[Pce] 答复: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

[Fatai Zhang <[e-mail]>]

Hi all,

I share the same understanding as Dieter and Francesco.

I don’t see much value of the stateful path computation, because the computed path cannot be guaranteed and it brings much overhead as Francesco pointed.

I think it makes sense if the resource of the stateful path should be reserved (or allocatedButNotInUse used by Dieter).




Thanks

Fatai

发件人: CCAMP [mailto:[e-mail]] 代表 Francesco Lazzeri
发送时间: 2016年11月7日 16:50
收件人: Igor Bryskin; Dieter Beller
抄送: [e-mail]; CCAMP ([e-mail]); Scharf, Michael (Nokia - DE); [e-mail]; TEAS WG ([e-mail])
主题: Re: [CCAMP] [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00


The point here is for how long the provider should keep the computed path and its request parameters (in fact if we want to have a possibly better path, at any change inside provider topology, resource status and usage, the provider should check if the computed path is still feasible and/or redo path computation to find a better path). This could be an overhead, in my view.

Furthermore, I can’t see how the provider could export the abstract TE-link, as this is inside the client topology; in fact, if the client is asking for a path between A and B (A and B inside provider topology), having A’ (in client topology) connected to A and B’ (in client topology) connected to B, the relevant abstract TE link (the forwarding adjacency) should be built between A’ and B’, that is in the client topology; therefore the client should be in charge of managing it, as the provider is not aware of A’ and B’.

BR
Francesco

From: CCAMP [mailto:[e-mail]] On Behalf Of Igor Bryskin
Sent: 04 November, 2016 7:12 PM
To: Dieter Beller <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]>; CCAMP ([e-mail]<mailto:[e-mail]>) <[e-mail]<mailto:[e-mail]>>; Scharf, Michael (Nokia - DE) <[e-mail]<mailto:[e-mail]>>; TEAS WG ([e-mail]<mailto:[e-mail]>) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [CCAMP] [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Dieter,

A client may ask for a path not to be used immediately (e.g. to present as an abstract TE link to its own client, in some failure restoration scheme or as a part of disaster recovery network topology re-configuration) without committing any network resources. In this case the client would want to know at least  if/when the path has stopped being feasible any longer or (ideally) a better path is available.

This is similar to exposing to a client an abstract TE topology with an uncommitted abstract TE link (i.e. TE link that does not have a committed TE tunnel supporting it and advertises potentiality). Once such link is provided, the provider is expected to send updates when/if the TE link attributes change. For uncommitted/potential TE link such updates could be provided based on event driven re-computation of the potentiality the TE link represents.
The point is that an uncommitted abstract TE link and COMPUTE_ONLY TE tunnel can represent (each in its own way) the same network potentiality

Cheers,
Igor



From: Dieter Beller [mailto:[e-mail]]
Sent: Friday, November 04, 2016 1:49 PM
To: Igor Bryskin
Cc: Leeyoung; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: Re: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Hi Igor,

could you please clarify how useful a stateful path without resource allocation is. I can't see the benefits of this use case.


Thanks,
Dieter
On 04.11.2016 14:25, Igor Bryskin wrote:
Hi Dieter,

A provider may compute path(s) for a TE tunnel, and then (without any resource allocation) may start monitoring/ensuring the path validity/optimality by re-computing them in an event driven manner. For example, it can trigger the re-computation of the path(s) when detecting a change in a state of a TE link the current path(s) are going through.  Depending on the results additional notifications may be sent to the client.

Note that this is in addition to the reasons you correctly identified for implementing stateful path computation (such as compute_and_reserve).

Cheers,
Igor


From: Beller, Dieter (Nokia - DE) [mailto:[e-mail]]
Sent: Thursday, November 03, 2016 6:27 PM
To: Leeyoung
Cc: Igor Bryskin; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: Re: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00


Hi all,



when we talk about the stateful path computation use case, it means IMHO that when a path has been calculated successfully in response to a request, a new path object is created in the data store. This does only make sense if the resources have been allocated in the TED of the PCE irrespective of the fact whether the connection along this path will be established right away or at a later point in time. This will prevent further path computation requests from assuming that the resources are still available. As the TED of the PCE also has to reflect the network state, I would assume that the network resources can be in one of the following three states: available, allocatedButNotInUse,  allocatedAndInUse. The path objects also need state information reflecting for example the alarm state of the allocated resources. The path calculated earlier may become (temporarily) invalid due to a link failure affecting the path.



Does this make sense?





Thanks,

Dieter



Sent from my tablet



Leeyoung <[e-mail]><mailto:[e-mail]> wrote:


Igor,

When you say “state”, are you referring to the YANG datastore or some other “interim” state of those paths that are calculated but not instantiated as LSPs? If we were to update the YANG datastore for this, I would think that we may have some issue when the customer decided not to instantiate the TE tunnel (after the path compute request).

Thanks.
Young


From: Igor Bryskin
Sent: Thursday, November 03, 2016 3:02 PM
To: Leeyoung; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Young,

From the provider controller point of view COMPUTE_ONLY TE tunnels will have exactly the same state as “normal” (COMPUTE_ADN_PROVISION) TE tunnels.

Igor

From: Leeyoung
Sent: Thursday, November 03, 2016 3:42 PM
To: Igor Bryskin; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Igor,

In such case, would the YANG datastore be updated? I guess not. If not, then the system/controller has to keep this interim state, would it?

Thanks.
Young

From: Igor Bryskin
Sent: Thursday, November 03, 2016 2:34 PM
To: Scharf, Michael (Nokia - DE); Leeyoung; Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Michael,
You are exactly right. The purpose of the “compute-only” TE tunnel is to create/maintain the normal TE tunnel state and (re-)compute TE paths for the TE tunnel connections/LSPs but not signal/provision the LSPs.

Igor

From: Scharf, Michael (Nokia - DE) [mailto:[e-mail]]
Sent: Thursday, November 03, 2016 3:17 PM
To: Leeyoung; Daniele Ceccarelli; Igor Bryskin; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Isn’t the intention of defining "compute-only tunnels“ to create state in the controller, but not to signal them? If the tunnel should be signaled and resources shall be allocated, why not just configure a vanilla tunnel? Uses cases seem to exist for both variants, and both can be encoded in YANG. Is there anything I miss here?

Michael


From: Leeyoung [mailto:[e-mail]]
Sent: Thursday, November 03, 2016 7:49 PM
To: Scharf, Michael (Nokia - DE); Daniele Ceccarelli; Igor Bryskin; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Hi Michael,

I think I am with you on your point. If we use rpc, it is clear. On the other hand, if we were to use “stateful compute-only” it seems that the system/controller has to keep the state of the paths somewhere which is not YANG datastore. My understanding is that YANG datastore is updated only when the path is signaled and resource is allocated. Would this give the system/controller additional burden to keep the “interim” state?

Young

From: CCAMP [mailto:[e-mail]] On Behalf Of Scharf, Michael (Nokia - DE)
Sent: Thursday, November 03, 2016 8:58 AM
To: Daniele Ceccarelli; Igor Bryskin; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: Re: [CCAMP] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Maybe I miss something, but to me, the domain controller either computes a path stateless, which can be modeled in YANG in an RPC. Or the domain controller computes a path, stores state, and provides access to the result in the YANG datastore. In the latter case, whether resources are allocated, or whether the NEs get actually provisioned, is an orthogonal question.

As a side note, I am not sure of I would call a domain controller or an NMS a PCE. Path computation is only a subset of the functions of a domain controller.

Michael



From: Daniele Ceccarelli [mailto:[e-mail]]
Sent: Thursday, November 03, 2016 2:49 PM
To: Scharf, Michael (Nokia - DE); Igor Bryskin; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Can you please explain what the “stateful compute-only” stands for I don’t understand what is stateful in a path computation request only.
IMHO either I ask the PCE (SDN controller, NMS, whatever) to compute a path and then forget about it or I ask to compute and provision it. I don’t understand the value of asking for it and remembering about it.

BR
Daniele

From: Scharf, Michael (Nokia - DE) [mailto:[e-mail]]
Sent: giovedì 3 novembre 2016 14:45
To: Igor Bryskin <[e-mail]<mailto:[e-mail]>>; Daniele Ceccarelli <[e-mail]<mailto:[e-mail]>>; CCAMP ([e-mail]<mailto:[e-mail]>) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: RE: http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

We have discussed this before. From an implementer’s perspective, the two clean solutions to the problem seem to either stateful "compute-only“ tunnels or a stateless RPC.

Michael


From: mpls [mailto:[e-mail]] On Behalf Of Igor Bryskin
Sent: Thursday, November 03, 2016 2:34 PM
To: Daniele Ceccarelli; CCAMP ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>; TEAS WG ([e-mail]<mailto:[e-mail]>); [e-mail]<mailto:[e-mail]>
Subject: [ALU] [mpls]http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00

Hi,

From the draft:

6.    YANG Model for requesting Path Computation


   Work on extending the TE Tunnel YANG model to support the need to
   request path computation has recently started also in the context of
   the [TE-TUNNEL<https://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00#ref-TE-TUNNEL>] draft.

   It is possible to request path computation by configuring a
   "compute-only" TE tunnel and retrieving the computed path(s) in the
   LSP(s) Record-Route Object (RRO) list as described in [TE-TUNNEL<https://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00#ref-TE-TUNNEL>].

   This is a stateful solution since the state of each created
   "compute-only" TE tunnel needs to be maintained and updated, when
   underlying network conditions change.

   The need also for a stateless solution, based on an RPC, has been
   recognized.


   The YANG model to support stateless RPC is for further study.





IB>> Please, note, that in the TE Tunnel model we consider the COMPUTE_AND_FORGET mode. We also consider the concept of path computation action to be defined under the TE tunnel node. All this is to facilitate stateless path computations.

Cheers,
Igor