400G QSFP-DD & OSFP Transceivers: SR8, LR4, DR4, DR4+ Explained

400G QSFP-DD & OSFP Transceivers: SR8, LR4, DR4, DR4+ Explained

OptechTW

400G QSFP-DD and OSFP Transceivers: Key Variants and Applications

As cloud-scale networks evolve, 400G transceivers have become a critical component in hyperscale data centers, AI clusters, and metro DCI links. This article provides a detailed comparison of 400G QSFP-DD and 400G OSFP modules, including SR8, DR4, DR4+, LR4, and explains their optimal use cases.

QSFP-DD vs OSFP: Understanding the Form Factors

Feature QSFP-DD OSFP
Size Compact (Hot-swappable) Larger (Higher thermal tolerance)
Power Dissipation Up to 12W Up to 16W
Use Case Broad switch compatibility AI/ML intensive computing nodes
Interface Pins 76 60

  • QSFP-DD (Quad Small Form Factor Pluggable - Double Density): Widely used in Ethernet switches.

  • OSFP (Octal Small Form Factor Pluggable): Preferred for NVIDIA AI/ML systems due to better cooling and power handling.

Key Variants of 400G Transceivers

1. 400G QSFP-DD SR8

  • Standard: IEEE 802.3ck

  • Interface: 8x50G PAM4 on MMF

  • Reach: ≤100m over OM4

  • Application: Intra-rack or short-reach interconnects

  • Connector: MPO-16 or 2x MPO-12

  • Power Budget: Low

2. 400G QSFP-DD DR4 / OSFP DR4

  • Standard: 400GBASE-DR4 (IEEE)

  • Interface: 4x100G PAM4

  • Reach: 500m over SMF

  • Connector: MPO-12

  • Use Case: TOR to spine; leaf-to-leaf over single mode fiber

3. 400G QSFP-DD DR4+ / OSFP DR4+

  • Enhanced Reach: 2km over SMF

  • Same Electrical Interface as DR4

  • Connector: MPO-12

  • Application: Inter-building links or extended leaf-spine networks

4. 400G QSFP-DD LR4 / OSFP LR4

  • Standard: 400GBASE-LR4 (4x100G CWDM)

  • Modulation: PAM4

  • Reach: 10km over duplex LC SMF

  • Application: Metro DCI, long-haul links

 Use Case Scenarios for 400G Modules

Application Area Recommended Module Notes
Intra-Data Center (≤100m) QSFP-DD SR8 / OSFP SR8 Lowest latency, MMF
Leaf-Spine (≤500m) QSFP-DD DR4 / OSFP DR4 MPO-12 SMF
Metro DCI (≤2km) DR4+ / LR4 Tunable versions available
Long-Haul (10km) LR4 CWDM and FEC required

Compatibility with AI & Hyperscale Networks

NVIDIA and Arista switches widely support both QSFP-DD and OSFP:

  • NVIDIA Quantum-2 SN5600: Supports OSFP DR4/SR8

  • NVIDIA CX7 NIC (Q112-400G-SR4): For SR4-based backbone

  • Arista 7060X5 / 7060X6: Support both QSFP-DD SR8 and DR4

Conclusion

The selection of a 400G transceiver—whether QSFP-DD SR8, OSFP DR4, or LR4—depends on your use case, fiber infrastructure, and desired reach. High-performance networks require precision in both form factor and optical interface, especially when deployed in RoCE, AI/ML clusters, or metro DCI.

If you’re designing your next high-speed network or upgrading your interconnects, understanding these options will ensure optimal performance and future-proof scalability.

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