Optical modules B and C do not have the same transmission distance; Module B typically supports up to 20 km, while Module C can reach longer distances depending on its power class.

Transmission Distance by Module Class

• Module B (Class B+): Has an optical budget of 28 dB, which typically allows a transmission distance of up to 20 km over a single optical fiber .
• Module C (Class C+): Features a higher optical budget of 32 dB, enabling longer transmission distances or support for higher split ratios in GPON networks . Class C++ modules can go even further with a 35 dB budget, suitable for dense or extended networks .

Factors Affecting Transmission Distance

1. Wavelength: Longer wavelengths (e.g., 1310 nm or 1550 nm) experience lower attenuation and can travel farther than shorter wavelengths like 850 nm .
2. Fiber Type: Single-mode fibers (SMF) support longer distances than multi-mode fibers (MMF) due to lower signal loss .
3. Dispersion and Signal Loss: Chromatic dispersion and attenuation reduce effective transmission distance, which is why higher-power modules like Class C+ are used for extended reach .
4. Network Design: Split ratios, connectors, and environmental factors can also influence the maximum achievable distance .

Summary

While both modules are designed for GPON networks, Module B (Class B+) is limited to around 20 km, whereas Module C (Class C+) can support longer distances, making them not equivalent in transmission reach. When selecting modules, it is important to consider the optical budget, wavelength, fiber type, and network topology to ensure reliable performance.