Choosing the right QSFP28 module requires matching fiber type, reach, switch compatibility, and deployment needs to ensure optimal 100G connectivity in data centers.

Understanding QSFP28

QSFP28 (Quad Small Form-factor Pluggable 28) is a hot-pluggable optical transceiver designed for 100 Gigabit Ethernet (100GbE) using four 25G NRZ lanes, delivering a total of 100 Gbps. Each lane can operate independently, and the module supports breakout into four 25G connections. QSFP28 modules comply with QSFP28 MSA and IEEE 802.3bm standards, typically consuming 3.5–4.5 W of power and supporting Digital Diagnostic Monitoring (DDM) for real-time monitoring of temperature, voltage, transmit/receive power, and laser bias current .

Key Selection Criteria

1. Fiber Type
   • Multimode Fiber (MMF): Used in SR4 modules for short distances (up to 70m on OM3, 100m on OM4, 150m on OM5) with MTP/MPO-12 connectors. Ideal for top-of-rack switching and intra-rack links .
   • Single-Mode Fiber (SMF): Used in LR4, CWDM4, or Single Lambda modules for longer distances (typically up to 500m or more). Requires MTP/MPO-12 connectors and is suitable for intra-data center or campus links .
2. Reach Requirements
   • Short-reach (SR4) for intra-rack or row connections.
   • Medium-reach (LR4/CWDM4) for longer intra-data center or campus links.
   • Ensure the module's reach matches your fiber infrastructure to avoid costly deployment errors .
3. Switch Compatibility
   • Confirm that your switches support QSFP28 ports. While QSFP28 modules may fit QSFP+ ports physically, signaling differences can prevent proper operation. QSFP-DD ports are backward-compatible with QSFP28 for future 400G upgrades .
4. Breakout and Port Density
   • QSFP28 supports breakout into four 25G lanes, enabling flexible network design.
   • Consider whether you need direct 100G links or multiple 25G connections for server-to-leaf or spine-leaf architectures .
5. Power and Thermal Considerations
   • Typical QSFP28 modules consume 3.5–4.5 W. Ensure your switch or chassis can handle the thermal load, especially in high-density deployments .
6. Future-Proofing
   • Evaluate whether your data center may upgrade to 400G or 800G. QSFP-DD modules support higher speeds while maintaining backward compatibility with QSFP28 .

Practical Selection Steps

1. Verify Form Factor: Confirm QSFP28 is supported by your switches and routers.
2. Match Fiber Type and Reach: Align module type (SR4, LR4, CWDM4) with existing fiber infrastructure.
3. Check Power Budget and Thermal Limits: Ensure modules operate within switch specifications.
4. Consider Breakout Needs: Decide if you need 100G links or multiple 25G lanes.
5. Validate Vendor Compatibility: Confirm modules are compatible with your switch vendor to avoid interoperability issues.
6. Plan for Future Upgrades: Consider QSFP-DD or PAM4 options if higher speeds are anticipated .

Conclusion

Selecting the right QSFP28 module involves a careful balance of fiber type, reach, switch compatibility, power, breakout requirements, and future scalability. Following a systematic selection process helps prevent costly mistakes, ensures high-speed connectivity, and supports intelligent computing center architectures efficiently.