Described embodiments include a system that includes a network interface and a processor. The network interface is configured to receive, at a first time, a packet transmitted from a source communication terminal over a communication network en route to a target communication terminal, before the packet passes through a particular portion of the communication network, and to receive the packet at a second time, after the packet has passed through the particular portion of the communication network. The processor is configured to delay the packet, subsequently to the packet being received at the second time, by a delay duration that is a decreasing function of a duration between the first time and the second time, and to send the delayed packet, subsequently, via the network interface, en route to the target communication terminal. Other embodiments are also described.