A Brief Introduction on Double Density QSFP (QSFP-DD)

With the rapid growth of data center and 5G development, density, power limits in servers, switches, and other network equipment are being pushed by rising demand and data volume. Data center is required to support faster processing, more bandwidth, and increased density without sacrificing reliability. In this situation, QSFP-DD came out, which is a new module and cage/connector system similar to current QSFP, but with an additional row of contacts providing for an eight lane electrical interface. In this article, we will introduce you something about QSFP-DD that you may be interested in.

1. What Is QSFP-DD?

QSFP-DD stands for Quad Small Form Factor Pluggable Double Density. What Double Density means? The “double density” means the doubling of the number of high-speed electrical interfaces that the module supports compared with a standard QSFP28 module. QSFP-DD is a “double-density” module and cage/connector system which is similar to the current QSFP system. But QSFP-DD has an additional row of contacts providing for an eight-lane electrical interface. The new optical module will be able to operate 25 Gb/s NRZ modulation or 50 Gb/s PAM4 modulation over 16 pairs of twinaxial conductors or optical fibers to support 200 Gb/s or 400 Gb/s aggregate bandwidth.

2. An Introduction on QSFP-DD MSA Group

QSFP-DD Specification for QSFP Double Density 8X Pluggable Transceiver is currently under development by the QSFP-DD MSA Group. The group includes 13 members which are all the leading vendors in the optical communication industry, like Cisco, Brocade and Finisar, aiming to create a upgraded version of QSFP transceiver, which is called QSFP-DD and is able to support 200G/400G Ethernet.

QSFP-DD MSA Group participants have developed an improved management interface. The MSA project may split into separate management interface and form-factor documents. There is a possibility that the OSFP MSA Group, the uQSFP MSA Group, and the Consortium for On-Board Optics (COBO) will adopt the improved QSFP-DD management interface.

3. QSFP-DD vs. QSFP28

QSFP28, with increased data rates ranging up to 28 Gbps on each of four lanes, supports next-generation 100 Gbps Ethernet and 100 Gbps InfiniBand. Now it is quite popular in datacenter computing, switches, routers, and storage. With enhanced Data Rate applications, the QSFP28 interconnect transmits up to 25 Gbps per-serial lane data rates with excellent signal integrity, EMI protection, and thermal cooling.

The QSFP-DD is similar to the current QSFP, but there are still some differences. If modulated by NEZ, each lane of the QSFP-DD can support data rate up to 25G, thus, it can support a total data rate of 200G. If modulated by PAM4, QSFP-DD transceiver can support data rate up to 400G with each lane supporting data rate of 50G. The MSA group also announced that the QSFP-DD can enable up to 14.4Tbps aggregate bandwidth in a single switch slot, which can definitely satisfy the increasing need for higher bandwidth.

4. 200G QSFP-DD

To achieve 400 Gbps, the interconnect industry is developing next-generation Quad Small Form Factor Pluggable Double Density (QSFP-DD) modules. And Gigalight also took the opportunity to release out the new 200G QDFP-DD in this summer. The 200G QSFP-DD integrates eight data lanes in each direction with 8×25.78125Gbps bandwidth. Each lane can operate at 25.78125Gbps up to 70m by using OM3 fiber or 100 m using OM4 fiber. The module is designed to operate over multimode fiber systems using a nominal wavelength of 850nm. It is a high performance module for short-range multi-lane data communication and interconnection applications. It is four-Channel, pluggable, parallel, fiber-optic QSFP+ SR4 for 100 or 40 Gigabit Ethernet, Infiniband FDR/EDR and applications. This transceiver is a high performance module for short-range multi-lane data communication and interconnects applications.


The QSFP-DD optical transceiver is also forward/backward compatible with QSFP, QSFP28 optical transceiver, AOC/DAC and so on. We believe that the rapid development of QSFP-DD will greatly benefit on the whole optical interconnect and communication industry. Let’s wait and see what will happen in the future.




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