Maximum bandwidth of 100Mbps optical module

A 100Mbps optical module, such as a 100BASE-FX SFP, provides a nominal full-duplex bandwidth of 100Mbps, but actual throughput may be slightly lower due to protocol overhead and network conditions.

Nominal vs. Actual Bandwidth

A 100BASE-FX SFP transceiver is designed to transmit data at 100Mbps over multimode fiber, typically using a 1310nm wavelength and 4B/5B encoding . In full-duplex mode, it can theoretically achieve 100Mbps in each direction simultaneously, effectively allowing 200Mbps aggregate traffic. However, the actual usable bandwidth is slightly lower because of:

• Ethernet frame overhead: Headers, preambles, and inter-frame gaps reduce net data throughput.
• Error correction and retransmissions: Any packet loss or errors on the fiber link can reduce effective throughput.
• Network device limitations: Switches, routers, or media converters may introduce latency or processing delays. In practice, a 100Mbps optical module typically delivers around 95–98Mbps of usable data throughput under optimal conditions .

Factors Affecting Performance

1. Fiber Type and Distance: Multi-mode fiber is suitable for distances up to 2 km, while single-mode fiber can extend further. Longer distances or poor-quality fiber can slightly reduce effective bandwidth .
2. Duplex Mode: Full-duplex operation allows simultaneous send and receive, maximizing throughput. Half-duplex links will experience collisions and lower effective bandwidth.
3. Environmental Conditions: Electromagnetic interference is minimal for fiber, but physical bends, connectors, or splices can introduce signal loss.
4. Device Compatibility: Ensuring the SFP module matches the switch or router port specifications is critical to maintain full 100Mbps performance .

Summary

While a 100Mbps optical module is rated for 100Mbps, the actual data throughput is slightly lower, typically around 95–98Mbps, depending on network overhead, fiber quality, and device performance. Full-duplex operation over short, high-quality fiber links will achieve near-nominal speeds, making these modules reliable for legacy Fast Ethernet networks, industrial applications, and campus links .