If true only the reliable stream is transmitted

Number of fragments to use.
the engine by default uses only 4 fragments (depends on net_maxfragments & raising it increases the number of fragments)
You can use up to 7 fragments at once as the engine doesn't support more.

Each CNetChannel has 8 sub channels for networking, on every transmit it uses a single sub channel and sends data.
The used sub channel is marked as used and the server waits until the channel sends a signal that the sub channel data was received
This argument causes all sub channels to be marked as free instantly after this transmit, making networking possibly unreliable but allowing for far greater speeds.