Online classroom is a communication tool to build a real-time online interactive system on the Internet and transmit video, sound and images between users in two or more places in real time. Users who communicate in class can publish text and voice conversations through the system, observe the video images of the other party at the same time, and display documents, drawings and other physical objects on the whiteboard in electronic form. People who participate in the exchange can annotate on the whiteboard while enjoying the contents of the whiteboard, and the effect is the same as that of the classroom opened on the spot.