According to a first aspect, it is presented a method, performed by a network device, for determining a set of power state parameters at least partly defining when a wireless terminal is to be in an active state or a power saving state. The method comprises the steps of: obtaining at least one traffic characterization parameter; for each traffic flow, simulating a plurality of sets of power state parameters; obtaining at least one operational traffic characterization parameter; associating the operational traffic with a selected traffic flow; finding an applicable set of power state parameters by finding a set of power state parameters with a low cost, wherein the set of power state parameters are associated with the selected traffic flow; and sending the applicable set of power state parameters to the wireless terminal in operation. A corresponding network node, computer program and computer program product are also presented.