Systems, methods and instrumentalities may be provided for handling a user plane in a wireless communication system. The wireless communication system may be characterized by a flexible air interface. One aspect of the flexible air interface is that transmissions by a wireless transmit/receive unit (WTRU) in the system may have different quality of service (QoS) requirements, such as different latency requirements. The WTRU may adjust its behaviors based on the QoS requirements, e.g., by utilizing preconfigured resources, resource requests, self-scheduling, and/or the like, such that the transmissions may be performed in accordance with their respective QoS requirements.