iSCSI initiators and targets communicate with messages known
as “iSCSI Protocol Data Units”. An iSCSI PDU has
a Header and an optional Data Section.
iSCSI PDUs are transported in the TCP Segment Data Area of
Ethernet Frames. The size of an iSCSI PDU is not dictated by the
capacity of the TCP segment data area and an iSCSI PDU does not
need to begin at a specific offset within a TCP segment data area.
An iSCSI PDU can span multiple TCP segment data areas, or several
iSCSI PDUs can be contained in a single TCP segment data area.
