The key difference between QSFP28 (Quad Small Form-Factor Pluggable 28) and QSFP28 DD (Quad Small Form-Factor Pluggable 28 Double Density) lies in the number of electrical lanes and the potential data rates they can support. Both are form factors used for high-speed data transmission, but QSFP28 DD is designed to provide double the electrical lanes, allowing for higher data rates.

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

• QSFP28 supports a total of four electrical lanes, and each lane operates at a data rate of up to 25 gigabits per second (Gbps).

• The aggregate data rate for a QSFP28 module is typically 100 Gbps (4 lanes x 25 Gbps).

2. QSFP28 DD (Quad Small Form-Factor Pluggable 28 Double Density):

• QSFP28 DD is an enhanced version that supports double the number of electrical lanes compared to QSFP28.

• QSFP28 DD supports a total of eight electrical lanes, and each lane can operate at a data rate of up to 25 Gbps.

• The aggregate data rate for a QSFP28 DD module is 200 Gbps (8 lanes x 25 Gbps).

QSFP28 DD is designed to provide a higher data rate compared to traditional QSFP28, making it suitable for applications that require increased bandwidth, such as 200 Gigabit Ethernet (200GbE) and 400 Gigabit Ethernet (400GbE). The higher density of electrical lanes allows for a scalable solution to meet the growing demands of high-performance data centers and networks.

It's worth noting that while QSFP28 and QSFP28 DD modules share the same form factor, they are not directly interchangeable due to differences in the number of electrical lanes. Always check the compatibility and specifications of your networking equipment to ensure proper use of these modules.