connection admission control to an atm network from a plurality of sources sharing a common virtual channel connection in which information packets are carried in cells is effected by determining whether that connection requires the transmission of a single packet per cell , partially filled cells containing more than one packet or fully filled cells . where a single packet is to be transmitted per cell , the bandwidth requirement is calculated via a first algorithm . where fully filled cells are to be transmitted , the bandwidth requirement is calculated via a second algorithm . where partially filled cells containing more than one packet are to be transmitted the bandwidth requirement is calculated via an interpolation between the two algorithms . this provides a more accurate measure of equivalent bandwidth and thus facilitates efficient use of network resources .