Hi Igor, I think the client will still meet the case that there is no available path for the client.
The provider will have no chance to re-plan the path when the client knows the unfeasibility ahead of short time (e.g., milliseconds before it really needs the path) or the client knows the unfeasibility ahead of much time (e.g., hours or days) before it really needs, but there is no sufficient available resource for the provider to re-plan unless the operators add more physical nodes or links. I think the stateful path computation is a kind of “best effort”, and it might be suitable for IP service, but for the transport service, the protection capability(as you mentioned a failure recovery or congestion avoidance strategy or disaster topology re-configuration) MUST be guaranteed (at least for one single failure) if the client really relies on that. I think the simple way to guarantee the protection (or whatever) capability is to reserve the resource for the desired path and the reserved resource could be shared among multiple path (This is the concept of Shared Mesh Protection I introduced in ITU-T SG15 a few years ago, but here we can just reserve the resource from the control plane perspective rather than reserve the resource on the data plane through SMP mechanism). Thanks Fatai 发件人: Igor Bryskin 发送时间: 2016年11月9日 23:56 收件人: Francesco Lazzeri; Fatai Zhang; Dieter Beller 抄送: [email protected]; CCAMP ([email protected]); Scharf, Michael (Nokia - DE); [email protected]; TEAS WG ([email protected]) 主题: RE: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00 Francesco, Please, see in-line. Igor From: Teas [mailto:[email protected]] On Behalf Of Francesco Lazzeri Sent: Wednesday, November 09, 2016 10:27 AM To: Igor Bryskin; Fatai Zhang; Dieter Beller Cc: [email protected]<mailto:[email protected]>; CCAMP ([email protected]<mailto:[email protected]>); Scharf, Michael (Nokia - DE); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>) Subject: Re: [Teas] [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00 Igor, 1) IMHO simplicity pays back. Instead than maintaining all these states, notifying clients all the times something changes, and repeating path-computation as needed, isn’t better for a client (and provider) to ask what is needed when it’s needed, and get the best result back at that moment ? IB>> What happens it the provider at this moment says: “ No, I have nothing for you” ? What if the path was relied upon by the client for a failure recovery or congestion avoidance strategy or disaster topology re-configuration? FL>> Probably the same in case the provider notifies “Hey, I have no longer anything for you”. IB>> But this would be a bit too late, wouldn’t it? Wouldn’t it be better if the client has learnt about the previously returned path unfeasibility ahead of time, so that it could re-plan it’s failure recovery scheme? If there is no (more) path, there is no path. The client could only try and crankback looking for some different path or report an alarm. IB>> Relying on crankbaks in an unpredictable way is not exactly a good solution, right? The scenario that seems more applicable to your proposal is a pre-planned restoration mechanism where we have a worker path in-service and a protection path just computed (but not reserving network resources, in order to share them among several protection paths), in a multi-domain network. In that case, reserving te-tunnels like you suggest, could give an advantage, as the end-to-end cranckback could occur when the notification with “no-path” is triggered by the provider (that means the protection path or some of its segments is no longer valid) and not when the path deployment is triggered by the client (that means the worker path is gone and we need the protection immediately). Is this the case you are considering ? IB>> Exactly. All the scenarios you can think of where you don’t know when and where a problem may happen and you want to maintain flexibility and share the network resources to protect as much as you can In other cases, as when used during an end-to-end path computation with immediate deployment to reduce the possibility of conflicts among concurrent procedures, it seems to me less important or applicable, as all these procedures will likely be orchestrated by the same entity, which could well avoid conflicts. IB>> All cases where the provider wants to expose a potentiality without committing resources to cover for the client multiple use cases and provide at the same time some degree (albeit not perfect) predictability. 2) Regarding the abstract link in the overlay topology, I still can’t see what the provider will advertise. If it’s a new link representing the forwarding adjacency between A’ and B’, how it will be represented by the provider ? IB>> According to the TE topology model abstract TE link A’B’ points to the underlay (provider) TE topology where the path is computed and provisioned as supporting TE tunnel for committed TE link or not provisioned (but monitored) for uncommitted TE link (i.e. link advertising potentiality in the provider network). In either case TE link’s attributes (e.g. available bandwidth, SRLGs) are defined by the path. FL>> This means that the provider just sends the reply to the path computation request and doesn’t advertise any new TE link to the client ? This is actually what I would expect: the task to manage TE-links in the overlay topology is with the client. IB>> Overlay TE topology manager advertises a TE link that is supported not by a provisioned in a server layer TE tunnel (connection), rather, by a computed and monitored path. This way the overlay TE topology manger can advertise multiple abstract TE links mapped onto the same network resources Francesco From: Igor Bryskin [mailto:[email protected]] Sent: 09 November, 2016 3:47 PM To: Francesco Lazzeri <[email protected]<mailto:[email protected]>>; Fatai Zhang <[email protected]<mailto:[email protected]>>; Dieter Beller <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]>; CCAMP ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; Scharf, Michael (Nokia - DE) <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>> Subject: RE: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00 Francesco, 1) IMHO simplicity pays back. Instead than maintaining all these states, notifying clients all the times something changes, and repeating path-computation as needed, isn’t better for a client (and provider) to ask what is needed when it’s needed, and get the best result back at that moment ? IB>> What happens it the provider at this moment says: “ No, I have nothing for you” ? What if the path was relied upon by the client for a failure recovery or congestion avoidance strategy or disaster topology re-configuration? 2) Regarding the abstract link in the overlay topology, I still can’t see what the provider will advertise. If it’s a new link representing the forwarding adjacency between A’ and B’, how it will be represented by the provider ? IB>> According to the TE topology model abstract TE link A’B’ points to the underlay (provider) TE topology where the path is computed and provisioned as supporting TE tunnel for committed TE link or not provisioned (but monitored) for uncommitted TE link (i.e. link advertising potentiality in the provider network). In either case TE link’s attributes (e.g. available bandwidth, SRLGs) are defined by the path. Igor From: Francesco Lazzeri [mailto:[email protected]] Sent: Wednesday, November 09, 2016 9:26 AM To: Igor Bryskin; Fatai Zhang; Dieter Beller Cc: [email protected]<mailto:[email protected]>; CCAMP ([email protected]<mailto:[email protected]>); Scharf, Michael (Nokia - DE); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>) Subject: RE: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00 Igor, IMHO simplicity pays back. Instead than maintaining all these states, notifying clients all the times something changes, and repeating path-computation as needed, isn’t better for a client (and provider) to ask what is needed when it’s needed, and get the best result back at that moment ? Regarding the abstract link in the overlay topology, I still can’t see what the provider will advertise. If it’s a new link representing the forwarding adjacency between A’ and B’, how it will be represented by the provider ? BR Francesco From: Igor Bryskin [mailto:[email protected]] Sent: 09 November, 2016 2:48 PM To: Fatai Zhang <[email protected]<mailto:[email protected]>>; Francesco Lazzeri <[email protected]<mailto:[email protected]>>; Dieter Beller <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]>; CCAMP ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; Scharf, Michael (Nokia - DE) <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>> Subject: RE: [mpls] http://tools.ietf.org/html/draft-busibel-teas-yang-path-computation-00 Hi Francesco, Please, see in-line. Cheers, Igor The point here is for how long the provider should keep the computed path and its request parameters IB>> As far as the provider is concerned, the requested path and its parameters is a TE tunnel (albeit computed but not provisioned). So it keeps the state until the client removes the TE tunnel. (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. IB>> For example, if provider is to ensure the path’s feasibility, all it needs is to detect a change in a TE link the path is going through and make sure that the change does not make the path unfeasible. Only in the latter case the path re-computation needs to be scheduled and performed in a background thread. Furthermore, I can’t see how the provider could export the abstract TE-link, as this is inside the client topology; IB>> The abstract link is a part of the abstract topology “cooked” (customized) for the client, which is supported by the computed path in the underlay topology, which is the provider’s 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’. IB>> This is correct, but note that the two topologies (underlay and overlay) according to the TE topology model have independent and unrelated name spaces for node, link and SRLG IDs. So it is perfectly Ok. IB>> Also note that according to TE topology model one important attribute of a TE node (especially abstract composite node) is connectivity matrix, which is nothing but a set of stateful paths computed, re-computed and constantly monitored (but not reserved) over the TE topology the node encapsulates. This means that stateful unreserved paths play already a very important part in supporting TE topologies with asymmetrical blocking abstract TE nodes. Igor BR Francesco From: CCAMP [mailto:[email protected]] On Behalf Of Igor Bryskin Sent: 04 November, 2016 7:12 PM To: Dieter Beller <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]>; CCAMP ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; Scharf, Michael (Nokia - DE) <[email protected]<mailto:[email protected]>>; TEAS WG ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> 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:[email protected]] Sent: Friday, November 04, 2016 1:49 PM To: Igor Bryskin Cc: Leeyoung; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] Sent: Thursday, November 03, 2016 6:27 PM To: Leeyoung Cc: Igor Bryskin; Scharf, Michael (Nokia - DE); Daniele Ceccarelli; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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 <[email protected]><mailto:[email protected]> 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 ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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 ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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 ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] Sent: Thursday, November 03, 2016 3:17 PM To: Leeyoung; Daniele Ceccarelli; Igor Bryskin; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] Sent: Thursday, November 03, 2016 7:49 PM To: Scharf, Michael (Nokia - DE); Daniele Ceccarelli; Igor Bryskin; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] On Behalf Of Scharf, Michael (Nokia - DE) Sent: Thursday, November 03, 2016 8:58 AM To: Daniele Ceccarelli; Igor Bryskin; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] Sent: Thursday, November 03, 2016 2:49 PM To: Scharf, Michael (Nokia - DE); Igor Bryskin; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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:[email protected]] Sent: giovedì 3 novembre 2016 14:45 To: Igor Bryskin <[email protected]<mailto:[email protected]>>; Daniele Ceccarelli <[email protected]<mailto:[email protected]>>; CCAMP ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>) <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> 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:[email protected]] On Behalf Of Igor Bryskin Sent: Thursday, November 03, 2016 2:34 PM To: Daniele Ceccarelli; CCAMP ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]>; TEAS WG ([email protected]<mailto:[email protected]>); [email protected]<mailto:[email protected]> 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
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