A method comprising: configuring, in a network node of a cellular communication system, at least one set of available lengths for use in selection of a length of at least one of an uplink control part and a downlink control part of a sub-frame, wherein a symbol length employed and number of symbols in the sub-frame define the granularity for the lengths, and number of symbols in the sub-frame and number of symbols available for each part of the sub-frame limit the at least one set of available lengths; selecting, in the network node, a length of at least one of the uplink control part and the downlink control part of the sub-frame, the length being selected amongst the at least one set of available lengths, the sub-frame comprising the uplink control part carrying at least one of uplink control information and an uplink reference signal and further comprising the downlink control part carrying at least one of downlink control information and a downlink reference signal, wherein the length of the least one of the uplink control part and the downlink control part is selected link direction-wise by assigning resources in the sub-frame for said control part first and allocating remaining resources for data, wherein the uplink control part comprises the uplink signalling information contained in the sub-frame and the downlink control part comprises the downlink signalling information contained in the sub-frame, and causing transmission of a message comprising at least one information element indicating the selected length of the at least one of uplink control part and downlink control part of the sub-frame. configuring, in a network node of a cellular communication system, at least one set of available lengths for use in selection of a length of at least one of an uplink control part and a downlink control part of a sub-frame, wherein a symbol length employed and number of symbols in the sub-frame define the granularity for the lengths, and number of symbols in the sub-frame and number of symbols available for each part of the sub-frame limit the at least one set of available lengths; selecting, in the network node, a length of at least one of the uplink control part and the downlink control part of the sub-frame, the length being selected amongst the at least one set of available lengths, the sub-frame comprising the uplink control part carrying at least one of uplink control information and an uplink reference signal and further comprising the downlink control part carrying at least one of downlink control information and a downlink reference signal, wherein the length of the least one of the uplink control part and the downlink control part is selected link direction-wise by assigning resources in the sub-frame for said control part first and allocating remaining resources for data, wherein the uplink control part comprises the uplink signalling information contained in the sub-frame and the downlink control part comprises the downlink signalling information contained in the sub-frame, and causing transmission of a message comprising at least one information element indicating the selected length of the at least one of uplink control part and downlink control part of the sub-frame.