400G QSFP-DD Transceiver Types
400G QSFP-DD transceivers are defined by the IEEE 802.3bs Ethernet standard and are an evolution of 100G QSFP28 transceivers. On 400G QSFP-DD, 400G Ethernet is achieved with increased data throughput while maintaining the same bandwidth on per per-channel basis. This is due to 100G QSFP28 using NRZ (Non-Return-to-Zero) encoding and 400G QSFP-DD using PAM4 (Pulse Amplitude Modulation 4 levels) encoding. More on that in 100G Single Lambda (100G PAM & Single Lambda).
On 400G QSFP-DD, PAM4 is enabled by a DSP (digital signal processor) that acts like a gearbox to convert 8 electrical signal channels to 4 optical signal channels. Electrical signal interface can be 25 Gbps NRZ or 50 Gbps PAM4, and after passing through the DSP Transceiver Optical signal is 50 Gbps PAM4 and 100 Gbps PAM4, respectively. Thus, 400G QSFP-DD transceivers can have 8 x 50 Gbps or 4 x 100 Gbps optical channels. The number of optical channels is shown at the end of Industry Name and is different per module type. For example, 400GBASE-SR8 has 8x 50 Gbps PAM4 optical transmission channels.
400G Transceiver Types image shows the main 400G QSFP-DD parameters which are sorted by Industry Name:
400G QSFP-DD Transceiver Types:
| Industry Name | Media Type | Max Distance | Data rate | Wavelength | Connectors | Optical Signal | Standard |
|---|---|---|---|---|---|---|---|
| 400GBASE-SR8 | Multi-Mode Fiber | 100m (OM4) | 425 Gbps | 8x850nm | MTP/MPO 16 | 8x50G PAM4 per lane | IEEE 802.3bs |
| 400GBASE-DR4 | Single-Mode Fiber | 500m | 425 Gbps | 4x1310nm PSM | MTP/MPO 12 | 4x100G PAM4 per lane | IEEE 802.3bs |
| 400GBASE-DR4+ | Single-Mode Fiber | 2km | 425 Gbps | 4x1310nm PSM | MTP/MPO 12 | 4x100G PAM4 per lane | IEEE 802.3bs |
| 400GBASE-FR4 | Single-Mode Fiber | 2km | 425 Gbps | CWDM4 1271/1291/1311/1331nm | Double LC | 4x100G PAM4 per lane | 100G Lambda MSA |
| 400GBASE-LR4 | Single-Mode Fiber | 10km | 425 Gbps | CWDM4 1271/1291/1311/1331nm | Double LC | 4x100G PAM4 per lane | 100G Lambda MSA |
| 400GBASE-LR8 | Single-Mode Fiber | 10km | 425 Gbps | LWDM8 1273/1277/1282/1286/ 1295/1300/1304/1309nm | Double LC | 8x50G PAM4 per lane | IEEE 802.3bs |
| 400GBASE-ER4 Lite | Single-Mode Fiber | 40km | 425 Gbps | LWDM4 1295/1300/1304/1309nm | Double LC | 4x100G PAM4 per lane | IEEE 802.3bs |
The easiest way to see differences in technology that is applied is by looking at the Wavelength column. It can be split into five parts – SR8, PSM4, CWDM4, LWDM4, and LWDM8. With the exception of SR8 and LWDM8, which add to lanes or wavelengths used, all of the technology principles are brought over from QSFP28. More on these principles can be read in the 100G QSFP28 module types and main differences article. Additionally, MPO Split channel design is used for shorter distances, and LC Single multiplexed channel design is used for longer distances, which currently are up to 40km with 400G QSFP-DD 80km modules around the corner.