As of my last knowledge update in January 2022, there isn't a standard called "SFP28" or "SFP56." However, I can provide information on QSFP28 and QSFP56, which are related to optical transceiver modules used in high-speed networking. If you meant SFP28, please let me know, and I can provide information on that as well. 

1. QSFP28 (Quad Small Form-Factor Pluggable 28):

• QSFP28 is a form factor for optical transceiver modules that supports data rates up to 100 Gbps (Gigabits per second).

• Commonly used for 100 Gigabit Ethernet (100GbE) applications, including data center interconnects and high-speed networking.

2. QSFP56 (Quad Small Form-Factor Pluggable 56):

• QSFP56 is a form factor that supports higher data rates, specifically 200 Gbps and 400 Gbps.

• Used for 200 Gigabit Ethernet (200GbE) and 400 Gigabit Ethernet (400GbE) applications, providing increased bandwidth for more demanding networking requirements.

Key Differences:

• Data Rates: The primary difference between QSFP28 and QSFP56 is the supported data rates. QSFP28 supports up to 100 Gbps, while QSFP56 supports higher data rates of 200 Gbps and 400 Gbps.

• Applications: QSFP28 is commonly used for 100GbE applications, while QSFP56 is designed for higher-speed networking, addressing the needs of 200GbE and 400GbE deployments.

• Form Factor: Both QSFP28 and QSFP56 have a similar form factor, but the advancements in QSFP56 allow for higher-speed data transmission.

It's worth noting that standards and technologies in the field of optical networking may evolve, and new developments may have occurred since my last update. Always refer to the latest specifications and industry standards for the most accurate and up-to-date information on optical transceiver modules.