With the continued growth in AI computing demand, data center networks are rapidly transitioning from 400G to 800G. However, many data centers still deploy 100G and 200G server network interface cards (NICs), making it difficult to upgrade all servers to 800G in the short term. How can high-speed connectivity between an 800G switching network and 200G servers be achieved while retaining existing server infrastructure?
When an 800G port is broken out into four independent 200G ports, how should the optical transceivers be selected and the links connected? This article provides a brief overview.
1. Interconnection Principles
Consider an MQM9790-NS2F switch equipped with 800G OSFP VR8 optical transceivers and servers equipped with ConnectX-7 NICs (model MCX715105AS-WEAT). When an 800G port needs to be broken out into four 200G links, which optical transceivers should be used on the 200G side?
800G OSFP VR8 transceivers typically use eight 112G PAM4 electrical lanes, whereas traditional 200G QSFP56 transceivers use a four-lane 50G PAM4 architecture. Since their per-lane data rates differ, direct interconnection cannot be achieved through port breakout alone.
The next-generation 200G QSFP112 VR2 transceiver uses two 112G PAM4 electrical lanes, matching the per-lane data rate of 800G VR8. By breaking out an 800G port into four independent 200G links, each 200G link uses two 112G electrical lanes, enabling lane-rate compatibility between the two ends and supporting high-speed interconnection.
2. 200G QSFP112 VR2 Optical Transceiver Overview
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Wavelength: 850 nm
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Transmission distance: 30 m over OM3 / 50 m over OM4
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Connector: Single MPO-12/APC
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Electrical interface: 2 × 112G PAM4 SerDes
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Operating temperature: 0°C to +70°C
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Compliance: QSFP112 MSA and CMIS 4.0
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Environmental compliance: RoHS
3. 800G to 4×200G Breakout Application
The dual-port 800G OSFP VR8 optical transceivers in the MQM9790 switch connect to single-port 200G QSFP112 VR2 transceivers installed in four ConnectX-7 NICs at the other end. The connections are made using two 8-fiber MPO/APC 1-to-2 fiber breakout cables.
