An apparatus to generate test traffic for testing a network. A scheduler may provide packet definition data for a sequence of packets, each packet associated with a respective flow control group. A channelized schedule FIFO (first-in first-out) queue may store the packet definition data. The channelized schedule FIFO queue may include multiple parallel channels, each channel dedicated to storing packet definition data associated with a corresponding flow control group. A plurality of non-channelized packet builder lanes may build packets in accordance with packet definition data read from the channelized schedule FIFO. A channelized output FIFO buffer may store packets built by the plurality of packet builder lanes. The channelized output FIFO buffer may include multiple parallel channels, each channel dedicated to storing packets associated with a corresponding flow control group. An output multiplexor may interleave packets from the channelized output FIFO buffer to form the test traffic.