1. Introduction  
2. Evolution from Traditional RAN to vRAN  
2.1. Traditional RAN or D-RAN  
2.2. C-RAN  
3. Open RAN Movement and the Related Technologies  
3.1. Open RAN Movement  
3.2. Technologies Related to Open RAN  
4. Projects, Activities, and Standards Related to Open RAN  
4.1. Projects and Activities  
4.2. 5G, 3GPP, and Open RAN  
5. O-RAN Alliance Architecture  
6. Challenges and Future Research Directions  
6.1. O-RAN Alliance Architecture Issues  
6.2. Open RAN Field Issues  
7. Open Source Approaches  
7.1. Interoperability and Security Testing  
7.2. OSC Community Labs  
8. Conclusions