# The Role of Smart Meters in Enabling Real-Time Energy Services for Households: The Italian Case
## 6 Communications Technologies for Real-Time Home Services
### Wireline Technologies  
Wired communications for Smart Grids traditionally include three main technologies: Power Line Communications, Digital Subscriber Line, and Fiber Optical Communications.  
_Power Line Communications_ (PLC) technologies leverage the existing meter power supply cables as a transmission medium, thus avoiding the deployment costs of a new telecommunications  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Wired Technologies**} & \multicolumn{3}{c}{**Wireless Technologies**} \\ \cline{2-4}  & **Cellular Mobile Networks** & **IoT Dedicated Cellular Networks** & **Multi-Tier IoT Architectures** \\ \hline PLC & EC-GSM & wM-Bus & Wi-Fi HaLow (802.11 ah) \\ DSL & LTE-M & LoRa & Bluetooth Low Energy (BLE) \\ Fiber Optical & NB-IoT & SIGFOX & 6 loWPAN \\ \hline \hline \end{tabular}
\end{table}
Table 3: Classification of enabling transmission technologies for smart metering.  
Figure 6: Architecture 4: two-tier model.  
infrastructure [42]. PLC can be categorized into narrow-band and broadband technologies: the former operate over transmission frequencies up to 500 kHz at a low data rate (up to 500 kb/s) and span distances of several kilometers, whereas the latter operate in the range 2-30 MHz and ensure a consistently higher capacity (up to 200 Mb/s) at the cost of a significantly reduced communications range, and are thus typically used only for domestic applications [43]. According to [26], four frequency allocation bands are identified for narrowband PLC:  
* The A-band (3 kHz-95 kHz), reserved for DSOs;
* The B-band (95 kHz-125 kHz), which can be used by all applications without any access protocol;
* The C-band (125 kHz-140 kHz), reserved for IHDs, imposes CSMA;
* The D-band (140 kHz-148.5 kHz), which is specified for alarms and security systems without any access protocol.  
For broadband PLC, the HomePlug standards defined by the HomePlug Powerline Alliance [44] represent the most widely adopted specifications.  
The main issue with PLC is that aged electric wires, as well as the presence of devices that create EM interference, such as transformers, inverters, and LED lamps, significantly limit the communications performance, especially in the narrowband technologies. In addition, neighboring PLC networks can interfere if not properly insulated [45], causing severe performance reduction in terms of lower data rate, increased bit-error, and packet-loss rates, as shown in several studies [46; 47].  
Digital Subscriber Line(DSL) technologies enable digital data transmission over telephone lines, with variable rates depending on the line quality and length. Rates vary from a few hundred megabits per second up to 52 Mbit/s downstream and a few megabits per second upstream with latency in the order of milliseconds. DSL is a popular technology for providing Internet access to home users.  
Fiber Optical Communications, traditionally used in backbone networks, nowadays represent a major technology for accessing networks, thanks to the success of Passive Optical Network (PON) technologies. PONs have therefore been proposed as an optical access architecture to support home multiservice, including smart grids [48]. The advantages of optical communications are the high bitrate on the order of gigabits per second and the long-distance reachability. Moreover, it is completely immune from electromagnetic interferences. On the other hand, the use of such a technology implies a costly installation of a new dedicated infrastructure, which might not compensate for the resulting benefits. It is worth noting that DSOs are increasingly deploying Fiber Optics networks for connecting Primary and Secondary Substations for implementing smart grid services such as anti-islanding techniques and fault detection [49].