Status: Accepted Owner: ---- Labels: Type-Review Priority-Medium FoundInVersion-1.0 FixedInVersion-1.1 New issue 55 by thost...@gmail.com: correlationId is unneeded and complicates implementation significantly http://code.google.com/p/ogf-nsi-project/issues/detail?id=55 Description of Issue: The correlationId attribute in the WSDL messages is unneeded. Furthermore it requires correct implementations to persistently keep track of the correlationsIds of active requests. Discussion of Issue: The WSDL adds a correlationId to track the correspondence between a request and the subsequent update for the status. However this correspondence is unneeded as the request already contains information about the connection in question. However having the correlationId requires both the requester and provider to keep a persistent (as in on-disk) record of currently active requests, in order to be crash and restart safe, i.e., the service must be able to respond to requests that came before it crashed/restarted. The correlationId also means that state updates are not idempotent as the client can only receive a request (state update) once. However it cannot be guaranties that a message with a state update will only be send once due to the coordination of message dispatching and updating this information persistently, where there will always be a window which can lead to inconsistency, where the message must be retransmitted. Having to keep track of requests in this way, is called a state-full protocol (note that this does not mean a non state-full protocol doesn't have any state), and is usually considered a bad idea do implementation complexity and poor scalability in high-performance systems (arguably this is not what we have though), as it makes load balancing and redundancy significantly more tricky. Furthermore it must be remembered that not all requests will have a callback. E.g., a provision before start time (i.e., auto-provision) followed by subsequent terminate request, will result in a callback for terminate, but not for the provision request. Here the client must then clear all pending correlationIds, complicating the implementation (the client side issues are simple though). All this is further complicated by the fact that we haven't established if it is the provider or requester which is responsible for ensuring that correct connection state is updated. Resolution of Issue: Remove correlationId from the WSDL. This will make the state update messages (reserveConfirmed, etc.) idempotent, meaning they can be repeated. The requester will then update any state references about the remote connection to fit with the last received message (this also has problems, but none that doesn't exist in the current protocol).