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

[Scott Burleigh]

At 11:51 AM 4/1/2004 +0100, Massimiliano.Ciccone at esa.int wrote:

>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).

Actually, Max, my point was exactly that the new Unacknowledged CFDP 
Extensions make this no longer true: in unacknowledged mode, the 
transaction now terminates on receipt of the EOF PDU only if file reception 
is complete.  If reception is incomplete then we instead start a Check 
timer, and the transaction terminates only upon expiration of that timer at 
a time when reception has completed (or the maximum number of Check 
timeouts has been reached).

Since it's now possible for reception of the EOF PDU in unacknowledged mode 
to *not* terminate the transaction (and thus not issue a 
Transaction-finished indication), it seems reasonable to me to let the 
local entity issue an optional EOF-received indication to make up for the 
loss of this potential signal to the application.

>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.

Because the only effect of this change would be to deliver an indication to 
the user application, I don't think we would need to constrain it as you 
propose.  The protocol is not affected in any way, and we can let the user 
application respond to the indication however it likes.

>    The EOF.Received Indication shall report the condition code of the EOF PDU

I think that's an excellent idea.

Scott