[Nsi-wg] Release command

[Jerry Sobieski]

Hi John -

I know a number of implementations that have not implemented the 
Modify() command - and probably won't either.   So lets remove it also. 
    If you really want to simplify the protocol and SMs, get rid of 
Modify.   :-)

but seriously...  Use cases and historical context:

Many connections will be in service over weeks, months or years. The 
idea is to be able to drop the circuit from its "in service" state 
without releasing the reserved resources back to the available pool and 
risk those resources being allocated to other Connections.   The 
potential for new reservations locking out or substantially changing the 
existing reservation was deemed unacceptable.   The circuit could be 
re-provisioned as long as it was still within the reservation window.

The use case would be for periodic maintenance where the circuit would 
be affected but where the interruption is expected and should not 
constitute an error.  Another use case can be where the reserved 
resources in one domain for a connection need to be modified (say a link 
is upgraded from 10 G to 100 G) - but the upstream or downstream domain 
resources should not be released back to the availability pool.   When 
the circuit data plane is broken there is no way to guaranty the privacy 
or security or reliability of user data - the Release enables the user 
to halt traffic and allow the circuit to be fiddled with....  The other 
domains should not generate alarms or otherwise act as if the connection 
is fully functional - but its not an error either.  Release is not just 
a cosmetic command.

I do not think there was an intention to modify the circuit as-built 
characteristics during a release - Indeed, I think the intent was to 
simply communicate to all NSAs in the tree that the data plane can be 
interupted without causing an "outage" or triggering alarms all up and 
down the path.     So while we probably did not document in sufficient 
detail what the user would experience as result of a release and 
re-provision, the sentiment was that the circuit would be "essentially" 
the same after reprovisioning.   (e.g. "The expected performance 
characteristics should be the same before and after a Release.")    I do 
recall the discussion where we stipulated that the data flow *should* be 
actively blocked during a Release since to admit user data without 
confirmation that all segments were in service would pose a security and 
reliability flaw to the performance guarantees.  However, I do not think 
anything about curtailing the flow at ingress made it into the spec.

A) Why is this difficult to implement?

B) To my recollection, the Release() was never considered an "optional" 
primitive in terms of implementation, just that it could be skipped in 
the life cycle protocol sequence thus allowing an active circuit to go 
directly to a Cancel state without passing through Released.  (This 
means only that the protocol can skip the Release action in cases where 
it is not needed - not that it is an optional primitive in an NSI CS 
implementation.)    So if it is not implemented I would consider it an 
incomplete implementation.

C) What behaviour are you thinking the Release is or is not doing? Or 
doing incorrectly?

This seems like a new proposal when we are trying to curtail any 
additional changes - particularly major changes which I think this is.   
I think we should retain the Release() primitive in its current form for 
v2.     WE can revisit the issue in v3 ?

just my thoughts..
Jerry


On 2/27/13 12:38 PM, John MacAuley wrote:
> Peoples,
>
> I understand the usefulness of having a release command from a networking perspective, but I know a number of implementations are not supporting it at the moment (and some have no intention of supporting it).  With my new "lets make the state machine as simple as possible attitude" I started to wonder what is the customer use case for this command?  Chin had one where someone wanted to keep their reservation, but wanted to free up bandwidth for others to use.  This is an interesting use case, but not the behaviour of the current command as documented.  Removal of this command can significantly simplify the protocol and state machine.
>
> Would it be possible for people to provide their customer use cases for this command?  I am wondering if it is truly needed, or perhaps, we have the incorrect behaviour defined.
>
> Thank you,
> John
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