Apparatuses, methods, and systems are disclosed for scheduling of transmission time intervals. One apparatus includes a processor that determines a first semi-persistent scheduling resource assignment indicating a first set of resources including a first multiple time domain resources. Each time domain resource of the first multiple time domain resources has a first transmission time interval length. The processor also determines a second semi-persistent scheduling resource assignment indicating a second set of resources including a second multiple time domain resources. Each time domain resource of the second multiple time domain resources has a second transmission time interval length, and the first transmission time interval length is different from the second transmission time interval length. The apparatus includes a transmitter that transmits the first semi-persistent scheduling resource assignment using a first semi-persistent scheduling radio network identifier, and transmits the second semi-persistent scheduling resource assignment using a second semi-persistent scheduling radio network identifier.