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    RE: iSCSI: SNACK wording clarification



    Hi everyone,
    
    I just went across the Sequence Errors section in the iSCSI I-D yesterday.
    Since I am new to the group, please accept my apology if the following
    questions have been already asked.
    
    "6.3 Sequence Errors
    
       When an initiator receives an iSCSI data PDU with an out-of-order
       DataSN or a SCSI command response PDU with an ExpDataSN implying
       missing data PDUs it MAY request the missing data PDUs through a data
       SNACK PDU or handle this case as a connection failure.  In its turn,
       the target MUST either reject the SNACK with a Reject PDU with a
       reason-code of Data-SNACK-Reject or resend the data PDU.
    
       When an initiator receives an iSCSI status PDU with an out-of-order
       StatSN implying missing responses, it MUST either request the missing
       response PDUs through a status SNACK or handle this case as a
       connection failure.  The target MUST reissue the missing responses.
       As a side effect of receiving the missing responses, the initiator
       may discover missing data PDUs. The initiator MUST NOT acknowledge
       (either explicitly through ExpStatSN or implicitly through a status
       SNACK) the received responses until it has completed receiving all
       the data PDUs of a SCSI command. "
    
    My questions are:
    
    1.  In the iSCSI I-D: "iSCSI uses Command and Status numbering schemes and a
    Data sequencing scheme.  It supports ordered command delivery within a
    session.  All commands (initiator-to-target) are numbered".  As I understand
    it means that the iSCSI initiator won't deliver the next PDU until it
    receives the acknowledgement from the target (through StatSN, ExpCmdSN).
    Also, the target executes the PDU with sequence number it expects.  It won't
    execute the out-ot-order PDU.  Am I understanding it right?
    
    2.  From the section 6.3 "Sequence Errors", I have the impression that iSCSI
    can send multiple PDUs without waiting for the acknowledgement.  If it's
    true, then it conflicts with the question 1?  If it's true, then does iSCSI
    need a timer to time every PDU it deliver?  The iSCSI I-D doesn't mention
    about the timer at all.
    
    Thank you,
    
    Trang Nguyen
    
    


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Last updated: Tue Sep 04 01:04:17 2001
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