[Sis-uce] Suggestion for CFDP (add EOF-Received Indication)

[Massimiliano.Ciccone at esa.int]

Dear Tim and Scott,
I believe that what you are proposing here make sense, but only if we are in
presence of ACKNOWLEDGED transactions. This because, in UNacknowledged mode,
transaction always TERMINATE on receipt of EOF PDU anyway (issuing a
transaction.finished indication). Moreover, it would not make sense to use
the EOF.Received indication as explained in Tim's example if the link was
only one-way all the time.
If we are going to use an EOF.Received indication for triggering suspension
of ACKNOWLEDGED transaction, then there are some provision to make:
   The Transaction must be in "Deferred Nack" mode, to avoid the receiving
   side sending NACK PDUs before reception of EOF.
   The EOF.Received Indication shall report the condition code of the EOF PDU

Looking forward to your comments

Max



                                                                                                                                                        
                      Scott Burleigh                                                                                                                    
                      <Scott.Burleigh at jpl.na         To:      sis-uce at mailman.ccsds.org                                                                 
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                      31/03/2004 21:02                                                                                                                  
                                                                                                                                                        
                                                                                                                                                        




At 02:14 PM 3/31/2004 -0500, Timothy Ray wrote:
      Hello all,

      I suggest that we:
         1) Add an "EOF-Received" Indication to CFDP
         2) Add an MIB parameter to enable/disable it
             ("EOF-Received.indication required?" "yes or no")
My rationale:
   This Indication is useful for some mission scenarios; CFDP has the
information, why not make it available to the user?

Example of usefulness:
   The Global Precipitation Measurement mission is using CFDP.  Their link is
one-way (telemetry only) most of the time.  They blast files down during the
one-way link, and then enable the feedback loop during the two-way link.  The
EOF-Received Indication allows the Receiver to suspend each transaction upon
receipt of an EOF PDU.  All transactions are then resumed at the start of the
two-way link.  (A similar mechanism on-board uses the EOF-Sent Indication)


Scott wrote:
The relevance of this tweak to the Unacknowledged CFDP Extensions may not be
obvious, but I think it is real.  By turning off Notice of Completion
issuance on receipt of EOF in Unacknowledged mode when the file is not
completely received, UCE disables delivery of the Finished indication under
these conditions.  It is possible that some CFDP implementations might count
on that indication to signal EOF arrival in Unacknowledged mode (regardless
of file delivery completeness), for purposes similar to those Tim describes;
UCE would break those implementations.  By adding an optional EOF-Received
indication we could provide a replacement source for this information without
working too hard.

I definitely DO NOT want to open the door to casual reconsideration of CFDP
specification elements in general.  But I think the UCE revisions do arguably
motivate Tim's proposed mod, and I think the impact of the change would be
modest.  Let's discuss on this list and at the UCE working group meeting in
Montreal.

Scott_______________________________________________
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