[evla-sw-discuss] VCI and Message IDs

[Kevin Ryan]

Hello gang,

I would like to comment on Sonja's VCI document about the 'Message  
ID' in which I disagree with its need or for its possible benefits  
for 'debugging and troubleshooting'.  Its inclusion in the VCI  
document suggests the use of UDP type communication between the EVLA  
and WIDAR and I truly hope that is not the case.

And I also truly hope that the use of Message IDs does not penetrate  
past the VCI.  WIDAR's internal communication infrastructure is based  
on the fact that there will be no blind requests - every single  
request _will_ be acknowledged.  Every request for a status or for a  
configuration change will not be complete until the server has  
acknowledged it (or the TCP or HTTP layers indicate a malfunction).

If the VCI-to-EVLA infrastructure maintains that philosophy, then the  
two use-cases for Message-IDs in the VCI document become moot:
  - "A VCI message generated as a direct reply to a received VCI  
message should include the Message ID."
    Since the request and response is a socket connection between the  
requester and the responder, the response con only be for that  
particular request.

  - "A log/alarm generated to report erroneous or unexpected message  
or inability to act as specified ... should include [the] Message ID"
    Any request that is 'erroneous or unexpected' will be immediately  
known to the requester via the response.  If, later on, there is an  
'inability to act' then that is a different matter that has nothing  
to do with the ID of original request and therefore does not need to  
be linked to it.

Message IDs are a necessary complication for the implementor of UDP- 
based communications but TCP/HTTP encapsulates that functionality so  
we don't have to be bothered with it.

I therefore make two recommendations:
  1) Remove the need for Message IDs (don't attempt a control system  
based on communications 'in the blind'),
  2) Remove Message IDs from the VCI document.

Regards,

Kevin