## 3 QoD Measurement for NMGs
The authors examine how different network perturbation levels affect QoD in NMG control data by measuring one-way delay and packet loss rates. The following experimental scenarios are carried out using both wired and wireless communication technologies for NMG control data transmission between NMG endpoints: (1) NMG control data are sent over an Ethernet connection exclusively; (2) the control data are transmitted via a Wi-Fi connection without any interference perturbation; (3) the control data are transmitted over a Wi-Fi connection with continuous interference perturbation that leads to noticeable communication disruption; (4) the Wi-Fi connection experiences persistent high-level interference, resulting in near-total communication disruption during the NMG control data transmission; (5) the control data are sent over a Wi-Fi connection with intermittent interference where interference fluctuates between the levels of cases (3) and (4). As a result, the packet loss rates are found to be the highest when communication between NMG endpoints is almost totally disrupted. The authors also observe that slightly higher one-way delay values occur when a Wi-Fi connection is used, which is expected, as high-level persistent perturbation exists in the connection. However, none of these experiments cause greater one-way delays in NMG control data because the perturbation levels remain stable during the experiments. A small-scale NMG testbed is developed in [25]. The RTT measurement is carried out without injected background traffic. The authors measure the RTTs of NMG control data using two different packet sizes, 1 byte and 109 bytes, in separate experiments. However, these constant packet sizes in NMG control data do not represent real-life traffic, which involves varying packet sizes. Packet size distributions in real-life video streaming applications, as measured in [26], show variability. For instance, packet sizes vary between approximately 100 bytes and 1400 bytes in Google Hangouts, with variance in traffic distribution. The limited packet size variance in NMG control data causes RTTs to be measured low and remain at the millisecond level. In [27], RTT measurement is performed in the presence of various levels of background traffic. The authors design an NMG testbed using real hardware that represents NMG endpoints in a small area network and inject different types of background traffic, including VS. Although control data are transmitted quickly in the small area network, the authors conclude that greater RTTs occur in the presence of high-variance background traffic. A software-defined networking (SDN)-based campus NMG testbed is developed to analyse the communication channels for NMG control data traffic during cyber-physical disruptions [28]. The authors examine the robustness of SDN in NMGs by measuring RTTs of NMG control data. The RTT measurement is performed under two experimental scenarios, including no congestion and constant congestion levels in the SDN channel. The results demonstrate that measured RTTs remain at millisecond levels with the help of SDN infrastructure as NMG control packets are diverted to other paths when the congestion level is increased in the communication links. Nevertheless, only NMG control data are transmitted over the SDN channel, and no additional background traffic injection is considered. One-way delay is measured using either simulation tools or a real-life testbed in many papers. However, there are two main points that limit the realism of QoD measurements in current papers. First, NMGs are designed to transfer control data bidirectionally so that the RTT measurement gives a better understanding of data exchange between NMG endpoints. Second, simulation tools simulate real-life scenarios in NMGs, but they are not capable of representing them effectively.