# Design and Implementation of a Passive Optical Network for a Small Town +
## 3 Methodology
### Splitter Configuration and Optical Budget Considerations  
A critical part of the methodology was deciding the splitter ratios and layout in the network, while ensuring the optical power budget is not exceeded. We evaluated several splitter configurations (single-stage vs. two-stage splitting) consistent with GPON standards and real-world practices [18]. The final design uses a two-level splitting architecture, including an initial splitter in the outside plant (near the local distribution point) followed by secondary splitters closer to the end users (e.g., in building entry points or street cabinets). In our implementation, we employed a 1:4 split at the first level (distribution hub) and then 1:16 splits at the second level (serving individual buildings or blocks of homes). This cascaded arrangement yields an effective 1:64 split per OLT port (4 \(\times\) 16) which, as discussed, can support 64 households. An alternative equivalent configuration is using two cascaded 1:8 splitters (1:8 \(\times\) 1:8 = 1:64) [18]; the choice depends on the available splitter hardware and cabling convenience. We opted for 1:4 + 1:16 since it aligned with the structure of the town (small clusters of up to 16 homes). In cases where fewer users are present, a higher split at first level (e.g., 1:2 feeding 1:32) could also achieve 64 splits, or a direct 1:32 single-stage splitter could be used for a smaller radius--our methodology considered these variants but kept the total split count \(\leq\)64 per PON segment for reliability. Notably, 32-way split configurations are often used in practice as well (many operators limit splits to 1:32 for performance reasons [17]), and our design can be adjusted to 32 users per port (e.g., using 1:8 \(\times\) 1:4 cascade) if lower splitting is desired. After selecting the topology and the splits, we verified the optical link budget to ensure that the optical power levels would remain within the GPON transceiver limits across the reach of the network. GPON optical modules (Class B+ optics as per ITU G.984.2) typically support a 28 dB optical budget, corresponding to about a 20 km maximum reach with a 1:32 split. This budget accounts for fiber attenuation, splitter insertion loss, and connector/splice losses. In our small-town scenario, the furthest subscriber was within ~10 km of the central office, well under the GPON logical reach of 20 km [17]. The fiber attenuation (~0.3-0.35 dB/km for 1310/1490 nm signals) and connector/splice losses (approximately 0.1-0.5 dB each) were summed with the splitter losses to check margin [17]. For a cascaded 1:4 and 1:16 splitter, the worst-case splitter loss is on the order of 14-16 dB (e.g., ~7 dB for 1:4 and ~10 dB for 1:16, plus minor excess loss) [17]. Adding fiber loss (10 km \(\approx\) 3.5 dB) and ~1-2 dB for splices/connectors, the total optical path loss was estimated to be around ~20-22 dB, which is comfortably within the 28 dB budget of Class B+ GPON optics. We also considered the option of increasing the splits to 1:64 or 1:128 in the future; a 64-way split would incur ~18 dB splitter loss, which approaches the limit but could be supported on shorter distances or by using higher-power Class C+ optics (32 dB budget) [19]. For instance, Class C+ modules (commonly available from GPON vendors) extend the budget to ~31-32 dB [19], enough to accommodate a 1:64 split over ~20 km. In our current design, by keeping the splits at 1:64 maximum and the distances moderate, we ensure that the optical power levels at each ONT remain within the sensitivity thresholds for robust operation. This was validated against ITU-T specifications and similar reference deployments [17]. Finally, the splitter ratios were chosen to balance capacity and reach; 1:64 splitting provides efficient fiber utilization and supports the aggregate bandwidth, while staying within the optical budget of standard GPON optics for the given small-town layout.