## 3 Comparison of Telecommunications Technologies to Support the Protection Scheme  
One of the key elements for a correct and efficient management of a SG is the SCS. A lot of work has been done in the past regarding the technological choices for a SCS, but the suitability of different solutions for information exchange when a fault occurs in the distribution network to operate the switches, especially the CBs, has rarely been investigated. To this aim, in this section some telecommunications technologies of the SCS are reviewed and compared to investigate their suitability for implementing the considered protection scheme. More specifically, these technologies are evaluated in terms of their ability to enable CBs opening with a reasonable delay, since safety issues are the main concerns to be addressed. Figure 2 shows the time evolution of the fault clearing process related to a CB detecting a fault, highlighting the maximum delay time for safety reasons (typical values are around 100 ms), and the time needed to exchange messages between the above CB and the DMS located at the PS. If the message exchanging time duration is greater than the maximum delay time, the CB will open even when not necessary. Therefore, the choice of telecommunications technology is a challenge because it depends on many elements, including the quality of service requirements characterizing the SG, the telecommunications network infrastructures that are already available in proximity of each node of the SG, and the presence of factors that can justify investments in network facilities but that are external to our specific goal of supporting SG management in cases of faults. The following considerations should be taken into account:  
Figure 2: Time evolution of the fault clearing process. 1. the best technological solution for a distribution network located in an urban area could be poor, unfeasible or totally unavailable for a network that is located in a rural area;
2. the distance between a switch and the PS could vary from less than one kilometer up to some tens of kilometers;
3. the distance between two nodes connected to each other can also be very different (from some tens of meters up to a few kilometers), and a direct wireless connection can be obstructed by buildings or natural barriers placed between them;
4. a telecommunications technology could be already installed for data transmissions during normal service conditions;
5. two nodes can be connected by an overhead (plain conductor or in cable) or underground (conductor in cable) line; in the first case the application of the powerline technology discussed below may not be reliable because the electrical line is exposed to highly variable conditions; and
6. a node could be a pole-mounted substation, a kiosk substation (metallic prefabricated, masonry, or reinforced concrete), or a vault substation. With all this in mind, let us now compare the main technological solutions that can be generally applied to a SG, evaluating their appropriateness to the considered case, which is characterized by the peculiarities described above. Let us consider that, for our purposes, the main target of the SCS is to guarantee reliable point-to-point communication channel between each switch detecting the fault and the DMS. Moreover, for security reasons, this connection must respect a requirement in terms of end-to-end delay on the above point-to-point channel when the switch is a CB. In addition, different technological solutions can be adopted in the same SCS according to the specific situation of each node. The first choice to be made is whether to use wireless or wired links. Among wireless technologies, one of the most widely recognized choices to support an SG is the wireless mesh network (WMN) [20], which is a communication network made up of wireless nodes organized in a mesh topology.