In the field of 400G optical modules, Cisco’s QDD-400G-FR4-S and QDD-4X100G-FR-S are both QSFP-DD packages, support PAM4 modulation and FEC functions, and power consumption is less than 12W412. However, there are significant differences between the two in terms of architecture design, interface type and applicable scenarios, which directly affect deployment choices.
Core Architecture and Interface Differences
Channel design
QDD-4X100G-FR-S: uses 4-channel independent transmission (4×100G-FR1), each channel has a wavelength of 1310nm, and realizes parallel optical signal transmission through the MPO-12 interface.
QDD-400G-FR4-S: Using wavelength division multiplexing (CWDM4) technology, multiplexing 4 wavelengths (1271/1291/1311/1331nm) on a single pair of optical fibers, and transmitting 400G signals through a duplex LC interface.
Physical interface
QDD-4X100G-FR-S needs to be paired with MTP/MPO-12 APC patch cord (multiple optical fibers connected in parallel), which is suitable for high-density wiring environments.
QDD-400G-FR4-S uses a duplex LC interface (single-pair optical fiber serial transmission), which is compatible with the existing data center LC wiring architecture and reduces transformation costs.
Transmission Performance and Application Scenario Comparison
| Parameter | QDD-4X100G-FR-S | QDD-400G-FR4-S |
| Transmission distance | 10km (single-mode fiber) | 2km (single-mode fiber) |
| Maximum rate | 425Gbps (4×106.25Gbps PAM4) | 425Gbps (aggregated 400G) |
| Typical applications | Data center core layer interconnection, 100G split expansion | Short-distance computer room interconnection, LC architecture upgrade |
Breakout capability
QDD-4X100G-FR-S supports splitting into 4 independent 100G links (such as connecting 4 100G switches) to improve port utilization.
QDD-400G-FR4-S does not support splitting and is only used for end-to-end 400G connections.
Deployment cost impact
MPO-12 cabling (QDD-4X100G-FR-S) requires dedicated jumpers and patch panels, with higher initial costs, but suitable for future expansion.
LC interface (QDD-400G-FR4-S) reuses existing fiber resources and is more suitable for low-cost upgrades within 2km.
How to Choose?
Choose QDD-4X100G-FR-S if: long-distance transmission over 10km is required, 100G links are planned to be split, or the network architecture is based on MPO cabling.
Choose QDD-400G-FR4-S if: transmission distance ≤ 2km, LC interface compatibility is sought, or the complexity of MPO fiber management is avoided.
Compatibility tips: Both are Cisco certified 400G QSFP-DD, but it is necessary to pay attention to the switch port support type-MPO ports cannot be inserted with LC modules, and vice versa.
Conclusion
QDD-4X100G-FR-S is known for its splitting capability and long-distance coverage, and is suitable for backbone network expansion; QDD-400G-FR4-S wins with the convenience of LC interface, becoming an ideal choice for short-distance data centers. When making decisions, it is necessary to weigh the current wiring situation, transmission distance and future expansion needs to maximize the performance and return on investment of 400G technology.
