## 3 QoD Measurement for NMGs  
As NMGs gained popularity in recent years, they introduced several research topics that require examination. One of these topics is QoD measurement in NMGs. The power engineering community typically uses latency as a metric for QoD measurements, specifically measuring the one-way delay between NMG endpoints. In contrast, the SG proposes two-way control data communication, introducing RTT as a measurable metric of delay. Table 1 highlights the research gap that this paper addresses. We classify papers using physical equipment, e.g., switches, routers, and OPAL-RT, for power and communication networks as real implementations. Communication network simulators, e.g., Network Simulator-3 (NS-3) and OPNET, are not considered real implementations because they partially represent real-life scenarios. We consider online gaming, video streaming (VS), and similar applications as real-life background traffic. We also examine whether papers address network experiences congestion. In [21], the authors propose a communication network emulation model that represents the communication network using Network Simulator-3 (NS-3) to examine communication performance between NMG endpoints. Throughout the real-time simulation, the User Datagram Protocol (UDP) and the TCP are used to transfer NMG control data between MGCC and NMG endpoints under different intensity bit rate traffic levels. The proposed model reveals that TCP causes higher one-way delay and packet loss rates, which affects the QoD between NMG endpoints. However, since background traffic is not injected into the communication network in this paper, the one-way delay remains at a millisecond level. In modern communication networks, various background traffic flows are present. The lack of such traffic is unrealistic and limits the understanding of QoD measurement in NMGs. An Ethernet-based real-time simulation NMG testbed is implemented in [22]. The proposed NMG testbed is comprised of two layers: a power network, which is simulated by the OPAL-RT power network simulator, and a communication network, which is developed using the OPNET networking simulator. This study examines how latency affects the rate of convergence. The authors reveal that latency increases with increased levels of congestion. They also highlight that a 90% level of congestion causes the rate of convergence to slow down in the NMG setting, which indicates that latency between NMG endpoints negatively affects the QoD in NMG control data. The authors of [23] develop an NMG simulation testbed integrating power and communication networks. The NMG testbed employs GridLAB-D for power network simulation and NS-3 for communication network implementation. This study investigates the interdependencies between NMGs and the communication network by evaluating the impact of varying levels of communication delays to the stability of NMGs. The results demonstrate that congested network conditions lead to increased communication delays. These increased communication delays negatively affect the power generation capacity, resulting in power loss. An NMG testbed that employs both wired and wireless communication is simulated in [13]. The authors evaluate the one-way delay between NMG endpoints in home-based and neighbourhood-based networks while varying the bandwidth levels and the number of smart consumers. The authors reveal that one-way wireless communication causes slight variability in one-way delay, which is measured to be greater than that of wired communication. As expected, the one-way delay in both wired and wireless communication is measured to be lower when the available bandwidth is increased. However, the authors do not introduce additional traffic into the communication network, which leads to the one-way delay being measured at very low millisecond levels. One-way delay and packet loss rates in NMG control data are measured under various levels of network congestion in [24]. The paper utilises a real-time testbed that facilitatesreal hardware components.