Abstract: In a video on demand (VOD) method and control device using the method, a request for establishing a network topology from the media server is received and the network topology is established. Bandwidth values of several possible transmission routes in the network topology are calculated. A first transmission route with maximum bandwidth is selected and the size of a data cache memory for the client is determined to be smaller or greater than a default value. When the data cache memory size is calculated to be greater than a default value a second transmission route is selected from the transmission routes to effectively transmit more data or faster data. Less network bandwidth is wasted and network efficiency is improved, also ensuring that video of the client plays back smoothly.