A method and apparatus are disclosed for assessing the available resources in a network and using the assessment for admission control. A VoIP call can be established with a device only if the network has sufficient resources to accommodate the call or it is possible to make such resources available by curtailing ongoing data connections. A network utilization characteristic (NUC) provides a measure of network capacity. The network utilization characteristic of a flow is the fraction of time the network is busy transmitting data for that flow. The sum of the network utilization characteristics of all flows yields the fraction of time the network is busy transmitting data. The difference between one and the sum of all flows indicates the time that the network is idle in the measured time interval. A new flow can be accommodated if the NUC of the new flow is smaller than this difference value.