[Moims-sc] Updated MO Packet Distribution Service Presentation

roger.rocketbrain at btinternet.com roger.rocketbrain at btinternet.com
Fri Jul 1 10:51:37 UTC 2022

Dear All,
In accordance with my Action from the last telecon, I have updated the Draft
MO Packet Distribution Service presentation, to address the points raised -
please see attached.
I hope I have captured the issues as agreed.
I have made one additional observation in the case we decide to support
packet retrieval for a time range:  if the Get operation is Progress pattern
rather than PubSub, then the filtering must be done by the Provider rather
than a generic Broker.  From the standard specification viewpoint this is
simpler, but it may not be for implementation.  
An alternative approach could be to use the concept of a "Replay" session -
use the same PubSub model as for the nominal streamed case, but in the
context of a Replay session rather than the "Live" stream.  Filtering would
be done by the Broker as for the nominal case.  Additional operations would
then be needed to control the Replay - create session, specify the time
period (and possibly replay speed), start, pause and stop.  This could be
powerful, as it could support a number of additional use cases:
*	Interaction with a Simulator
*	Action Replay rather than just bulk Retrieval (but if speed is "as
fast as possible" it supports the latter)
*	The Replay concept could be extended to cover other object types
(Parameters, Actions, Alerts) without requiring additional operations to be
specified for them.
*	Coordinated Replay from History for multiple users (and potentially
across multiple object types)
*	Stream control operations/options could be covered by capability
sets to allow for minimal implementations (e.g. only one type of object;
only one replay speed; no facility to pause/resume)
*	Replay control could be defined in a separate book, enabling us to
keep the M&C update needed to include Packet to a minimum.
However, the concept of Session has been removed from the MAL header in V2 -
there would need to be some way of identifying the session in the PubSub
messages - both on publishing and subscribing.
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