Data Center Cabling Introduction -400G

Let’s talk about the short-distance wiring method of 400G optical modules in the data center.

First, let’s take a look at the mainstream packaging modes of 400G optical modules: QSFP-DD and OSFP.

The Chinese name of QSFP-DD is double-density four-channel small pluggable package mode. It adopts 8 channels and supports 25Gb/s (NRZ modulation) or 50Gb/s (PAM4 modulation). It is compatible with the previous QSFP+/QSFP28, and its size is small , high density, suitable for short-distance wiring in data centers;

The size of OSFP is a little larger than QSFP-DD. OSFP is backward compatible with QSFP+/QSFP28 like QSFP-DD, but it needs to use an additional OSFP to QSFP adapter to realize it. It can support 800G backwards and it has its own heat sink , for the telecom market.

Data Center Connection Scheme

The figure below shows the end face density of two MPO/MTP fiber optic jumpers.

MPO/MTP-8F fiber optic jumper is used in SR4/DR4 connection scheme, and MPO/MTP-16F fiber optic jumper is used in SR8 connection scheme.

400G DR4 to 400G DR4 connection solution

400G QSFP-DD/OSFP DR4 optical module connection scheme, deploy an MPO/MTP pre-terminated backbone optical cable between two 400G switches, and deploy an 8-core MPO/MTP optical fiber jumper at the 400G switch end to connect the optical module. Deploy high-density optical fiber distribution boxes (including MPO adapters) between the terminated backbone optical cables and optical fiber jumpers for management.

400G SR8 to 400G SR8 Connection Solution

For the direct connection of 400G QSFP-DD/OSFP SR8 optical modules, deploy an MPO/MTP pre-terminated backbone optical cable between two 400G switches, and deploy a 16-core MPO/MTP-MPO/MTP fiber jumper connection at the 400G switch end 400G optical modules, high-density optical fiber distribution boxes (including MPO adapters) are deployed between pre-terminated backbone optical cables and optical fiber jumpers for management.

400G SR8 to 2*200G SR4 connection solution

The connection between the 400G QSFP-DD SR8 optical module and the 200G QSFP56 SR4 optical module deploys an MPO/MTP pre-terminated backbone optical cable between the two switches, and deploys a 16-core MPO-2*MPO/MTP at the 400G switch end Fiber jumpers are connected to 400G optical modules, 8-core MPO/MTP fiber jumpers are deployed at the 200G switch end, and high-density fiber distribution boxes (including MPO adapters) are deployed between the pre-terminated backbone optical cables and fiber jumpers for management .

Summarize

The 400G SR8 optical module conforms to the IEEE 802.3cm standard and meets the requirements of 70m OM3 and 100m OM4/OM5 transmission links. It uses a 16-core multi-mode MPO connector, 8 transmissions and 8 receptions, and each channel carries a 50Gbps signal when using PAM4 modulation. Using VCSEL lasers, the VCSEL laser market is relatively mature, so it has a price advantage;

400G SR4.2 uses a dual-wavelength 25G VCSEL laser, but it needs to use a 2:1 Mux multiplexer and a 1:2 Demux demultiplexer, which will increase the cost of the optical module;

The 400G DR4 optical module complies with the IEEE 802.3bs standard and meets the requirements of a 500m transmission link. It uses a 12-core MPO connector, 4 sends and 4 receives, and each channel carries 100Gbps signals. The use of more expensive DML lasers or SiPh silicon photonics technology can reduce the power consumption and cost of optical modules, but because silicon photonics technology is currently in the early stage of industrial development, the shipment volume is low, and it cannot form a scale effect.