Evolution of Data Center Networking: From 100G to 400G and the Future of 200G vs 400G

The Internet now connects over 4 billion users and powers applications such as VR/AR, 16K video, autonomous driving, AI, 5G, and IoT, driving data‑center networks to evolve from early 1 Gb/10 Gb deployments to a "25G access + 100G interconnect" scale.

100G Interconnect – Full‑Box Architecture: Large internet enterprises favor a full‑box design where pods (T1/T2 layers) can be flexibly expanded like LEGO blocks, enabling single‑cluster server counts exceeding 100 k. Although node and optical‑module counts increase, high‑performance forwarding chips lower the per‑bit cost, making the solution attractive for cost‑sensitive data‑centers.

With the advent of high‑capacity forwarding chips and cheaper 100G optics, single‑chip switches now provide 128 × 100G ports, supporting up to 2 000 servers per pod, and the industry is rapidly adopting 100G full‑box architectures while automating deployment to manage the added operational workload.

Next Step – 200G vs 400G: The "25G access + 100G interconnect" model unifies chip selection and accelerates volume production, prompting the question of whether data‑centers should move to 200G or jump directly to 400G.

IEEE Standards: IEEE 802.3 launched the 400G project in 2013 (BWA I) and added 200G in 2015 (802.3cd). The 400G standard (802.3bs) was ratified in December 2017, covering both 400G and 200G single‑mode; the 200G multimode standard followed in December 2018. These standards are now mature and support multiple distances (100 m, 500 m, 2 km, 80 km).

Server Landscape: Analyst forecasts show 100G servers overtaking 50G after 2020, while PCIe 4.0 and upcoming PCIe 5.0 chips from major vendors will support 50G‑100G‑200G‑400G I/O, confirming the shift toward 100G as the mainstream server bandwidth.

Optical Modules – PAM4 Technology: Both 200G and 400G modules adopt PAM4 modulation (4‑level signaling), delivering twice the bit rate of traditional NRZ for the same baud rate. They use a 4‑lane architecture, resulting in similar design cost and power, but 400G offers double the bandwidth, halving per‑bit cost and power compared to 200G.

Market analysis (Omdia) shows 200G modules limited to SR4 (100 m) and FR4 (2 km) with only two vendors, whereas 400G offers five module types (100 m, 500 m, 2 km, etc.) across all top‑8 suppliers, indicating higher maturity and richer customer choices for 400G.

Conclusion: Driven by cost‑sensitive data‑center requirements and the efficiency of PAM4, 400G modules provide a clear advantage over 200G. The industry is likely to skip the 200G generation, with 400G becoming the dominant interconnect technology.