An apparatus (301; 302; 303) for use in a packet-based communication system, the apparatus comprising an input (30, 32) and an output, and being configured to: receive a stream (1; 1') of data packets (5, 6) at said input, wherein the stream of data packets has an inter-packet spacing defined as the duration of the gaps between two consecutively transmitted data packets of said stream, and wherein each of the data packets is no longer than a common maximum data-packet length; store the received data packets and information representing the inter-packet spacing in a buffer; and i) generate or receive gap bytes between successive data packets based on said information representing the inter-packet spacing and place data packets stored in said buffer with said gap bytes placed between them, except for a constant amount, into a respective container (2; 2') of a sequence of containers; or ii) when the input is silent between data packets, time each gap between successive data packets and place data packets stored in said buffer into a respective container (2; 2') of a sequence of containers, leaving corresponding gaps between the successive data packets in the respective container, except for a constant amount, wherein each container occupies a respective contiguous block of time whose start and end is identifiable to a receiving apparatus, and, if the container then contains an incomplete data packet, additionally schedule the remainder of the incomplete data packet, from the buffer, into the container; and send, in cycles, from said output, a predetermined number of containers from said sequence of containers in each cycle, wherein the positions of the data packets within the containers depend on the received inter-packet spacing, and wherein the constant amount is equal to or greater than the common maximum data-packet length. receive a stream (1; 1') of data packets (5, 6) at said input, wherein the stream of data packets has an inter-packet spacing defined as the duration of the gaps between two consecutively transmitted data packets of said stream, and wherein each of the data packets is no longer than a common maximum data-packet length; store the received data packets and information representing the inter-packet spacing in a buffer; and i) generate or receive gap bytes between successive data packets based on said information representing the inter-packet spacing and place data packets stored in said buffer with said gap bytes placed between them, except for a constant amount, into a respective container (2; 2') of a sequence of containers; or ii) when the input is silent between data packets, time each gap between successive data packets and place data packets stored in said buffer into a respective container (2; 2') of a sequence of containers, leaving corresponding gaps between the successive data packets in the respective container, except for a constant amount, i) generate or receive gap bytes between successive data packets based on said information representing the inter-packet spacing and place data packets stored in said buffer with said gap bytes placed between them, except for a constant amount, into a respective container (2; 2') of a sequence of containers; or ii) when the input is silent between data packets, time each gap between successive data packets and place data packets stored in said buffer into a respective container (2; 2') of a sequence of containers, leaving corresponding gaps between the successive data packets in the respective container, except for a constant amount, wherein each container occupies a respective contiguous block of time whose start and end is identifiable to a receiving apparatus, and, if the container then contains an incomplete data packet, additionally schedule the remainder of the incomplete data packet, from the buffer, into the container; and send, in cycles, from said output, a predetermined number of containers from said sequence of containers in each cycle, wherein the positions of the data packets within the containers depend on the received inter-packet spacing, and wherein the constant amount is equal to or greater than the common maximum data-packet length. wherein the positions of the data packets within the containers depend on the received inter-packet spacing, and wherein the constant amount is equal to or greater than the common maximum data-packet length.