NEW ISSUE: Duplicate detection of wsrm:CreateSequence messages

[Anish Karmarkar <Anish.Karmarkar@oracle.com>]

Title:
Duplicate detection of wsrm:CreateSequence messages

Description:
wsrm:CreateSequence messages can be duplicated, delayed a/o resent by 
the RMS (for lack of response or lost CreateSequenceResponse). Therefore 
it is possible that one RMS create Sequence request message may result 
in creation of multiple (spurious) Sequences at the RMD. Each Sequence 
at an RMD may require resource reservation resulting in excessive 
resource utilization or unnecessary refusal from RMD to create new 
(legitimate) Sequences.

Justification:
WSRM spec is created to reliably deliver messages in an unreliable 
environment, where message may be lost, duplicated, delayed or received 
out-of-order. This unreliable environment applies not only to payload 
message but also to protocol signal messages such as 
wsrm:CreateSequence/wsrm:CreateSequenceResponse messages.

Typically on receiving a wsrm:CreateSequence message, the RMD reserves 
resources for the sequence (when it does not generate a fault) and 
responds with a wsrm:CreateSequenceResponse.

It is possible that the underlying network duplicates/delays/loses the 
wsrm:CreateSequence message OR it is possible that the RMS resends 
wsrm:CreateSequence message for a lack of response (or because the 
wsrm:CreateSequenceResponse message was delayed or lost). In such a 
scenario the RMD may end up unnecessarily reserving resources (till the 
expiration time/inactivity Timeout of the Sequence) for Sequences that 
were never requested. This may result excessive resource utilization or 
refusal of legitimate Sequence request because of spurious requests 
taking up all the RMS resources.

Target: core

Type: design

Proposal:
Require that the RMS include the wsrm:Identifier in the 
wsrm:CreateSequence request. I.e RMS decides on the identifier for the 
Sequence rather than the RMD. RMD merely echos the wsrm:Identifier in 
the wsrm:CreateSequenceResponse that was present in the 
wsrm:CreateSequence message (or faults).

If it is essential that the RMD generate the wsrm:Identifier for the 
Sequence (and I would like to understand why that is so -- I have some 
idea of why that may be the case, but not sure if that is the reason why 
it is so), then a different approach will have to be taken. Something 
along the lines of:
-- require the RMS to specify a suggested wsrm:Identifier in the CS and 
allow the RMD to ok that or override it in the CSR message.

Related issues: none