QSFP56 (Quad Small Form-factor Pluggable 56) is a form factor for transceivers and cables used in high-speed data communication applications. The "56" in QSFP56 indicates that it supports a data transfer rate of up to 56 gigabits per second (Gbps) per channel. Since QSFP56 supports four channels, the total potential data rate for a QSFP56 module is 4 x 56 Gbps, resulting in a maximum aggregate data rate of 224 Gbps.

Typically, QSFP56 modules are used in applications such as 200 Gigabit Ethernet (200GbE) and 400 Gigabit Ethernet (400GbE). These higher data rates make them suitable for demanding networking environments, data centers, and other scenarios where high bandwidth is crucial.

QSFP56 vs QSFP28 vs QSFP+

Seen from their industry names, QSFP56, QSFP28 and QSFP+ are very similar in that they share the same QSFP form factor as their postfix shows, and they have the same size as each other. However, their data center and connectivity capabilities are different. Below is a table listing the basic parameters of QSFP56, QSFP28, and QSFP+.

From the comparison chart, it can be distinctly seen that compared with QSFP+ and QSFP28, the QSFP56 form factor performs a higher network speed as 200G QSFP supporting 4×50G channels. While QSFP+ is an evolution of QSFP to support 4×10G channels carrying 10G Ethernet, 10G fiber channel or QDR InfiniBand. It introduced the concept of multiplexing four lanes to increase the bandwidth, capable of handling 40Gbps line rates at 10GBaud NRZ per lane. QSFP28 supports 4×25G channels and contains 4-lane optical transmitter and 4-lane optical receiver as QSFP+ does.

The most significant change from QSFP+ and QSFP28 to QSFP56 is that QSFP56 made the change from NRZ encoding to PAM4 encoding. Though QSFP56 still uses 4 lanes as QSFP28, the modulation is doubled to 50G per channel, which enables more data on existing fiber, accordingly, more suitable for hyper-scale data center networks.