[Css-csts] NotifyInvocation before TransferDataInvocation in Buffered Data Delivery procedure

[John Pietras]

The Behavior section for the Buffered Data Delivery procedure specifies
that following the START, the first thing to be sent is a
TransferDataInvocation. Specifically:
"4.4.2.1.2	After a successful START operation the provider shall
transfer the data by means of invoking the TRANSFER-DATA operation,
conforming to the selection criteria and as the data become available
from the production."
and
"4.4.2.3.3	After a successful START operation:
4.4.2.3.3.1	The transfer shall begin with the most recently
generated data following the start-generation-time specified in the
START operation. ..."

However, this is not represented in the state table for the Buffered
Data Delivery procedure. The state table indicates that once the
procedure is in the active state, a sync notify for 'production status
change' or 'any event' is inserted into the transfer buffer without
regard to whether a TransferDataInvocation was sent first.

What is the desired behavior - always require that the first thing sent
is a TransferDataInvocation, or allow a NotifyInvocation to be the first
thing in the buffer following the START if the corresponding event
occurs before "data" is available?

Please note that for the Tracking Data CSTS, the first thing sent
following the START *must* be a NotifyInvocation bearing the initial TDM
metadata, in order to conform to the TDM format requirements. If the
behavior of the standard Buffered Data Delivery procedure mandates that
the first record be a TransferDataInvocation, then the behavior of the
Buffered Tracking Data Message Delivery procedure will have to reverse
that requirement in its behavior. 

On the other hand, if the behavior of the standard Buffered Data
Delivery procedure allows the first record after START to be a
TransferDataInvocation or a NotifyInvocation, then the behavior of the
Buffered Tracking Data Message Delivery procedure will refine the
behavior to require that the first record be a NotifyInvocation bearing
TDM Metadata. 

It is my opinion that the standard Buffered Data Delivery procedure
should not mandate that the first record be a TransferDataInvocation, as
represented by the state table. It inhibits multiple legitimate uses of
the procedure in which the first thing of interest may not be a
TransferDataInvocation. For example, consider an instance of an "RCF"
service in which the selected VC carries data that occurs infrequently,
say, once per minute. If the production status changes after the service
instance has STARTed but before the first frame of the selected VC has
been received, presumably the service instance should still notify the
user of the new production status.

If a specific service requires that a TransferDataInvocation be sent
first, the behavior of its derived procedure can be refined to mandate
that.

Of course, if we agree that the state table is correct and there should
be no prohibition of an initial NotifyInvocation, paragraphs 4.4.2.1.2
and 4.4.2.3.3.1 should be clarified.

Best regards,
John

John Pietras
Global Science & Technology, Inc. (GST)
7855 Walker Drive
Suite 200
Greenbelt, Maryland, USA
20770-3239
Direct:   +1-240-542-1155
GST Main: +1-301-474-9696
Fax:      +1-301-474-5970