The diagram illustrates the case of serving in singles. The server must hit the ball so that it hits his own court first (the table on his side of the net), and then the ball can go over or around the net before hitting the table on his opponent's side of the net.
This means that it is technically legal for a server to serve around the side of the net assembly, provided he can curve the ball enough to bring it back on to his opponent's court. This is by no means an easy serve to perform - since the net post is supposed to project 15.25cm outside the side line
Table tennis rules
Table tennis rules
Table tennis rules
Table tennis rules
Table tennis rules