The next generation, 5G wireless access, is going to support a wide range of new applications and use cases, with the capabilities including very high achievable data rate, very low latency, ultra-high reliability and the possibility to handle extreme device densities. To avoid the costly deployment, operation and maintenance of future mobile network, Radio Access Network (RAN) virtualization or Cloud RAN is the answer to the problem. The idea is to move the baseband processing to the data center and run the RAN L1, L2 and L3 protocol layers using the commodity hardware, such as high-performance general purpose processors. An open source software-based LTE implementation, such as OpenAirInterface (OAI), is definitely accelerating the RAN cloudization and also realizing the possibility of low cost LTE network deployment in the future. In this paper, we describe the OAI LTE implementation emphasizing on the user plane data flow. We have successfully emulated over-the-air transmission for 1 UE and 1 eNB LTE network supporting both FDD Band 5 and TDD Band 38. We have also performed a thorough profiling of OAI, in terms of execution time, on the user plane data flow. Our results could be served as the reference for future optimization by open source community.