Hi Inder-   I am not sure I agree with all of this...

Inder Monga wrote:

Radek

I agree with your statements;

 User is not interested in partial results, as he/she is not even aware/interested in which NSAs/domains are involved. User doesn’t care (if everything works fine ;) ).

The protocol should be designed with the user in mind. The user does not care about guard time values, differences in setup times for MPLS vs optical lambdas, and concern itself with choices an NSA/NRM will make in path-finding. 

The protocol designers can keep the user in mind, but the protocol is between the RA and the PA and and has a specific purpose: to reserve and instantiate a connection across the globe.  We need to keep in mind that the RA is not always the end user - it is by definition another NSA and could be an NSA in the tree/chain somewhere.  If we want to differentiate between the user and the network, then we can create a simplified User to Network API, and a different Network to Network API...but I don't think thats what we want to do (:-)   We need to IMO *not* think about the user, but to think about the Requesting Agent - regardless of who it represents.

Perhaps once the RA-PA protocol is tightly defined in all its nuances, we can develop/recommend an end user API that simplifies the the application's required interactions ??   This would allow an application to embed an RA in a runtime library/module and the application itself would only have to deal with the basic connection requirements....  just a thought.

In my opinion, 

a. the user should specify "Expected Start Time, Expected End Time". The NSAs/domains along the path determine resource availability and booking in their schedules based on their own configured guard time (guard times are not specified by NSI protocol. NSI connection service architecture should discuss them as a suggested concept).

While the guard times may be network specific, we do need to at least consider what we would like an NSA to do if for instance a provisioning guard time pushes a reservation forward into a previous reservation:   Do we  1) reject the request since we can't prepend our guard time and still make the Requested Start Time?   OR  2)  Do we retard the Estimated Start Time to allow for the guard time?   OR 3) do we reduce the guard time to fit the available lead time?

I think we now agree that the Start Time is just an estimate, due primarily to the guard time itself being just an estimate.  So none of these times are etched in stone...So which option do we recommend or require?   The protocol is sensitive to these various times - they cause timers to go off, messages to be sent, error handling to kick in...   If they are adjusted during scheduling or provisioning, we MUST understand what impact they will have to the protocol and how that will be carried through the service tree.

b. Within reasonable limits, the connection should be up as close to the start time as possible. The user can set his own policy/configuration on how long to wait after the start time to accept a connection. Since the resources are guaranteed, this is a connection of setup/provisioning only. Hence, there is no protocol state transition when start time is passed other than the messages that indicate the circuit is established end to end or teardown message initiated by the client.

Ah, but the rub here is that the "user" is an RA...but not all RAs are the end user.  We are defining the actions of an RA, regardless of whether it is a user NSA or an network NSA.  So we must insure that if the RA gets tired of waiting for provisioning to complete, that whatever actions it is allowed to take will be consistent and predictable through out the service tree for all the RA/PA interactions.    So the "user" actions are not irrelevant to the protocol.

c. We should not design a protocol that depends on time synchronization to work. In my opinion, the start time, expected time to provision aka guard time is best handled/shared as a SLA/Service definition issue.

I agree:  We cannot expect perfectly/exactly synchronized clocks anywhere in the network.  And therefore we cannot depend upon clock synchronization for any part of the protocol to work.   Which implies that the protocol must work when the clocks are NOT synchronized.   How do we insure this?   --> rigorous protocol analysis.

While the values of certain timers may be left to the Service Definition/SLA, as I state before, we must make sure that the protocol can function predictably and consistently in the face of all possible timing permutations that are possible among NSAs.  This rapidly gets very complex if we allow too many variables for the SD/SLA to define.  Sometimes, its ok to identify constants that the protocol must use so that we can validate the protocol and simplify implementation and deployment.  Indeed, often times when clocks are only slightly skewed they introduce race conditions that become more likely to occur requiring more careful consideration.

d. Similar semantics apply to the end-time as well.

Pretty much.  Across the board,  things like clock events, estimates, and service specific choices will create situations where we need to insure  the protocol and state machines will function properly across the full range of possible permuted values.   This is in general why protocol designers say "make it only as complex as it needs to be, and no more" - options breed complexity.

br
Jerry

_______________________________________________
nsi-wg mailing list
nsi-wg@ogf.org
http://www.ogf.org/mailman/listinfo/nsi-wg