Refer to Figure 11-2 on page 212. When a QP is created, one of the values that must be set is the SQ Logic's Start PSN value. This is the PSN that will be inserted into the first request packet generated by the SQ Logic. It may be any value in the range from 000000h through FFFFFFh.
The specification stresses that a value should be selected that:
“minimizes the chance that a packet from a previous connection could fall within the valid PSN window.”
The specification ...