What are the differences between OAU and RAU boards?

About the comparisons between OAU and RAU, both are Optical Amplifier Boards:

1.     As a type of optical amplifier unit, the RAU integrates a backward Raman unit, an EDFA unit, and a VOA. Different from an EDFA, the RAU board improves system performance, and amplifies optical signals at the receive end.

2.     But the OAU board, like Huawei TN13OAU103 just amplifies optical signals at the transmit end or receive end.