It is disclosed a method of providing a content-on-demand service to a user by means of a communication network. The method comprises transmitting a content to a first terminal of the user and determining whether the user wishes to pay the content at a reduced price. In the affirmative, the method further comprises: generating an acknowledge request message and an expected acknowledge message; generating an advertising block including k commercials and the acknowledge request message in such a way that the user is able to answer to the acknowledge request message only after consuming the k commercials; transmitting the advertising block to a second terminal of the user; listening for an acknowledge message from the second terminal; and determining whether the received acknowledge message corresponds to the expected acknowledge message.