A client in a media session periodically transmits a “keepalive” message that indicates that a new amount of bandwidth is requested for the in-progress media session. A bandwidth policy service receives the keepalive message and determines whether the new amount of bandwidth can be allocated to the in-progress media session. If the service determines that the new amount of bandwidth can be allocated to the session, the service transmits a response to the keepalive message that indicates that the new amount of bandwidth has been allocated to the media session. The client receives the response and adjusts the bandwidth utilized by the in-progress session to the new amount of bandwidth.