The three basic SAN-over-WAN protocols in widespread use on IP networks are based on the SCSI and Fibre Channel SAN protocols and depend on TCP:
iSCSI (Internet SCSI) encapsulates the standard SCSI-3 device interface commands in a TCP/IP data flow for transport over the WAN.
FCIP (Fibre Channel over TCP/IP) encapsulates standard Fibre Channel packets in a TCP/IP data flow. Alternatives can encapsulate Fibre Channel over ATM or other link transports.
Waiting for Acknowledgment
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iFCP (Internet Fibre Channel Protocol) intercepts Fibre Channel packets and spoofs them, replacing them with TCP sessions for transport across IP.