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

Chapter 1

iSCSI Overview

iSCSI Session and TCP Connections

In an iSCSI session, communication between an initiator and a target occurs over one or more TCP

connections. The TCP connections carry control messages, data digests, SCSI commands, parameters, and

data, all encapsulated in iSCSI Protocol Data Units (iSCSI PDUs).

The TCP connections that link an initiator with a target, forming an iSCSI session, are comparable to a SCSI

I_T nexus.

An initiator sees one “target image” across all of the connections in a session. A target also sees one “initiator

image” across all of the connections in a session.

iSCSI defines two types of sessions:

• Normal Operational Session - a session in which SCSI commands, data and responses can be

transferred between an iSCSI initiator and an iSCSI target.

• Discovery Session - a session only opened for target discovery.

Figure 1-5 An iSCSI Session