The QSFP-DD pluggable transceiver supports quadrupling the bandwidth of traditional QSFP modules, allowing network equipment to keep pace with advances in ASIC technology. The system designed for the QSFP module will be backward compatible with the existing QSFP form factor, providing greater flexibility for end users, network platform designers, and integrators.

The hardware specification of QSFP-DD version 6.2 defines a module and the stack height of the integrated box/connector system and the single height box/connector system. The MSA redefines the range of QSFP shape factors, an industry-leading, multichannel, pluggable form factor commonly used in Ethernet, Fibre Channel, and InfiniBand.

The initially released QSFP can run on 40 Gbps and 100 Gbps network applications, while the current QSFP-DD can aggregate up to 800 Gbps on 8 x 100 Gbps electrical interfaces.

Figure:400G QSFP-DD LR4

QSFP-DD vs. QSFP28 Transceiver, What is the difference?

The QSFP28 has data transfer rates of up to 28 Gbps per channel in four lanes, supporting next-generation 100 Gbps Ethernet and 100 Gbps InfiniBand. It is now prevalent in data center computing, switches, routers, and storage. With enhanced data rate applications, the QSFP28 can transmit data rates up to 25 Gbps per serial channel, with excellent signal integrity, EMI protection, and cooling.

QSFP-DD is similar to the current QSFP, but some differences remain. With NRZ modulation, each channel of the QSFP-DD can support data rates up to 25G, thus supporting a total data rate of 200G. If modulated through PAM4, the QSFP-DD transceiver can support data rates up to 400G, and each channel supports a data rate of 50G. The MSA Group also announced that QSFP-DD could achieve a total bandwidth of up to 14.4 Tbps in a single switch slot, which meets the growing bandwidth requirements.

QSFP-DD MSA Introduction

The QSFP-DD MSA working Group was formed in March 2016 to address the market’s need for next-generation, high-density, high-speed pluggable, backward-compatible module form factors. The MSA Working Group successfully released the 3.0 version of the hardware specification, providing extensive support for the market and overcoming the technical challenges encountered when developing a QSFP28-compatible dual-density interface.

The QSFP-DD specification identifies mechanical, electrical, and thermal management requirements that enable multi-vendor interoperability.

The latest QSFP-DD MSA is version 6.2, which was released on March 12, 2022. It is the ninth revision and update of the agreement since it was first published in September 2016. Version 6.2 of the agreement introduces some changes and enhancements to the specification.

400G QSFP Transceivers: Q&A

Q: What does "SR8", "DR4", "XDR4", "FR4", "LR4", and "LR8" mean in QSFP 400G modules?

A: "SR" refers to short-range, and "8" implies there are 8 optical channels. "DR" refers to 500m reach using single-mode fiber, and "4" implies there are 4 optical channels. "XDR4" is short for "eXtended reach DR4". And "LR" refers to 10km reach using single-mode fiber.

Q: Can I plug a QSFP-DD transceiver module into an OSFP port?

A: No. QSFP-DD and OSFP are totally different form factors. For more information about OSFP transceivers, you can refer to the 400G OSFP Transceiver Types Overview. You can use only one kind of form factor in the corresponding system. Eg, if you have a QSFP 400G system, QSFP-DD transceivers and cables must be used.

Q: Can I plug a 100G QSFP28 module into a 400G QSFP port?

A: Yes. A QSFP28 module can be inserted into a QSFP-DD port (without a mechanical adapter). When using a QSFP28 module in a QSFP-DD port, the QSFP-DD port must be configured for a data rate of 100G instead of 400G.

Q: What other breakout options are possible apart from using the 400G QSFP-DD modules mentioned above?

A: 400G QSFP-DD DACs & AOCs are possible for breakout 400G connections. See 400G Direct Attach Cables (DAC & AOC) Overview for more information about 400G DACs & AOCs.

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