FC-2 Features
62 SL500: Interface Reference Manual • July 2008 Revision: F • 96122
Exchange Management
Exchange (X) management is the overall control of operations over the Fibre
Channel interface between the originator and responder. Refer to the FC–PH
documents for rules and guidelines pertaining to Class 2 operation.
Note: For FCP, an exchange is a single SCSI command.
There are two fields in the frame header dealing with exchanges:
■ OX_ID = Exchange originator
■ RX_ID = Exchange responder
Exchange Originator
The exchange originator assigns a unique OX_ID to the exchange for the
transmission of in-order delivery of frames and assumes the frames are processed
in the order received. The exchange is open from the time the first frame is sent
until one of the following occurs:
■ Timeout
■ The exchange is aborted (ABTS or ABTX)
■ An end-of-frame (EOF) delimiter is sent with the last sequence bit set
■ A Logout (LOGO) is sent to or received from the Exchange responder
■ A Link Service Command Reject (LS_RJT) is sent in response to an ADISC or
PDISC during target discovery
■ A PLOGI is sent to the Exchange responder
Exchange Responder
The exchange responders assign unique RX_ID values or use the value of “FFFF.”
The exchange responder considers an exchange open from the time it receives the
first frame of the first information unit until one of the following occurs:
■ The last frame of the last information unit is sent with the last sequence bit set
■ The exchange is aborted (ABTS)
■ A Logout (LOGO) is sent to, or received from, the Exchange originator
■ An LS_RJT is sent in response to an ADISC or PDISC during target discovery
■ A PLOGI is received
TABLE 5-14 Exchange Content Header
Word Byte 0 Byte 1 Byte 2 Byte 3
0 R_CTL Destination_ID
1CS_CTL Source_ID
2Type F_CTL
3SEQ_ID DF_CTL SEQ_CNT
4 OX_ID RX_ID
5 Parameter
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