[Nsi-wg] Immediate/Advance reservation (Re: NSI conf call minutes)

Artur Barczyk Artur.Barczyk at cern.ch
Tue Apr 13 03:10:34 CDT 2010 

Hi Inder,

I see, thanks for this clarification.

I still think we are introducing an artificial decision step here, which
will just be confusing to the end-user (and make the whole system
more complex), and I still wonder about the necessity of it.
Please see in-line:


On 04/12/2010 11:15 PM, Inder Monga wrote:
> Hi All,
> 
> I feel there is a lot of confusion, so let me try to explain my
> case/understanding. 
> 
> 1. Guard-time: 
> This concept was proposed for Advanced Scheduling only. This can be a
> default value and it does not have to be an "exact" measurement of
> provisioning times. It only handles path computation and reservation
> times across domains.
> 
> What does it mean to a user?
> A user CANNOT ask for a advanced reservation connection with Tstart <
> Tnow + Guard-time. If a user asks with a Tstart lower that Tnow +
> Guard-time, the scheduled request is rejected outright. 

Imagine I try to make a connection "NOW", and it gets refused after
N minutes due to lack of resources. Then I  try "2 minutes from now", and
it gets rejected straight off.
We shouldn't aim at having expert users who would understand this.
I think the system should behave in the same (and deterministic) way,
independent of what the user states in reservation time.
(Btw - that the reservation and provisioning time might vary does not
make it less deterministic.)

> 
> With an ADvanced Scheduling function, provisioning initiation can happen
> from both the user or the provider. 
> 
> 2. On-Demand Service: In my opinion, Guard-time does not prevent an
> On-Demand service as specified by Jerry. They co-exist. 
> An on-demand service, with Tstart = ASAP can be implemented very easily.
> The service starts when the "provisioning complete" message is received
> by the user. If the user does not receive that message, it continues to
> wait. 

Exactly what I was aiming at - but the same logic can apply to any time
between "NOW" and the guard time, or doesn't it?
All you need to do, if the start time is reached before the reservation
is complete, to wait for the latter.

> 
> Does this make more sense?
> 
> I will answer specifics below.
> 
[...]

>> What I meant is that if that time has passed by the time the provider
>> NSA gets notified of the reservation acceptance along the path, it
>> should proceed directly to provisioning.
> 
> In advanced reservation, the open question is what should a domain do if
> Tstart comes, and it has not got a reservation complete or provision
> message? Should it delete the connection or provision its own set of
> resources? Chin and I include this case in the error recovery document
> to be published soon.

No, no - simply wait for the reservation to complete. Only then will
you know if it succeeded in the first place.

IMO, the provisioning and reservation systems cannot be completely
decoupled. The provisioning stage should actually never be reached
until a reservation is complete. It is dependent on the outcome of the
path computation as well as resource reservation. Never go to provisioning
before you know you can have the resources.

> 
>>
>> You have to do this anyway, to protect against the guard time being
>> set too short. In which case you can just as well set the guard time to 0.
>>
>> That's just common sense, IMO, what it means when I would ask for
>> immediate
>> circuit provisioning. "Please give it to me as soon as you're able to,
>> I'm waiting."
>>
>> The thing not to forget is that someone can ask for a circuit not only
>> "now",
> 
> I think the "now" case is actually, "as soon as possible" - which is the
> on-demand case. Then it just waits for the right message from the
> Provider Agent before it knows the connection is available to be used. 

Yes, absolutely agree - that's a discussion terminology, which I'd be
happy to change :-)
However, we need to be precise on what we mean. An "ASAP" reservation,
from a user's point of view, could mean really "any time possible, starting
from now", i.e. also in 2 hours, if the resources will only then become
available.
I am not sure BoD does mean that.
Will in such a case a BoD reservation be converted into a scheduled one?

> 
>> but "a minute from now", which would lead to the same problem if the
>> time to
> 
> A minute from now actually becomes a "scheduled connection" and there is
> where the problem really starts. 

I am sorry I have missed large parts of this discussion, being kept off with
other workload. Sorry if I am coming back to things which might be obvious
to you by now.
But I do not really understand where the problem really is.
You mention the provisioning system to have to decide what to do
if  the reservation step is not complete - but I think the right design
decision
would be that the system should never actually be in such a state.
(Sorry, I am falling into thinking in terms of state machines here, but
well,
that's what I start to believe would be good here.)

Is there other reasons?

Cheers,
Artur

> 
> I feel we should support both Advanced Reservation with guard-time and
> On-demand connection service.
> 
> Inder
> 
>> process the reservation is longer than a minute (as it most probably
>> will be
>> in the next future).
>> So the "now" string as in your option 2) would only work for a singular
>> subset of the
>> problem.
>>
>> Cheers,
>> Artur
>>
>>
>>>
>>> Guy
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Artur Barczyk [mailto:Artur.Barczyk at cern.ch]
>>> Sent: 12 April 2010 17:28
>>> To: nsi-wg at ogf.org <mailto:nsi-wg at ogf.org>
>>> Subject: Re: [Nsi-wg] Immediate/Advance reservation (Re: NSI conf
>>> call minutes)
>>>
>>> Hi,
>>>
>>> I think guard time is a shaky concept, as who can tell how long it should
>>> be - it can/will depend on the number of domains the circuit
>>> contains, the
>>> speed of each reservation/provisioning system as well as the load on the
>>> system, and will be variable over time (hoping for faster
>>> reservation/provisioning
>>> systems in the future).
>>>
>>> But: if in step 5, the "wait for start time" means t_start <= t_current,
>>> then the
>>> provider will immediately pass on to provisioning.
>>> What needs to be done however is to have the duration of the reservation
>>> reflect the time difference between desired start time and the effective
>>> one.
>>>
>>> I am sure I am missing something..?
>>>
>>> Cheers,
>>> Artur
>>>
>>>
>>>
>>> On 04/12/2010 11:12 AM, Guy Roberts wrote:
>>>> Jeroen,
>>>>
>>>> Yes, that is correct.  But the mechanism will be the same for
>>>> advance reservations, just a later start time.
>>>>
>>>> Guy
>>>>
>>>> -----Original Message-----
>>>> From: Jeroen van der Ham [mailto:vdham at uva.nl]
>>>> Sent: 12 April 2010 08:19
>>>> To: Guy Roberts
>>>> Cc: John Vollbrecht; nsi-wg at ogf.org <mailto:nsi-wg at ogf.org>
>>>> Subject: Re: [Nsi-wg] Immediate/Advance reservation (Re: NSI conf
>>>> call minutes)
>>>>
>>>> To sum this up, this describes a situation where there is no prior
>>>> reservation and provisioning is started immediately because the
>>>> startTime is meant as a "now"?
>>>>
>>>> Jeroen.
>>>>
>>>>
>>>> On 09/04/2010 18:56, Guy Roberts wrote:
>>>>> John,
>>>>>
>>>>> My thinking of how it could work is as follows (though the details
>>>>> are really part of the protocol definition group's work):
>>>>>
>>>>> StartTime= time when the provisioning is begun.  This is the only
>>>>> possible meaning for StartTime since we have no way of knowing how
>>>>> long the provisioning will take in advance of the provisioning
>>>>> being performed. i.e provisioning completion time is
>>>>> non-deterministic.  For consistency as an asynchronous system, the
>>>>> completion of provisioning (in-service) is pushed by the NRM to the
>>>>> Provider which in turn sends this to the Requestor as a notification.
>>>>>
>>>>>
>>>>> Locally initiated provisioning:
>>>>> 1. The Requester NSA creates a request with a start time
>>>>> (StartTime).  StartTime= NSAs current time  + Requester guard time.
>>>>> Eg 12:00pm + 5 minutes = 12:05pm.
>>>>> 2. Provider validates the start time as being at least the provider
>>>>> guard time away from now. (note requester and provider guard times
>>>>> could be a little different to allow for transmission delay of request)
>>>>> 3. Provider begins the reservation process (12:01pm)
>>>>> 4. Provider completes the reservation (12:02pm)
>>>>> 5. Provider waits for the startTime (12:05pm)
>>>>> 6. Provider starts provisioning locally (12:05pm)
>>>>> 7. Provider waits for confirmation of provisioning from NRM (12:06pm)
>>>>> 8. Provider sends a notification to the requestor NSA to notify
>>>>> that the connection is in-service (12:06pm)
>>>>>
>>>>> Provisioning signalled by Requester:
>>>>> 1. The Requester NSA creates a request with a start time
>>>>> (StartTime).  StartTime= NSAs current time  + Requester guard time.
>>>>> Eg 12:00pm + 5 minutes = 12:05pm.
>>>>> 2. Provider validates the start time as being at least the provider
>>>>> guard time away from now. (note requester and provider guard times
>>>>> could be a little different to allow for transmission delay of request)
>>>>> 3. Provider begins the reservation process (12:01pm)
>>>>> 4. Provider completes the reservation (12:02pm)
>>>>> 5. Provider waits for the startTime (12:05pm)
>>>>> 6. Provider waits for the signal to provision (12:10pm)
>>>>> 7. Provider initiates provisioning of the Connection (12:10pm)
>>>>> 7. Provider waits for confirmation of provisioning from NRM (12:11pm)
>>>>> 8. Provider sends a notification to the requestor NSA to notify
>>>>> that the connection is in-service (12:11pm)
>>>>>
>>>>>
>>>>> Guy
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: John Vollbrecht [mailto:jrv at internet2.edu]
>>>>> Sent: 09 April 2010 17:28
>>>>> To: Guy Roberts
>>>>> Cc: John Vollbrecht; Tomohiro Kudoh; Jeroen van der Ham;
>>>>> nsi-wg at ogf.org <mailto:nsi-wg at ogf.org>
>>>>> Subject: Re: [Nsi-wg] Immediate/Advance reservation (Re: NSI conf
>>>>> call minutes)
>>>>>
>>>>> I am still a bit confused.  Perhaps someone could do a timing diagram  
>>>>> like the one Tomohiro did a while ago when we were discussing 2 phase  
>>>>> commits.
>>>>>
>>>>> I will try to explain my confusion.  My understanding has been that
>>>>> we  
>>>>> agreed that provisioning would never be done without prior  
>>>>> reservation.  So it would seem that the question being discussed is  
>>>>> "what is the time being requested in a reservation".  If the  
>>>>> reservation succeeds then provisioning can happen.
>>>>>
>>>>> It seems to me one question is how to define the start time being  
>>>>> requested.  The options seem to be that is is either 1) the time the  
>>>>> circuit is actually provisioned and ready to use or 2) the time that  
>>>>> provisioning of the circuit starts.  In one case the previous  
>>>>> connection may terminate sooner by the guard time and in the latter
>>>>> it  
>>>>> may start later by the guard time.    If it is (1) then a connection  
>>>>> scheduled for now must have been started at [now - (start time)].
>>>>>
>>>>> A second question is whether is is possible to request a connection  
>>>>> that starts "now".  This implies reserving a connection and
>>>>> initiating  
>>>>> it as soon as it is reserved.  Assume that start time is when  
>>>>> provisioning a circuit starts (case 2 above).  It seems that main  
>>>>> issue with this is whether the time to reserve a connection is longer  
>>>>> than the requestor is willing to wait.  The time it takes depends on  
>>>>> how many NSAs are "chained" to satisfy the request and how long each  
>>>>> NSA takes to reserve the connection.  This time is "authorization  
>>>>> time" not guard time as I understand it.
>>>>>
>>>>> There is another issue with defining authorization as "now" instead
>>>>> of  
>>>>> a specific time.  The problem is that each NSA in a chain will think  
>>>>> authorization happens at a slightly different time.  I am not sure
>>>>> how  
>>>>> important this is - it doesn't seem too important to me, but
>>>>> perhaps I  
>>>>> am wrong.  If provisioning starts after the reservation is complete,  
>>>>> then everything should be reserved, if at a slightly different time.
>>>>> ----------------------------------
>>>>>
>>>>> I think Guy is suggesting that start time is when provisioning starts  
>>>>> (case 2) above.  That seems simplest to me.
>>>>> I am not sure the provisioning time is important, and if not I would  
>>>>> think it good to include "immediate" reservation
>>>>>
>>>>> John
>>>>>
>>>>>
>>>>> On Apr 9, 2010, at 11:15 AM, Guy Roberts wrote:
>>>>>
>>>>>> Tomohiro,
>>>>>>
>>>>>>> In this case, only some parts of inter-network connection will be  
>>>>>>> provisioned.
>>>>>>
>>>>>> Right, I forgot about this reason - it is a good point.  Again, I  
>>>>>> think we are not complicating things too much if we have a rule that  
>>>>>> the Requester NSA cannot send a start time sooner than now+guardtime.
>>>>>>
>>>>>> I think we can solve the chain issue by not forcing any value for  
>>>>>> the guard time.  This can be a policy decision to suit the service  
>>>>>> type, equipment and number of networks involved.
>>>>>>
>>>>>> Guy
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Tomohiro Kudoh [mailto:t.kudoh at aist.go.jp]
>>>>>> Sent: 09 April 2010 09:04
>>>>>> To: Jeroen van der Ham
>>>>>> Cc: nsi-wg at ogf.org <mailto:nsi-wg at ogf.org>
>>>>>> Subject: Re: [Nsi-wg] Immediate/Advance reservation (Re: NSI conf  
>>>>>> call minutes)
>>>>>>
>>>>>> Hi Jeroen,
>>>>>>
>>>>>> There is a problem for inter-network connection. During the  
>>>>>> discussions
>>>>>> in some calls, the problem of synchronizing networks (managed by
>>>>>> different NSAs) was discussed.
>>>>>>
>>>>>> If you use the "now" type request for inter-network connection  
>>>>>> (without
>>>>>> complicated coordination), the actual provisioning time of networks  
>>>>>> may
>>>>>> be different. Moreover, some networks may provision resources before
>>>>>> some other networks reply to the request, and such networks might deny
>>>>>> the request. In this case, only some parts of inter-network connection
>>>>>> will be provisioned.
>>>>>>
>>>>>> The guard time is one of the simple solutions to solve this problem. I
>>>>>> understand there can be multiple ways to cope with this, but all of  
>>>>>> them
>>>>>> will introduce some complication to some part (note that we decided  
>>>>>> not
>>>>>> to use 2PC for the v1.0). This is a design choice matter.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Tomohiro
>>>>>>
>>>>>>
>>>>>> On Thu, 08 Apr 2010 09:27:59 +0200
>>>>>> Jeroen van der Ham <vdham at uva.nl <mailto:vdham at uva.nl>> wrote:
>>>>>>
>>>>>>> On 07/04/2010 15:02, Tomohiro Kudoh wrote:
>>>>>>>> If a requester wants resources to be provisioned as soon as  
>>>>>>>> possible, it
>>>>>>>> can set the start time parameter in a advance request to:
>>>>>>>> (current time + guard time + a certain time required for message
>>>>>>>> delivery).
>>>>>>>>
>>>>>>>> In this way, immediate provisioning can be requested by an advance
>>>>>>>> reservation request.
>>>>>>>
>>>>>>> The procedure above seems overly complicated and if I really am  
>>>>>>> pressed
>>>>>>> for time, and I miscalculate the (current time + guard time +  
>>>>>>> delivery
>>>>>>> time) by a few seconds. Denying the request means that I have to do  
>>>>>>> it
>>>>>>> all over again, making me even more pressed for time.
>>>>>>>
>>>>>>> Why not keep things simple and always interpret a start time in the  
>>>>>>> past
>>>>>>> as "now" ? (provided the end-time is in the future too)
>>>>>>> Would there be any problems associated with that?
>>>>>>>
>>>>>>> Jeroen.
>>>>>>
>>>>>>
>>>>>>
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>>>>>
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>>>>>
>>>>
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>>
>> -- 
>> Dr Artur Barczyk
>> California Institute of Technology
>> c/o CERN, 1211 Geneve 23, Switzerland
>> Tel:    +41 22 7675801
>> _______________________________________________
>> nsi-wg mailing list
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>> http://www.ogf.org/mailman/listinfo/nsi-wg
> 
> ---
> Inder Monga http://100gbs.lbl.gov
> imonga at es.net <mailto:imonga at es.net> http://www.es.net
> (510) 499 8065 (c)
> (510) 486 6531 (o)
> 

-- 
Dr Artur Barczyk
California Institute of Technology
c/o CERN, 1211 Geneve 23, Switzerland
Tel:    +41 22 7675801

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