What are the challenges of using 100G QSFP28 modules?

100G deployment introduces new challenges around power, cooling, and infrastructure.

Power Consumption

• 100G modules typically draw 3.5-5W each
• 32-port QSFP28 switch can draw 300W+ just for optics
• Requires larger power supplies
• More heat to dissipate

Thermal Management

• QSFP28 cages need active cooling in high-density switches
• Ambient temperature limits (usually 55°C max)
• Airflow direction critical (port-to-power vs power-to-port)
• Monitor module temperatures via DDM

Fiber Requirements

• 100GBASE-SR4: Requires OM4/OM5 multimode with MPO-12
• 100GBASE-LR4: Duplex LC on SMF, uses WDM internally
• Older OM3 fiber may work but at reduced distance

Breakout Applications

QSFP28 can be split into 4x25G with breakout cables:

• Requires switch support for breakout mode
• Uses MPO-to-4×LC cables (LR4 breakout) or MPO-to-MPO for SR4
• Cost-effective for connecting older 25G devices

Signal Integrity

• 25 Gbps per lane pushes limits of copper traces
• Cable quality matters — quality DAC/AOC vs cheap
• Long DAC cables may not meet BER (Bit Error Rate)

DAC vs AOC vs Optics

• DAC (Direct Attach Cable): Copper twinax, up to 5m, cheapest
• AOC (Active Optical Cable): Fiber-based, up to 100m, no separate modules
• Optical modules: Flexible fiber choice, longer distances

Testing and Troubleshooting

• BER testing more critical than at lower speeds
• FEC (Forward Error Correction) usually required
• MPO polarity must be correct (Type A, B, or C)
• Loopback testing helps isolate module vs fiber issues

Cost Considerations

100G module prices vary drastically:

• SR4 modules: $200-500
• LR4 modules: $500-1500
• ER4 modules: $2000-5000