Viva Voce is like an interview which happens at your Regional Center and conducted by external evaluators expert in there work domain. The main concern of the evaluator is to understand what all the candidate knows in terms of knowledge related to its curriculum and technical industry. So he/she ask you questions related to your project report which includes all expects like, analysis, coding, testing, screen designs, software engineering and any or every concept you study in your degree.
Other than the questions related to the project related areas and the courses concerned, student may be requested to show the demo of the project. Also, you may be told to write the portions of the code for a problem to demonstrate her/his coding capabilities. While appearing for the viva-voce, along with the project report the student should needs to carry the identical copy of the CD of the executable file(s) which s/he submitted at the time of project report.
Its very scoring and in the mean while little tricky as well. So keep your luck rolling.