Optical Modules FAQs — Part 2

3 min readSep 15, 2023

In the dynamic realm of optical networking, real-world challenges often test the capabilities of both original equipment manufacturer (OEM) and third-party modules. These challenges encompass issues like unresponsive ports, fluctuating links, CRC errors, packet loss, module failures, and sudden downtimes. To assist and enlighten our community, we’ve compiled essential answers to these common queries:

Q1: High Prices of OEM Modules — Are They Justifiable? Do You Really Need Them?

A1: The soaring prices of OEM modules may raise eyebrows, with a part of the cost aimed at providing assurance, and another part for profit. Yet, OEM modules indeed guarantee superior quality and compatibility, potentially avoiding disruptive issues. Juggling various third-party modules based on cost alone can lead to complications. Some third-party optical modules maintain robust quality control and compatibility testing. The choice depends on your priorities and operational capabilities.

Q2: Manufacturer Size — Does Bigger Mean Better Quality?

A2: For well-established modules, the difference between large and small manufacturers is subtle, mostly evident in extreme cases. Regardless of size, it’s crucial that both manufacturers ensure compatibility with your specific equipment.

Q3: AOC Compatibility Troubles — Whose Responsibility Is It?

A3: When AOC (Active Optical Cable) connections between different manufacturers don’t function as expected, both parties share the responsibility. To avoid such scenarios, clarify the type of equipment on the other end and whether pre-coding is necessary before procuring AOC/DAC (Direct Attach Cable).

Q4: Deciphering Optical Module Transmission Distance

A4: Optical module and AOC transmission distances are primarily determined by the modules themselves, with equipment playing a smaller role. However, for modules that support Forward Error Correction (FEC), both the module and the equipment must be FEC-compatible to achieve extended distances. For example, without FEC, some 40G single-mode modules can only transmit up to 30km, but with FEC support, they can reach 40km.

Q5: Critical Parameters for Long-Distance Single-Mode Optical Modules

A5: When purchasing 40km/80km optical modules, don’t solely rely on the advertised distance or actual fiber length. Consider both the claimed receiving sensitivity and real-world line attenuation to ensure that the specified 80km optical module indeed performs as expected.

Q6: Demystifying the 1-to-4 Cable

A6: Nearly all 40G QSFP+ ports can be configured to split one 40G connection into four 10G links. Similarly, most modern 100G QSFP28 ports support configuration to split one 100G into either four 10G or four 25G connections. The two types of 1-to-4 cables are DAC and AOC, alongside modules and separate fiber optics.

Q7: Compatibility Codes and Model Differences

A7: Some module compatibility issues may arise due to changes in compatibility code verification mechanisms between different models. Model 2 network cards may necessitate compatibility codes, while Model 1 did not.

Q8: Third-Party Modules and Device Compatibility

A8: Issues with third-party modules not functioning on specific devices may stem from the modules being compatibility-tested with other devices but not the one in question. Compatibility extends beyond coding to various signal specifications.

Q9: Unilateral UP Status — Is This Normal?

A9: It’s common for one end to be UP while the other remains unresponsive. Transmit and receive functions operate independently.

Q10: Tackling Packet Loss and CRC Errors

A10: When encountering packet loss and CRC errors, it’s essential to note that ports receiving CRC errors are receiving them from the other end. Investigate the equipment on the opposite side and the line, particularly if third-party devices are involved.

Q11: Diagnosing Unresponsive Ports

A11: Unresponsive ports can result from various factors such as mismatched auto-negotiation settings, temperature fluctuations, compatibility issues between modules and equipment, incompatibility at either end of the equipment, optical fiber problems, coding discrepancies, FEC settings, excessive optical attenuation, and device-specific behaviors like loop protection and link jitter protection.




GIGALIGHT is an open optical network device explorer focusing on data center & cloud computing, wireless & 5G, and metro & broadcast networks.