100G QSFP28 transceivers have been widely used in today’s optical communications. The next popularity will be 200G/400G with the rapid growth of data centers. QSFP56 and QSFP-DD are the main form factor types of 200G and 400G Ethernet. Whether you are confused about QSFP28, QSFP-DD, and QSFP56, this article will give an all-around comparison among QSFP28 vs QSFP-DD vs QSFP56, helping you quicking understand these three QSFP types.
What is QSFP28?
QSFP28 is a type of QSFP form factor that uses 4 channels (25Gbps per channel) to support data transfer speeds of up to 100Gbps. The QSFP28 form factor is a compact, high-density, and low power consumption 100 Gigabit Ethernet connectivity option for data centers and other high-speed applications. In recent years, shipments of QSFP28 optical transceivers is increasingly rising with the rapid development of higher bandwidth and speed networks.
The common 100G QSFP28 transceivers include 100G SR4, LR4, CWDM4, and PSM4. Their main specifications are shown below.
Besides QSFP28 transceivers, 100G QSFP28 DAC cable is also popular for short-range applications, including QSFP28 to QSFP28 DAC cable, QSFP28 to 4x SFP28 DAC cable. These cables are typically used to connect two QSFP28 ports within a rack or cabinet with a max distance of 10 meters.
What is QSFP56?
200G optical modules with PAM-4 technology
QSFP56 is a relatively new form factor for data communications, designed to support data rates up to 200Gbps. The QSFP56 transceiver is compliant with the QSFP56 Multi-Source Agreement (MSA). 200G QSFP56 transceiver is an upgraded version of QSFP28. It uses the same physical specifications as prior QSFP28, the biggest improvement is the modulation technology. QSFP56 upgrades the modulation technology by using PAM-4 instead of NRZ of 100G QSFP28. While NRZ needs 8x25Gbps to reach 200Gbps, PAM4 only needs 4×50Gbps to support 200Gbps, so as to save the optical fiber costs and reduce the link loss.
The common 200G QSFP56 transceivers include 200G QSFP56 SR4, DR4, FR4, LR4, and ER4. Their main specifications are shown below.
What is QSFP-DD?
The smallest 400G optical transceiver
QSFP-DD means Quad Small Form-factor Pluggable Double Density, also referred to as QSFP56-DD, which is a next-generation, high-density connector interface for high-performance data center applications. It is compliant with the IEEE802.3bs and QSFP-DD MSA. Different from 4-channel QSFP56 transceivers, QSFP-DD uses 8-channel electrical interface, reaching 200G data rates over 8x25Gb/s NRZ, and also supports 400G over 8x50Gb/s PAM-4, which is the smallest 400G optical module.
Backward compatible with QSFP+, QSFP28, and QSFP56
One of the most significant features of QSFP-DD is backward compatibility. The QSFP-DD connector has the same pinout as the older QSFP connector. It is backward compatible with 40G~200G QSFP type optical modules, including the prior 40G QSFP+, 100G QSFP28, and 200G QSFP56. That is, the existing QSFP+ and QSFP28 transceivers can be inserted into QSFP-DD slots without any adapters. So QSFP-DD is a flexible solution for upgrading current 40G/100G networks to 400G. As a result, QSFP-DD provides a high-performance, high-density, and scalable interface that is compatible with a wide range of existing equipment.
The common QSFP-DD transceivers include 400G QSFP-DD SR8, DR4, FR4, LR4, LR8 and 200G QSFP-DD SR8, PSM8, LR8. Their main specifications are shown below.
Comparison of QSFP28 vs QSFP-DD vs QSFP56
Differences Quick View
The following table concludes the main differences of QSFP28, QSFP-DD and QSFP56.
