[T11.3] FCP-2 Error Recovery question

Hugh Curley hcurley at indra.com
Sat Jun 22 11:19:03 PDT 2002


INCITS T11.3 Mail Reflector
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I have been going over the ladder charts in annex C of FCP-2 rev 7a and
have a question on C17 and C19.  Both of these involve lost read data =
in
class 3: one the last frame of the data transfer sequence is lost, in
the other it is other that the last frame that is lost.
=20
Normal operation would be for the initiator to open the exchange by
sending a single frame sequence containing the command to the target,
the target returning the requested data in a single or multiple frame
sequence and then the target sending the status/response in a single
frame sequence.  As far as the target is concerned, it has done all and
done it properly, so it will set the "last sequence of the exchange" =
and
"last frame of the sequence" bits in the F_CNTL on the status/response
frame.  From the target's standpoint the exchange is completed.
=20
However, in these cases, C17 and C19, one of the data frames got lost =
in
the transport and never arrived at the Initiator (or arrived =
corrupted).
The target has no way of knowing this so goes on as above.  The
initiator discovers that a frame is missing, so after REC_TOV sends a
REC.  So far, all is OK.
=20
But I believe that when the target gets the REC asking for status on =
the
exchange, the target will see there is not open exchange with that =
S_ID,
D_ID and OX_ID because the target has completed that exchange and =
closed
it.  The target should therefore return an LS_REJ.  The notes on pages
C17 and C19 state that the target will send an ACC with Exchange Open.
=20
Why does the target see the exchange as Open?
What am I missing here?
=20
I could see that the target would not close the exchange until =
receiving
a CONF, but the charts make no mention of that optional facitlity being
used.
=20
Thank you for your help,
=20
=20
Hugh Curley
hcurley at indra.com =20
=20

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I have been going over the ladder = charts in annex C=20 of FCP-2 rev 7a and have a question on C17 and C19.  Both of these = involve=20 lost read data in class 3: one the last frame of the data transfer = sequence is=20 lost, in the other it is other that the last frame that is = lost.
  
 Normal operation would be for the = initiator to open=20 the exchange by sending a single frame sequence containing the command = to the=20 target, the target returning the requested data in a single or multiple = frame=20 sequence and then the target sending the status/response in a single = frame=20 sequence.  As far as the target is concerned, it has done all and = done it=20 properly, so it will set the "last sequence of the exchange" and "last = frame of=20 the sequence" bits in the F_CNTL on the status/response frame.  = >From the=20 target's standpoint the exchange is completed.
  
 However, in these cases, C17 and C19, = one of the=20 data frames got lost in the transport and never arrived at the = Initiator (or=20 arrived corrupted).  The target has no way of knowing this so goes = on as=20 above.  The initiator discovers that a frame is missing, so after = REC_TOV=20 sends a REC.  So far, all is OK.
  
 But I believe that when the target = gets the REC=20 asking for status on the exchange, the target will see there is not = open=20 exchange with that S_ID, D_ID and OX_ID because the target has = completed that=20 exchange and closed it.  The target should therefore return an=20 LS_REJ.  The notes on pages C17 and C19 state that the target will = send an=20 ACC with Exchange Open.
  
 Why does the target see the exchange = as=20 Open?
 What am I missing here?
  
 I could see that the target would not = close the=20 exchange until receiving a CONF, but the charts make no mention of that = optional=20 facitlity being used.
  
 Thank you for your help,
  
  
 Hugh Curley
 hcurley at indra.com
  


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