A radio network controller, RNC, keeps control of how many users to configure on a first transmission time interval, TTI, and how many to configure on a second TTI. For example, a method, performed by the RNC, for configuring at least one radio bearer between a radio base station, RBS, and wireless communication devices. The method comprises receiving, from the RBS, a request to perform a TTI switch according to a TTI switch trigger received by the RBS. The received request is analyzed and a grant to perform the requested TTI switch is sent to the RBS.