There is provided a mechanism for reporting buffer status information to a communication network control element when transmission via both a licensed and an unlicensed spectrum is conducted and offloading of traffic is executed. After an offloading value indicating the amount of traffic which can be offloaded from a transmission over a licensed spectrum to a transmission over an unlicensed spectrum is estimated, the UE determines a buffer size of at least one transmission buffer used in a transmission over the licensed spectrum and the unlicensed spectrum. Then, buffer status information is sent to the eNB wherein the estimated offloading value is considered. The eNB can then allocate resources for the transmission over the licensed band while benefits by the offloading to the unlicensed band are considered in the resource allocation.