SR (Short Reach) and LR (Long Reach) are optical designations commonly used across various module types (such as SFP+ /SFP28, QSFP /QSFP28). They are not brand-specific; they are industry conventions that help communicate intended transmission reach. Some are responsible for connections of a few meters between server racks, while others bear the heavy responsibility of spanning tens of kilometers across a city. This difference is the most fundamental dividing line. They look almost identical, but their internal structures are vastly different. SR. Long distance optical modules address the needs of long-distance transmission, such as urban area network construction and synchronous fiber optic networks.