3.1.5.3.2.1 Source Packet
A Source Packet is generated as specified in section 3.1.5.1.4. A Source Packet is sent only if one of the following occurs:
A datagram has been marked as a lost datagram (section 3.1.1.4.1), and it has not been retransmitted.
There is space in the receiver-advertised window for this datagram and the Congestion Control logic permits transmission of a datagram.