# Design and Implementation of a Passive Optical Network for a Small Town +
## 3 Methodology
### Traffic Aggregation and PON Dimensioning  
Using the above service profile, we next calculated the aggregate bandwidth demand on each segment of the PON. The GPON standard provides a total downstream capacity of 2.488 Gbps (and 1.244 Gbps upstream) per PON port [17]. This capacity is shared by all users on that PON in a point-to-multipoint fashion. We considered a conservative worst-case scenario where many users are simultaneously active at peak rates, as well as more realistic \begin{table}
\begin{tabular}{c c c} \hline \hline
**Service** & **Bandwidth Requirement** & **Notes/References** \\ \hline \multirow{2}{*}{High-Definition IPTV} & \(\sim\)5–8 Mbps per stream & \multirow{2}{*}{e.g., one HD channel uses \(\sim\)5–8 Mbps} \\  & (H.264/AVC compressed) & \\ \hline \multirow{2}{*}{Ultra-HD/4K IPTV} & \(\sim\)20 Mbps (or more) per stream & Higher-resolution video requires \\  & (HEVC compressed) & \(\sim\)20–25 Mbps \\ \hline \multirow{2}{*}{VoIP telephone (G.711)} & \(\sim\)0.1 Mbps per call (bidirectional) & Each phone line \(\approx\) 100 kbps \\  & & up/down \\ \hline \multirow{2}{*}{Internet data (web, OTT)} & Variable; up to subscribed rate & Web browsing, OTT streaming, etc., \\  & (e.g., 50–100 Mbps) & up to plan speed \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Typical user service profiles and bandwidth requirements per subscriber. typical usage scenarios. In a worst-case scenario, for example, 32 subscribers each using 100 Mbps (e.g., multiple video streams plus data) would amount to an aggregate demand of 3.2 Gbps, which exceeds the 2.488 Gbps GPON downstream capacity. However, such synchronization of peak usage is highly unlikely in practice. Instead, network planning relies on statistical multiplexing and an oversubscription ratio--not all users will utilize their maximum bandwidth at the same time [18]. For instance, if 32 users each have up to 100 Mbps service, empirical studies show the actual concurrent usage might only reach ~75% of the GPON capacity or less [18]. In one real deployment, over 80% of subscribers subscribed to 10-20 Mbps plans, and the measured GPON port utilization stayed below 75% [18], indicating significant headroom. This justifies designing with a moderate oversubscription (e.g., on the order of 1.3-2\(\times\)) to efficiently use the fiber capacity. We dimensioned each PON segment such that the expected peak aggregate traffic remains at or below the GPON throughput, with some safety margin. Table 2 illustrates the traffic aggregation for the model PON segment in our design. In this example, a two-tier splitting architecture is assumed (details on splitters are in the next section), with 16 users per splitter in a building and 64 users on the entire PON port. Even if each user averages around 10 Mbps (e.g., one HD stream or heavy web use) during the busy hour, the total downstream traffic would be ~160 Mbps on each 1:16 splitter leg and ~640 Mbps at the OLT for 64 users. This is well below the 2488 Mbps GPON capacity (about 26% utilization), leaving a substantial margin for occasional bursts where some users hit higher rates. In a more extreme case, where each of the 64 users pulls ~39 Mbps concurrently (summing to ~2.5 Gbps), the GPON downstream link would just reach saturation; but the probability of all users sustaining such high throughput simultaneously is very low. We also ensured the upstream dimensioning (1.244 Gbps total) can accommodate typical upload demands, which are generally much lower per user (even 4K video upstream or heavy cloud backup are a fraction of download traffic). The GPON dynamic bandwidth allocation (DBA) mechanism further helps manage and prioritize bandwidth sharing among ONTs. As shown in Table 2, under typical conditions the GPON throughput exceeds the actual demand and, even if demand rises (more users or higher usage per user), the network can accommodate it up to the engineered limits. For our design, we targeted a maximum of 64 users per GPON port.