40GbE
Understanding 40 Gigabit Ethernet
In the late 2000s, Amazon AWS and Google were building massive data centers. The standard server connection was 10 Gigabit Ethernet (10GbE). When the servers generated more than 10 Gbps of traffic, the switches bottlenecked, and data was lost.
The industry needed a faster standard, but silicon technology was not yet capable of processing 40 Gigabits of data over a single wire. The engineering solution was 40GbE.
The Parallel Architecture Cheat
40GbE is essentially an engineering cheat. Instead of inventing a faster chip, they just taped four slow chips together.
- The standard uses exactly four lanes of 10 Gbps.
- It uses a physical hardware plug called a QSFP+ (Quad Small Form-factor Pluggable).
- Inside the QSFP+ module, there are four separate, distinct lasers firing completely simultaneously down four separate glass fibers (or four distinct colors of light on a single fiber using CWDM).
- The receiving switch catches the four separate 10 Gbps signals and mathematically stitches the data back together into a single 40 Gbps stream.
The Physical Wiring Problem
Because the original 40GbE standard (40GBASE-SR4) physically required four transmitting fibers and four receiving fibers, you could no longer use a standard 2-strand fiber cable.
Data centers were forced to rip out their old cables and install massive, thick MPO (Multi-Fiber Push On) cables containing 12 microscopic glass strands inside a single jacket. This was incredibly expensive and bulky, eventually leading to the death of the 40GbE standard.
Key Equations
40 Gigabit Ethernet (40GbE) is a foundational, high-speed data center networking standard ratified by the IEEE (802.3ba) in 2010. Developed to relieve severe bottlenecking in...
Key specifications:
40 Gbps | 10 Gbps
Power: P(dBm) = 10log(PmW), 0dBm = 1mW
Comparison
| Aspect | 40GbE Spec | Typical Range | Impact | Design Note |
|---|---|---|---|---|
| Primary function | 40 Gigabit Ethernet (40GbE) is a foundat... | Application-dep. | Critical | Verify in sim |
| Operating range | By mathematically bonding four distinct... | Application-dep. | Critical | Verify in sim |
| Performance | Understanding 40 Gigabit Ethernet In the... | Application-dep. | Critical | Verify in sim |
| Integration | The standard server connection was 10 Gi... | Application-dep. | Critical | Verify in sim |
| Trade-off | When the servers generated more than 10... | Application-dep. | Critical | Verify in sim |
Frequently Asked Questions
Is 40GbE still used today?
Rarely. 40GbE is largely considered a legacy technology. As soon as silicon foundries figured out how to push 25 Gbps over a single wire, the industry immediately abandoned the bulky 40GbE standard and transitioned entirely to 25GbE and 100GbE (which is just four lanes of 25G).
Can I plug a 40GbE module into a 10GbE port?
No, the physical sizes are different. A 10GbE SFP+ module is small. A 40GbE QSFP+ module is much wider to accommodate the four internal lasers. However, you can do the reverse using a 'Breakout Cable.' Because 40GbE is literally just four 10G lanes taped together, you can plug a special cable into a 40G switch port that splits the signal into four separate 10G cables, plugging into four separate legacy servers.
Can 40GbE run over copper?
Yes, using 40GBASE-CR4 Direct Attach Copper (DAC) Twinax cables. However, because it requires four parallel lanes of massive copper wires, the physical cable is incredibly thick, rigid, and heavy. It can only be used to connect servers that are sitting right next to each other (less than 7 meters apart) inside the exact same server rack.