The disclosure provides methods, apparatus and machine-readable mediums relating to buffer status reporting in wireless communication systems. One aspect provides a method performed by a user equipment. The user equipment is configurable to communicate with a radio access node via a plurality of communication protocols, and to communicate with a network node via at least one congestion-controlled application transport protocol. The method comprises: generating a buffer status report comprising an indication of a first amount of data available for transmission from the user equipment, the first amount of data including at least data stored in a buffer for data conforming to the congestion-controlled application transport protocol; and transmitting the buffer status report to the radio access node.