The terms 40G-SR4 (Short Range 4) and 40G-CSR4 (Collaborative Short Range 4) both refer to specific types of optical transceiver modules designed for 40 Gigabit Ethernet (40GbE) connections. While they share similarities, there are some differences in terms of reach and fiber compatibility. Here's a breakdown of the key distinctions:

1. 40G-SR4 (Short Range 4):

• Wavelength: Typically uses four parallel multimode fibers with a wavelength of 850nm.

• Reach: Up to 100 meters over OM3 multimode fiber and up to 150 meters over OM4 multimode fiber.

• Fiber Compatibility: Designed for use with standard multimode fibers.

2. 40G-CSR4 (Collaborative Short Range 4):

• Wavelength: Similar to 40G-SR4, it also typically uses four parallel multimode fibers with a wavelength of 850nm.

• Reach: Provides an extended reach compared to 40G-SR4. The exact reach can vary but is often specified up to 300 meters over OM3 multimode fiber and up to 400 meters over OM4 multimode fiber.

• Fiber Compatibility: Requires the use of bend-insensitive multimode fibers.

The key difference between 40G-SR4 and 40G-CSR4 lies in the reach and fiber compatibility. 40G-CSR4 offers an extended reach, making it suitable for connections over longer distances within data centers. Additionally, 40G-CSR4 is designed to work with bend-insensitive multimode fibers, which can be advantageous in situations where tighter bends or cable management constraints are present.

When selecting between 40G-SR4 and 40G-CSR4, it's important to consider the specific requirements of the networking environment, including the desired reach, fiber type, and any specific constraints related to cable installation. Always refer to the datasheets and compatibility guidelines provided by the transceiver and cable manufacturers for accurate information.