QSFP form factors in comparison

Overview: Form factors of 400G and 200G transceivers

Still, 100G is one of the most prevalent technologies in the ICT market. However, in view of the increasing demand for high bandwidth in applications such as 5G, IoT and cloud computing, the focus is increasingly on higher transmission rates of 200G and 400G.

The QSFP and QSFP-DD form factors are increasingly being used here. The transceivers of the various QSFP generations differ in important features, which we explain below:

QSFP+

QSFP+ (Quad Small Form Factor) is a hot-swappable transceiver. QSFP+ represents a further development of the SFP+ transceiver and can replace four SFP+ transceivers with 4x 10G channels. This leads to a higher port density and thus savings in the overall system.

QSFP28

With the introduction of 100G, the next generation step to QSFP28 was laid. With four separate 25G channels, QSFP28 can be used in 100G networks. In a breakout cable version, it can even be combined with four SFP28 transceivers.

QSFP56

QSFP56 was released in 2017 and represented a significant design advance over previous QSFP modules. The QSFP56 module is designed to support 200G Ethernet. It is equipped with four transmit and receive channels, each capable of operating at 53.125 Gbps, for a combined total data rate of 212.5 Gbps.

850 nm, 1,310 nm, CWDM or LWDM wavelengths are used for data transmission. MPO or LC connectors are used as the optical interface and a 38-pin connector as the electrical interface. In contrast to earlier QSFP form factors, the digital modulation scheme PAM4 is used.

QSFP112

The next level is reached with the QSFP112 module. It complies with the latest QSFP112 MSA specification and supports 112G-PAM4 electrical and optical signaling. Four transmit and receive channels each transmit 106.25 Gbit/s, achieving a total data rate of 425 Gbit/s.

QSFP-DD

QSFP-DD (Quad Small Form Factor Double-Density) is the next evolutionary step in QSFP form factors. The double-density design of the QSFP-DD module essentially multiplies the number of lanes of the electrical interface. While the QSFP28 transmits four lanes at 25 Gbps to achieve a total data rate of 100 Gbps, the 200G QSFP-DD (also: 200G QSFP-28 DD) features an eight-lane electrical interface and supports a total bit rate of 212.5 Gbps.

Using the QSFP-DD's PAM4 digital modulation scheme (also: QSFP56-DD), QSFP-DD operates at 50 Gbit/s, enabling transmission rates of 400 Gbit/s. In addition, this standard is backward compatible with earlier iterations of QSFP modules.

800G as QSFP-DD

QSFP-DD is the smallest form factor for 400G transceivers and offers the highest bandwidth density in the industry. Given the increasing East-West traffic, i.e. the transfer of data packets from one server to another within a data center, and the cost pressure from the associated port density, the QSFP-DD form factor will also quickly establish itself in the 800G range.

The electrical and optical interface is 8x 106.25 Gbit/s (PAM4) and supports 2x 425 Gbit/s or 850 Gbit/s.

The comparison

Conclusion

The QSFP-DD form factor offers significant advantages over the other form factors due to its higher channel count and higher backward compatibility. This also increases its popularity in data center environments, as it allows for higher port density and cost reductions. This paves the way for 400G and 800G applications. 

To learn more about QSFP transceivers, contact your sales representative.