[Nsi-wg] time issue
John Vollbrecht
jrv at internet2.edu
Thu Sep 30 12:53:27 CDT 2010
Artur makes very clear why it is important to be able to predict starting available time and ending available time. Without it users won't come back.
I believe it is also clear that providers must schedule their resources in a way that includes setup and teardown time in addition to available time.
It is impossible to know exactly how long setup will take, so it is impossible to be absolutely sure exactly when a connection will be available. This is where SLAs come in. A provider who wants users to come back promises to have the connection available at a given time and pays a penalty for being late. If the penalty is big the provider estimates the startup time to be large. If the penalty is small it might reduce the startup time. So there is a concept of startup time that is needed prior to available time.
There are now 3 times - available time, resource time, and startup time. [teardown needs to be included as well, but I skip it for this example]
The relationships are straight forward: resource time == startup time + available time
Assume the requestor always asks for available time. Then
for automatic provision the provider schedules resource time, and initiates provisioning at start of resource time
To this point I think everyone agrees --
The main issue that is still of concern is -
for manual provision the provider schedules resource time (which is calculated from requested available time). For manual provisioning to provide the requested available time, the provider must return the setup time, either by returning the resource time as well as available time, or by including the (estimate) set up time.
The alternative is to have manual provisioning request resource time. In that case it seems to me it would be good to return (estimated) startup time so manual provisioning can be started at the time required to make the connection available. In this case the manual provision requests resource time, while the automatic provision requests available time.
---
A second issue that confuses discussion is the concept of "chained" segments. The issue is that if a number of segments are in a ete connection, each segment has its own, different, setup time. Somehow these need to be correlated to provide a setup time for the chain as a whole. This is a significant problem, but in my opinion is a problem for interacting NSAs, but is not something for the NSI to solve. We do need to have an idea of how NSA agents might solve this and be able to support their requirments in the protocol. It may be useful to define a "federating NSA agent" which uses NSI interface to exchange information. Such fedNSA agents have different requirements than NSA agents that coordinate applications with computing, networking, display and storage. Both use NSI.
---
I note that the concept of estimated setup time fits well with SLA, and with Artur's requirement to be confident of when a connection is available. It is something that a provider sells to a user (for cash or maybe just to keep him happy). I think we should include setup (and teardown) in the framework.
What do others think?
John
On Sep 30, 2010, at 1:02 PM, Guy Roberts wrote:
> Hi Artur,
>
> I guess you are making this request for a guaranteed start times with your ‘system-user’ hat on? On balance I agree with your proposal that connections should have a known start time, otherwise they are not useful to the user.
>
> The problem we are tackling here is that an unknown delay is inherent to the provisioning process– In particular I have experienced this with AutoBAHN. So the question is (as you say) to find a way of managing this in a deterministic way. Personally I agree with Radek, in that we don’t have enough system knowledge to be sure to remove these delays, so how do we handle this?
>
> My preferred solution would be that the requestor NSA always asks for "Available Time" (As per John’s definition), the onus should be on the provider NSA to begin this in advance to add some reliability to the system – if this is in fact achievable is not at all clear to me.
>
> Guy
>
> From: Artur Barczyk [mailto:Artur.Barczyk at cern.ch]
> Sent: 30 September 2010 16:25
> To: radek.krzywania at man.poznan.pl
> Cc: nsi-wg at ogf.org
> Subject: Re: [Nsi-wg] time issue
>
> Hi Radek, All,
>
> hmmmm, I for my part would be quite annoyed (to put it mildly), if I miss the first
> 15 minutes of todays HD conf call just because I reserved the resources a week
> in advance. "Around" has no place in a well defined protocol. No fuzzy logic, please :-)
> Consider also the "bored child in a car" scenario:
> RA: are we there yet? PA: no... RA: are we there yet? PA: nooo.... RA: are we there yet? PA: NO! etc.
>
> Be aware that users complaining are users quite quickly lost. You don't want that.
>
> So let's consider two example users:
> - high volume data transfers through a managed system: a data movement scheduler has
> reserved some bandwidth at a given time. This time comes, the application will just
> throw data on the network, it might use connection-less protocol, or not, but it will
> result in an error. It cannot wait "around" 15 minutes, as it will bring the transfer schedule
> in complete disorder. Such a "service" is just useless.
> - video conferencing/streaming. You reserve the network resource for 3pm because your
> meeting starts then. How do you explain to the video conference participant that the
> network prevented the conference to start for "around" 15 minutes? (Well, you can, but
> this will be the last time you'll see the user using your network :-) )
>
> In short, the only reasonable thing to do is to put the right mechanism in place to
> guarantee the service is up when the user requested it (and you confirmed it).
> The only acceptable reason for failing this is an error condition like network down (and we'll
> talk about protection in v2 :-) )
>
> I also think it is very dangerous to use "providing a service" as argument while the underlying
> protocols are not yet correctly specified. This is not theoretical, the service needs to be useful
> to the end-user, if you want some uptake. Fuzzy statements make it useless. The very reason people
> are interested in this is that it's deterministic - you know what you get and when. Otherwise use the
> routed network. :-)
>
> Cheers,
> Artur
>
>
>
> On 09/30/2010 03:37 PM, Radek Krzywania wrote:
> Hi,
> It’s getting hard to solve everything here, so let’s don’t try to solve everything here at once. So how about defining a start time as a best effort for v1? So we promise to deliver the service, yet we are unable to guarantee the exact start time in precision of seconds. If user want connection to be available at 2pm, it will be around that time, but we can’t guarantee when exactly (1:50, 2:01, 2:15). Let’s take a quite long time as a timeout (e.g. 20 minutes), and start booking the circuit in 5 or 10 minutes in advance (no discussion for v1, just best feeling guess) . The result will be that in most cases we will deliver the service at AROUND specified time. For v1 is enough, as we will be able to deliver a service, while in v2 we can discuss possible upgrades (unless our engineering approach discovers it’s fine enough :) ).
> For #1 – it may a problem for instant reservations. Here user want a circuit ASAP. We define ASAP as (see above approach) less than 20 minutes (typically 5-10 minutes probably, but that’s my guess), or not at all. Users may or may not complain on that. In the first case we are good. For the second case we will need to design an upgrade for v2.
>
> Synchronization IMHO is important, and out of scope at the same time. We can make an assumption that agents times are synchronized with precision of let say 10 seconds, which should be far enough. The agents will use system clocks, so they need to be synchronized at the end (NTP or whatever), but that not even implementation but deployment issue. So let put into specification: “NSI protocol requires time synchronization with precision not less than 10seconds”. If we discover it’s insufficient, let’s upgrade it for v2.
>
> We already have some features to implement, just to see if it works fine (works at all, actually). If user is booking a circuit a week in advance, I guess he will not mind if we set it up 15 minutes after start time (user IS aware of that as we specify this in the protocol description). We can’t however deliver the service shorter than user defined time. So we can agree (by voting, not discussing) the fixed time values. My proposal is as above:
> - 20 minutes for reservation as set up time
> - Service availability time (e.g. 13 h)
> - Service tear down time (it’s not important from user perspective, as since any segment of connection is removed, the service is not available any more, but let’s say 15 minutes)
> In that way, calendar booking needs to have reserve resources for 13h 35 minutes. IMHO we can agree on that by simply vote for v1 (doodle maybe), and collect more detailed requirements for v2 later on. I get the feeling we started quite theoretical discussion based on assumptions and guessing “what if”, instead of focusing on delivering any service (event with limited guarantee).
>
> Best regards
> Radek
> ________________________________________________________________________
> Radoslaw Krzywania Network Research and Development
> Poznan Supercomputing and
> radek.krzywania at man.poznan.pl Networking Center
> +48 61 850 25 26 http://www.man.poznan.pl
> ________________________________________________________________________
>
> From: nsi-wg-bounces at ogf.org [mailto:nsi-wg-bounces at ogf.org] On Behalf Of Jerry Sobieski
> Sent: Wednesday, September 29, 2010 9:33 PM
> To: Jeff W.Boote
> Cc: nsi-wg at ogf.org
> Subject: Re: [Nsi-wg] time issue
>
> Ok. I can buy this approach of #1. The Requested Start Time is immutable as the request goes down the tree (which disallows #2) - it is still a Requested Start Time, but NSAs are not allowed to change requested start time as the request goes down the tree. But you can't prevent #3 if thats what an NSA somewhere down the tree decides to do. The result would be a promise he may not be able to keep - but thats acceptable because the Estimated Start Time is just an estimate, its not binding.
>
> The point is, the local NSA cannot tell whether a remote NSA is using #1 or #3 since its totally up to the remote NSA to select the guard time appropriate for that request. Likewise, even if the remote NSA misses the Estimated Start Time, the requesting RA has no recourse other than to a) just wait until the provisioning completes or b) give up and release the connection. An SLA might influence the bad NSA to not low ball his provisioning guard time in the future, or it may provide a rebate for the jilted user, but these are not a protocol or a standards issue.
>
> This goes to John's comment on the call today about what happens inside the NSA between the PA role and the RA role... These actions are captured in "state routines" that are invoked when protocol events occur. These actions are generalized in the standard, but any heuristics like these approaches to guard time cannot always be mandated. In a protocol standard, what ever components are "required" or "must" items, must be verifiable in a conformance test. I.e. if someone comes up with an NSI imlementation, we should be able to put the reference implementation against the test implementation and we should be able to tell via protocol operation if the implementation under test is doing all the "must" items. If we say an NSA must use #1 above, there is no way to test it and confirm that it is doing so. If the test implementation uses #3, the only outward sign is that it may miss the start time on some connection(s), but it could have as easily just been a poor judgment call on the provisioning time - which is ok.
>
> So, in the standard, we can only recommend #1 be used. Or we can say the NSA "should" use #1. But we cannot require it.
>
> my $.02
> Jerry
>
> Jeff W.Boote wrote:
>
> On Sep 29, 2010, at 7:31 AM, Gigi Karmous-Edwards wrote:
>
>
>
> Jerry,
>
> For your question : " 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?"
>
> In my opinion, I think the answer here has to be # 1) each NSA must reject the request if their process to establish the connection requested can not meet the Start time. In my opinion an NSA should NOT be allowed to change the requested start time (this will cause all types of problems for other NSAs), so # 2) is not an option. The guard time for each NSA will most likely be vastly different and very dependent on the tools used by that network domain to configure the network elements for the requested path, so an individual guard time of an NSA is also nonnegotiable, so option # 3) is not an option.
>
> I agree #1 seems the most deterministic.
>
>
>
>
> I agree with Radek, ONLY Start times and End times should be used in the protocol and that guard times are only private functions of each individual NSA.
>
> I agree with this. The guard times are not additive across each NSA. The guard time from the perspective of the user will effectively be the maximum of each NSAa guard time in the chain. But, the user doesn't care as long as provisioning is accomplished by the users requested start time. That time would be in the protocol and would remain unchanged through each step of the chain. And, it shouldn't matter how long it takes to tear down the circuit either as long as the circuit is available until their requested end time.
>
> As to how to manage this time synchronization... I think it is totally reasonable to depend upon existing protocols. There are other protocols that already depend upon time synchronization, and many of them use NTP. We are not talking about needing very tight synchronization anyway. 1 second or even 10 seconds is plenty close enough. It is more about bounding that error.
>
> jeff
>
>
>
>
> Kind regards,
> Gigi
>
> On 9/29/10 8:45 AM, Jerry Sobieski wrote:
> 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
>
>
>
>
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> --
> Dr Artur Barczyk
> California Institute of Technology
> c/o CERN, 1211 Geneve 23, Switzerland
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