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400 Gigabit Ethernet (400GbE or 400G Ethernet) is Ethernet operating at a 400 Gb/s MAC data rate. It is a rate, not a particular cable, optical transceiver, or link distance. The physical-layer option must match the medium, reach, and equipment on each link.
What is 400 Gigabit Ethernet?
400GbE is part of the IEEE 802.3 Ethernet family. IEEE defines Ethernet through 400 Gb/s using a common Media Access Control (MAC) specification and management information base, with physical-layer (PHY) options suited to different media. The IEEE 802.3-2022 overview describes Ethernet LAN operation through 400 Gb/s.
The 400 Gb/s figure is the Ethernet MAC data rate, not a promise that an application will transfer data at 400 Gb/s. Protocol overhead, traffic mix, equipment configuration, and the full link path affect application throughput.
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IEEE 802.3bs-2017 added MAC parameters, PHY specifications, and management parameters for both 200 Gb/s and 400 Gb/s Ethernet. IEEE’s 802.3bs-2017 record gives its publication date as December 12, 2017. The IEEE 802.3 Ethernet Working Group’s P802.3bs task-force record says IEEE-SA approved the amendment on December 6, 2017. Approval and publication are separate dates.
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Does 400GbE specify a cable or distance?
No. 400GbE can use PHYs designed for different media and reaches. For example, the IEEE record for IEEE/ISO/IEC 8802-3:2021/Amd 11-2021 describes single-mode optical interfaces with reaches up to 10 km, using 100 Gb/s per-wavelength optical signaling. IEEE’s standards activities page lists 400GBASE-SR4.2 and 400GBASE-SR8 multimode-fiber physical media dependent (PMD) options for reaches of at least 100 m. These are different link types, not interchangeable ways to connect any two ports.
What should you check when choosing a 400GbE link?
Start with the actual path between the devices, then identify a PHY and components that fit it. A 400G label by itself does not establish that an optic, cable, or host port will interoperate.
Quick Recap
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- 400G ETHERNET CONNECTIVITY — Supports 400GbE connections using 4x100G PAM4 signaling. Designed for short-distance links between compatible Ethernet switches and network adapters in data centers, AI clusters and HPC environments.
- OSFP FLAT TOP CONNECTORS — Features OSFP flat-top connectors on both ends for equipment designed to accept this connector style. Verify your device’s port and cooling requirements before ordering.
- PASSIVE COPPER DAC — Integrated twinax copper cable and connectors provide a direct connection without separate optical transceivers or an external power supply. A practical solution for short-reach Ethernet connections.
- 0.5M SHORT-LENGTH DESIGN — The 0.5m (1.64ft) length suits closely positioned equipment, helping reduce excess cable and keep rack connections organized. Check the required routing distance and allow room for gentle cable bends.
- CHECK DEVICE COMPATIBILITY — Requires compatible OSFP ports, supported 400GbE operation and matching cable coding at both ends. This cable does not convert Ethernet to InfiniBand. Confirm the exact switch or adapter model before purchase.
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- Part number: MCX75310AAS-NEAT
- Connector: SFP
- Additional specs: 400GbE, 1-Port
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- Application/Usage: Data Networking
- Application/Usage: Optical Network
- Total Number of Ports: 1
- Connector Type: MPO
- Interfaces/Ports Details: 1 x MPO 400GBase-DR4 Network
- Reach: Confirm the required distance and choose a PHY specified for that reach.
- Medium: Check whether the link uses single-mode fiber, multimode fiber, or an electrical medium.
- PHY standard: Match the physical-layer type at both ends; do not assume two 400G interfaces use the same PHY.
- Lanes or wavelengths: Where relevant to the selected PHY, verify the lane or wavelength arrangement and signaling rate.
- Connector and host support: Confirm the connector, port, and device support for the specific components you plan to use.
- Interoperability: Verify compatibility for the actual equipment and link; a standards name alone does not certify a specific product or guarantee universal compatibility.
What 400GbE does—and does not—tell you
- It tells you: the Ethernet MAC data rate is 400 Gb/s.
- It does not tell you: which cable or optic is required, how far a particular link can run, whether two specific devices are compatible, or what application throughput users will observe.
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