iSCSI Protocol Architecture
The iSCSI Protocol
The iSCSI Protocol
Application
Application Layer
SCSI Class Driver
SCSI Layer
iSCSI Protocol
Services
iSCSI Layer
Transport (TCP)
Security (IPSec)
Optional
TCP/IP Layer
Network (IP)
Physical Layer
Data Link
(Ethernet or other)
The iSCSI protocol is a mapping of the Serial SCSI-3 protocol over the TCP
protocol. The iSCSI protocol model consists of the following:
The Application Layer initiates and responds to I/O transactions.
The SCSI Layer builds and receives SCSI CDBs (Command Descriptor
Blocks) and relays and receives the CDBs to/from the iSCSI layer.
The iSCSI Layer builds and receives iSCSI Protocol Data Units (PDUs)
and relays and receives the PDUs to/from the TCP/IP layer.
The TCP/IP Layer encapsulates PDUs in TCP segments using one or
more TCP connections that form an initiator-target “session”, and
encapsulates TCP segments into IP packets. IPsec is an optional
component of this layer.
The Physical Layer transmits and receives IP packets, typically using
Ethernet. WAN protocols like Point-to-Point Protocol (PPP) and Packet-
over-SONET/SDH (PoS) are also supported. The iSCSI standard does
not mandate any particular physical-layer transport.