## 5 Results  
### Considered FttC Realistic Scenario and Improvements of FttC Access Network  
For evaluation purposes, the Italian FttC network scenario is considered. The statistics of the distances of Cabinets from the respective COs and the distances of distributors from the serving Cabinets have been split into three groups of cities according to the residential population. We distinguish cities with number of inhabitants greater than 300,000 (group 1), cities with inhabitants between 50,000 and 300,000 (group 2) and those lower than 50,000 (group 3). To be more specific, group 1 includes large cities such as Rome, Milan, Turin, Genoa, and Florence. In Figure 3, we plot the cumulative distribution function (CDF) of the distances of distributors for the three groups. As shown in the Figure, the Italian secondary network is _short_ i.e., the probability of having distributors at distances shorter than 300 m from their Cabinets is lower than 50% (group 3) and about 60% for groups 1 and 2. The target distance value of 300 m is usually considered for the vectoring to be effective. In fact, vectoring is a short distance technique, usually loosing its effectiveness at distances from the Cabinet greater than 450 m-500 m.  
Considering the ratio between the total number of distributors and the sum of areas (in km\({}^{2}\)) of the cities in each group, we obtain an indication of the average spatial density of the distributors for each group of cities. These values are reported in Table 1 where we have also indicated the density of the Cabinets. As shown in Table 1, connecting 5G nodes to Cabinets only does not allow to obtain the density of access points, which is required for ultra-dense networks as defined in the Introduction. Instead, the possibility of connecting 5G nodes to Cabinets and distributors too, allows reaching the density required for ultra-dense network deployment for cities in group 1, at least. The FttC network for cities in group 2 can support dense and for some cities even the ultra-dense deployment. Concerning cities \begin{table}
\begin{tabular}{|l|l|l|l|} \hline  & Group-1 & Group-2 & Group-3 \\ \hline
**Cabinets per km\({}^{2}\)** & 13.1 & 3.3 & 1.5 \\ \hline
**Distributors per km\({}^{2}\)** & 104.8 & 36.2 & 14.2 \\ \hline \end{tabular}
\end{table} 
Table 1: Average density of distributors for each group. Figure 3: CDF of the distances of the distributors from the Cabinet in the case of FttC for Italy. in the group 3, characterized by a reduced density of Cabinets and longer distances of the distributors from the respective Cabinet, FttC can provide support for dense network, only. For FttC to gradually evolve toward an all-fiber optical implementation, we consider two updating strategies consisting in moving the Cabinets closer to distributors and gradually substituting copper pairs connecting some distributors with the optical fiber. To describe two considered strategies we consider one Cabinet and one cable from it. We assume \(n_{D}\) distributors are positioned along the cable at distances \(d_{i}\), \(i=1,\ldots,n_{D}\). We consider a reference distance \(d_{OE}\) and we assume \(d_{k-1}-d_{OE}<0\) and \(d_{k}-d_{OE}>0\) for some \(k\leq n_{D}\). Then, in the _first update strategy_ we add one Cabinet at distance \(d_{OE}\), which is connected to the CO with optical fiber. In order to reduce digging costs, we can safely assume that the deployment of the new optical fiber starts from the old Cabinet premises and extends up to \(d_{OE}\). Since digging follows the trace of the original cable, even all the distributors at distances \(d_{1},d_{2},\ldots,d_{k-1}\) can be connected to the old Cabinet by optical fiber then removing copper pairs and adding, for example, a G.fast device at the distributor to connect users and the radio node with copper pairs. As an alternative, radio ports can be connected with the optical fiber. The copper pairs in the cable attached to the distributors at distances \(d_{k}>d_{OE}\) are then connected to the new installed Cabinet.