One note - keep a clear mental separation of the XSD and the WSDL. The XSD represents the generic modelling of the NSI protocol independent of transport. The WSDL attempts to provide an instance of reliable transport for implementation prototyping.
On 2011-07-13, at 7:16 AM, Henrik Thostrup Jensen wrote:
Hi everyone
(I'm the NORDUnet developer creating the OpenNSA NSI implementation).
(Also, please ignore a potential double post due to wrong sender email)
I have some feedback/changes/wishes/questions for the WS-rendering of the
NSI protocol.
1. Odd request/reply structure.
The request/reply structure is somewhat odd. It seems that for every
request there is an message to imply that the message itself has been
received as well as the actual response, which also has a response. I.e.,
the interaction will look like this for a reservation (AFAICT)
A -> B: reserveRequest
A <- B: reserveResponse
A <- B: reserveConfirmed
A -> B: reserveConfirmedResponse
This means that 4 messages are exchanged, when 2 would be enough. This is
silly in my opinon, and only adds complexity to the implementation without
adding any value. Also, at some point in time the reserveResponse and
reserveConfirmed will get reordered as they don't have any ordering
between them, meaning the requester will have to understand that case. It
also seems to against the spec, which defines the primitives
reserveRequest, reserveConfirmed, and reserveFailed.
You are correct. Four messages will be exchanged per request/confirmed/failed interaction, however, these are only two operations from an XSD perspective. Remember to separate the NSI operations from the WSDL transport. The reservationRequest is carried across in a SOAP POST operation, it gets accepted on the remote NSA, and the remote NSA returns either reservationResponse or SOAP fault in the POST result. We need this reservationResponse to acknowledge the remote NSA has received the reservationRequest otherwise we will keep trying to send.
This request/acknowledgement model was needed to address the requirement that many of the NSI operation are long duration, taking seconds to minutes, to days for the confirm/failed response to return. For any reasonable error handling to be achieved we needed to introduce an acknowledgement of some type. The GenericResponseType message returned as the acknowledgement is an empty sequence, but at least provides a positive indication that the request was received (hmmm... I had transactionId in there at one point - I might put it back in).
Can I get a confirm back before the the ack for the request? Yes you could depending on the remote NSA design but this is not an issue since the transactionId models the request/confirm/failed interaction, so I can easily handle this in software logic.
If I had been doing the NSI protocol from scratch as an web service it would be quite different. Doing the generic abstract protocol first is always tough for implementation given you end up with the worse of both worlds :-)
2. Moving pathObject out of ServiceParameters
I would very much like to move pathObject out of serviceParameters and
into the top-level attributes. As a reservation is created the pathObject
send around changes, where as the rest of the ServiceParameters does not.
This also reflects itself in data structures where this becomes somewhat
backwards to keep track of the path in aggregate connections. It is of
course completely possible to keep the current structure, but it would
simplify the implementation to move the path out of the service
parameters.
We placed the path object into the service parameters is part of the specific service attributes used to guide the service request, and therefore, seemed relevant with other service specific attributes. I don't specifically understand your concerns with respect to implementation, but you are probably further along than I am. I think we will need to get additional input from the team.
Also: Rename pathObject to path everywhere. We do not put the object
suffix on other things either.
Yes, I agree with this.
Also(2): Rename OrderedStpListType to StpListType in spec. and protocol. A
list is by definition ordered, otherwise it would be called a multiset or
bag.
Yes.
3. Protocol service parameters differ spec service parameters
In the spec. schedule is in service parameters, in the WS protocol it is
in the ReservationRequestType. I don't have any strong opions on where it
should be, but I think it should be consistent.
Somewhat similarly the spec. has guarenteed and preferred under
serviceAttrs (which is under ServiceParameters). In the WS protocol
guaranteed and preferred are directly under ServiceParameters. Again I
don't have any strong opions on what is correct, but I think it should be
consistent.
I believe we made a change that was probably not captured in the document.
4. The transactionId
The transactionId is not mentioned in the spec., but is used to denote
session due to SOAPs lack of it. Could we call it something less
misleading? It has nothing to do with transactions. E.g., sessionId,
requestId (i prefer the latter as a session could technically consist of
several requests).
The transactionId is for an NSA to correlate a request to a confirm/failed. If you get a confirm or failed back before the ack to the request then you can still correlated it based in transactionId. The transactionId does not represent a session. Only a single message exchange between a pair of NSA. I have baounce
5. Inconsistent path description
The spec. introduces the notion of a service demarcation point as a pair
of connected STPs. Could we introduce this type (essentially a
tuple/struct/complextype with two STPs), and use it for describing paths,
such that a path is a (sourceSTP, destSTP, SDPList).
I will need to have a look at this part of the document..
Best regards, Henrik
Henrik Thostrup Jensen <htj at
ndgf.org>
NORDUnet / Nordic Data Grid Facility.
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