AlSki, thank you very much for your detailed answer, it helps me a lot to organize things a little bit. My purpose on this project is to act as the tester for the sender and cover all possible scenarios, either white box or black box. For now, as you said, I imagined only the scenarios I could think of from the black box point of view. We just began an introductory course on testing and the teacher wants to see how our testing skills and thinking evolves in time, after participating at the course. Therefore I am just beginning to learn on how to think things through and cover all sides.