A network node for reserving resources for data flows in a communication network. The node detects a request for resource reservation for a new data flow and computes an admission test count based on descriptors of the new data flow and reservation counts, which represent reservation functions of descriptors of previously admitted data flows and which specify resources of the admitted data flows. The new data flow is admitted if the admission test count is smaller than a maximum allowable count. The reservation counts are then updated based on the descriptors of the new data flow. A plurality of admission formulas may thus be used to maintain aggregated reservation counts for data flows, the number of counts being independent from the number of flows.