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Subject: Issue 25 - form of seqAck when RMD has received no message
I’d like to propose an alternate resolution for issue 25. In the meeting yesterday, we discussed issue 25 and the
group expressed its opinion that they preferred a definite statement to be made
in this boundary case of no messages received yet. The remaining proposal being considered last night was to
send “Ack 0..0” for the case where no messages have been received. <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
<wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
<wsrm:AcknowledgementRange Upper="0" Lower="0"> </wsrm:SequenceAcknowledgement> My intellectual concerns with this approach are that we are
making an incorrect statement – we are acknowledging receipt of a message
[#0] that (a) we haven’t actually received, (b) doesn’t actually
exist, and (c) will never be sent My practical concerns with this approach are that I fear this
change may cause a large ripple effect on implementations. I suspect implementations will need to change to explicitly recognize
and exclude / ignore the dummy message #0 anywhere they use a sequence range (although
I haven’t actually checked into the details yet). Also changing the schema to say #0 is in the message number
range makes it harder to do effective validation of message content on the wire
(should you wish to do that) – specifically is Ack 0..10 valid or just
Ack 0..0? I believe we already have existing features of the RM spec that
can be used to solve this problem and make a definite but correct statement to
handle this boundary condition – We can assert “I’m still
waiting for you to send me the first message” – eg. “Nack 1” <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
<wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
<wsrm:Nack>1</wsrm:Nack> </wsrm:SequenceAcknowledgement> The advantages of this approach are:
So I propose the following resolution for Issue 25 Recommend that an RMD be
required to respond with a SequenceAcknowledgement element containing a Nack
child element with content “1” to signify that the first message has
not yet been received for a given Sequence. e.g. <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
<wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
<wsrm:Nack>1</wsrm:Nack> </wsrm:SequenceAcknowledgement> |
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