The question describes a scenario requiring two GPON ports for upstream transmission. Assuming the device in question has two empty upstream optical ports, such as SFP (Small Form-factor Pluggable) slots, two separate optical modules (transceivers) must be purchased and installed to make these ports operational. These modules are typically sold separately from the main device chassis. Therefore, to utilize two ports, two additional optical modules are required. Note: The specific model P815E-G-E actually has one integrated upstream port, but the question's intent is to test the principle for devices with modular uplinks.

A. One or two additional optical module is required: This is imprecise. To use two ports, exactly two modules are needed, not "one or two".

B. No additional configuration is required. The device already contains the configuration: This would only be true if the device had integrated, non-modular optical ports, which contradicts the premise of needing to configure them.

C. One additional optical module is required: This would only be sufficient to activate one of the two available upstream ports.

1. Huawei S5700 Series Ethernet Switches Hardware Description. Chapter "Pluggable Modules for Interfaces". This document details how SFP/SFP+ ports on Huawei devices require the separate installation of appropriate optical transceiver modules to become functional.

2. Huawei OptiXstar P812E/P813E/P815E/P816E Datasheet. This official datasheet confirms the specified model has a single, integrated GPON upstream port, indicating the model in the question is likely used as a placeholder to test a general principle about modular ports.