Multiple endpoints per RM sequence scenarios

[Doug Davis <dug@us.ibm.com>]

Marc et al,
  I took a todo from the last conf
call to pull out the use-cases from the "Lack of support for multiple
endpoints per Sequence" issue I raied with Marc's proposal.  From
the note I send before [1], here is the key section:

------
There are lots of scenarios in which
a series of messages need to sent where the order must be preserved.  Clearly
one way to achieve this is to serialize the sending of the messages so
that message number N is not sent until message number N-1's response is
received.  However, this is not a very efficient model.  RM is
an obvious choice here.  By using RM a sending endpoint can parallelize
its sending of the messages and be assured that the other side will reorder
them appropriately.  Thus adding a firewall into the environment you
now have a series of anonymous clients all sending messages that need to
be in the same RM Sequence in order to achieve the desired results.  Saying
that the clients should not be anonymous in the first place is simply ignoring
the problem that many of our customers have. BTW, we have a requirement
for this in some notification systems, where we need to ensure that the
events we're sending are not processed out of order.  

 Looking at another use-case -
say there's an RMS is implemented as a gateway/proxy  - where all
messages leaving the environment heading for another destination are placed
into the same RM Sequence - because there's (as I've heard Chris describe
it) "one big pipe" between the two companies.  In this scenario
the gateway has no idea of the MEPs being used or the application semantics
involved - all it basically does is add the RM Sequence header to the messages.
 It then becomes up to each individual client (since its the only
one that knows the MEPs and application semantics) to request the responses
that may be expected.  Again, we need to be able to identify which
response goes to which client/MakeConnection request. 
------

But I think the entire note (if not
the entire thread) should be read  :-)

As with may use-cases there many ways
these could be supported however I'd like to see how these scenarios can
work using Marc's MC proposal and what assumptions would need to be made
about the implementation choices.  In particular:
- who is required to send the MakeConnection?
 Can the client do it or must it come from the gateway?
- if it is the client then how does
the right response get delivered to the right client since all the server
has is the anon wsa:To address?
- if it is the gateway then how does
the gateway know that a MC needs to be sent if it doesn't know the WSDL
or application semantics?
- if it is the gatewat then how does
the response get routed to the right client when the client may be doing
sync MEPs because it can't support hosting a server?
- and lets not forget about cases where
the gateway is an intermediary and the sockets are broken - w/o a server
on the client, if it doesn't send the MC then how does it work?
- how does the server group the messages
into the right sequence when all it has is the wsa:Anon URI for the wsa:To
value?  ie. how does it know which messages are going to the same
gateway or client is all it has is wsa:Anon to look at?  We need to
place the right message into the right sequence and one mechanism to do
this may be the destination endpoint (esp. in cases where the RM logic
isn't co-located with the application).

[1]  http://www.oasis-open.org/apps/org/workgroup/ws-rx/email/archives/200611/msg00047.html

thanks
-Doug
__________________________________________________
STSM | Web Services Architect | IBM Software Group
(919) 254-6905 | IBM T/L 444-6906 | dug@us.ibm.com