Flow control in a virtualized communication network

A device for determining oversubscription of a first virtualized network function (70) in order to enable flow control in the virtualization of at least one node in a communication network comprises a first virtualized network function (70) having packet handling resources comprising at least one queue (108, 112, 114, 120) and being a downstream network function located downstream from at least one second upstream network function in a packet flow between the network functions. The device comprises flow control functionality (79) set to monitor at least one queue (108, 112, 114, 120), determine if the first virtualized network function (70) is oversubscribed based on the monitoring, and generate, in case the first virtualized network function is determined to be oversubscribed, an instruction for at least one upstream network function to change its transmission rate to the first virtualized network function (70) in order to reduce the oversubscription.