In one embodiment, a gateway between a variable delay network and a constant delay network receives over the variable delay network a plurality of data streams to be multiplexed over a modulated channel extending through the constant delay network. A first processing component of the gateway generates command-packet-descriptors corresponding to content packets included in the received data streams. A second processing component of the gateway uses transmit time indications included in the command-packet-descriptors to schedule transmission of modulated packets representing the received data streams over the modulated channel.