Subject: [Ips] cmdSN related questions

From: "T.Krishnanand" <[email-masked]>
Date: Wed, 23 Nov 2005 17:57:34 +0530

Hi,

Assuming ERL 0,

1) Can someone explain clearly what the following means:

"The CmdSN carried by immediate commands may lie outside the ExpCmdSN
to MaxCmdSN range. For example, if the initiator has previously sent a
non-immediate command carrying the CmdSN equal to MaxCmdSN, the target
window is closed."

In the above case, cmd window closed, say expCmdSN = 11 and maxCmdSN =
10, does it mean that the cmdSN of the next cmd from initiator would
be 11 and it is outside the valid-cmdSN window (maCmdSN+1 - expCmdSN).

2) Is there any case when a target MUST accept an immediate cmd
(non-taskmgmt) pdu with cmdSN LESS THAN target's expCmdSN ? If YES
what is the case.

3) Is there any case when a target MUST accept an immediate cmd
(taskmgmt) pdu with cmdSN LESS THAN target's expCmdSN ? Im confused
becoz..

The RFC says that TM cmds like ABORT-TASK-SET etc use cmdSN as the
marker for scope of cmds affected by this task mgmt cmd. I assumed
that in such cases the cmdSN carried by the TM cmd can be LESS THAN
target's expCmdSN. But RFC also says ABORT-TASK-SET aborts ALL
outstanding cmds for the session which implies the cmdSN for
ABORT-TASK-SET cmd must be the current cmdSN value at the initiator
end which in turn implies that the cmdSN CANNOT be LESS THAN target's
expCmdSN.

thanks,
tkrishna

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From: [email-masked]
Date: Wed, 23 Nov 2005 10:23:15 -0500

1)  Yes the immediate command sent after the window closes will carry the
CmdSN of 11.  I don't think you can ever get an immediate command that is
greater than MaxCmdSN+1.

2)  If you have multiple connections per session then you have a race
condition that can allow commands to arrive out of order.  If an initiator
sent an immediate command through connection 1, and some non immediate
commands through connection 2 it is possible that the non immediate commands
will arrive at the the target fist.  In this case the immediate command will
arrive with a CmdSN lower than the targets expCmdSN. 

3)  Same answer as 2.   However if you are only supporting one connection
you shouldn't have a problem.

- Bill

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
T.Krishnanand
Sent: Wednesday, November 23, 2005 7:28 AM
To: [email-masked]
Subject: [Ips] cmdSN related questions

Hi,

Assuming ERL 0,

thanks,
tkrishna