400G

400G refers to a data communication rate of 400 gigabits per second (Gbps). In networking, it is commonly associated with 400 Gigabit Ethernet (400G Ethernet), a set of standards and technologies designed to move data centers, service providers, and telecom networks at higher speeds than previous generations. 400G does not designate a single protocol; rather, it encompasses multiple physical layer implementations and channel configurations that deliver 400 Gbps over fiber or copper links of varying distance.

Common approaches to achieve 400G include aggregating four 100G lanes (often NRZ) or two 200G lanes (often PAM-4), with options for long‑haul, metro, and data center interconnects using coherent optical transmission and wavelength-division multiplexing. Shorter‑reach links may use multi‑mode fiber or copper‑based direct‑attach copper (DAC) or active optical cable (AOC) solutions, while longer links rely on coherent optics with dispersion management.

Standards and form factors: IEEE 802.3 has defined 400G Ethernet interfaces and corresponding optical modules; practical implementations use pluggable form factors such as QSFP-DD and OSFP, and often rely on fiber types including single‑mode fiber for long reach and, for shorter reaches, multimode fiber. In optical transport, 400ZR and related specifications guide interoperable coherent 400G links across networks.

Deployment and impact: 400G has become a key option for data centers to scale interconnect bandwidth within and between campuses, and for service providers building high‑capacity backbone networks. Tradeoffs include power consumption, heat, cost of optics, fiber availability, and the need for advanced switching or routing hardware. Adoption progressed through the late 2010s and into the 2020s, with a growing ecosystem of devices, transceivers, and cables.