Why 25G, 50G, and 100G Ethernet Are the Future of Data Center Networking

25G Technology

25G Ethernet was standardized by IEEE in 2016 for cloud data‑center servers, later than the 10G/40G/100G standards. Its main advantage is the use of SerDes technology, a serial communication method that maximizes channel capacity, reduces required pins, and lowers cost while increasing transmission speed.

Most switches currently use 10 GHz SerDes providing 10 Gbps per channel. The newer 25 GHz SerDes makes 25G economically viable, creating a cost‑performance gap with 10G and 40G.

10G vs 25G: A single SerDes channel at 25G delivers 2.5 × the throughput of 10G, and 25G SFP28 modules can reuse existing 10G LC jumpers, avoiding rewiring and saving costs.

40G vs 25G: 40G uses four 10 Gbps fibers (12.5 GHz SerDes) while 25G uses a single SerDes channel, offering higher port density and lower cabling costs.

50G Technology

Introduced in 2018, the 50G Ethernet standard adopts PAM4 modulation and reuses 25G components from 100G networks, cutting cost to about half of 40G while delivering 25 % higher performance.

PAM4 maps pairs of bits into a single symbol, resulting in a 26.5625 Gbaud rate per 50 Gb/s channel. A 1×2×50 Gbaud architecture can provide 100 Gbps using only one laser, a ten‑fold increase over 10 Gbps.

Compared with earlier NRZ technology, PAM4 offers higher transmission efficiency at lower cost, making it popular for high‑speed interconnects.

100G Technology

First released in 2010, 100G Ethernet has been continuously optimized, adopting DWDM technology for long‑distance, high‑capacity transmission, and is gradually replacing 40G in data centers.

DWDM modules enable single‑wavelength transmission over metro networks or up to 1000 km links, and 100G/200G/400G multiplexers simplify multi‑rate, multi‑protocol network upgrades without redesigning the architecture.

Relationship among 25G/50G/100G

These speeds are widely deployed in cloud data centers, allowing incremental upgrades from 10G to 25G, 50G, and 100G without costly rewiring. Before 25G and 50G, 100G upgrades required a 10G‑40G‑100G path, which was inefficient and expensive.

Using 25G as a stepping stone to 100G offers the best cost‑performance, enabling spine‑leaf architectures with 4×25G or 2×50G SerDes channels, reducing both CAPEX and OPEX while preparing the network for future 200G/400G upgrades.

Source: SDNLAB (the original article may be slightly outdated; for reference only).