Techniques are disclosed for controlling the transmission of packets over a communication link in a network. The invention in accordance with one aspect thereof determines a number of packet transmission connections supportable for a given buffer size in a node of the network while maintaining one or more specified quality of service requirements for packet transmission. This determination in the case of homogeneous input sources utilizes a combined approximation of a maximum number of supportable connections for a range of buffer sizes, the combined approximation being generated as a combination of a first approximation for small buffer sizes and a second approximation for large buffer sizes. The invention can also be used to determine an optimal operating point on a buffer-capacity tradeoff curve for each of a number of different types of heterogenous input sources. Data packets from multiple input sources may be admitted to the node of the network, or otherwise processed within the node, based at least in part on the determined number of supportable connections.