consisted of three main components: a radio access network (RAN), a core network (CN), and a slicing gateway. They examined three applications: closed-loop control, involving a robotic arm receiving activation commands; event-driven control, where a human operator controlled a robotic arm; and video streaming using a commercial handset. The implementation used a USRP Ettus X310, Ubuntu 16.04, and the OpenAirInterface Public License V2.1. software, and Open Cells SIM cards. The demonstration showcased the successful coexistence of diverse applications with software-defined radio slicing. [PERSON] et al. [12] introduced a coexistence scheme for private LTE networks in unlicensed spectrum alongside co-located Wi-Fi networks. Through utilizing LTE configurations and the Wi-Fi spectrum, the paper demonstrates that private LTE can successfully adapt to the presence of Wi-Fi, catering to both upload and download scenarios. Thus, the flexibility of LTE in adjusting to Wi-Fi requirements is emphasized in this implementation. In summary, the reviewed studies exhibit both commonalities and distinctions in their approaches to communication network enhancement. Among the similarities, multiple investigations prioritize the utilization of modern technologies such as VoIP, SD-WAN, LTE, and Wi-Fi to elevate communication efficiency, quality, and reliability, especially in demanding scenarios like natural disasters or remote work environments. Additionally, there is a prevalent emphasis on ensuring QoS delivers satisfactory user experiences for voice and video communication.