HP-UX iSCSI Software Initiator Support Guide, HP-UX 11i v1 and 11i v2, July 2005

Chapter 1

iSCSI Overview

The iSCSI PDU

iSCSI initiators and targets communicate with messages known as “iSCSI Protocol Data Units”. An iSCSI

PDU has a Header and an optional Data Section.

Figure 1-2 iSCSI Protocol Data Unit (PDU)

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.

Figure 1-3 TCP Segment Data Area of an Ethernet Frame