Hi, Vishnu(and also Barth, Tony, or other experts who support such proposal)
We are arguing that, even in 100% TE environment, “Distributed Power-aware TE” is impossible, if the headend routers don’t exchange their path calculation results. Let’s make the analogy as “the WG document adoption call”-----each expert make the judgement based on his/her own knowledge. Even we exchange intensely our thoughts on the mail list, there are difficulties to make the consensus---how can you expect each headend can coordinate with each other, or, without coordinating with each other, to make the same decision, to put out of their own traffic out of one specific link? Some detail replies for your arguments are inline below. Best Regards Aijun Wang China Telecom From: [email protected] [mailto:[email protected]] On Behalf Of Vishnu Pavan Beeram Sent: Saturday, September 5, 2026 4:48 AM To: Robert Raszuk <[email protected]> Cc: Barth, Colby <[email protected]>; John Drake <[email protected]>; John Drake <[email protected]>; Aijun Wang <[email protected]>; Tony Li <[email protected]>; WG TEAS <[email protected]>; lsr <[email protected]> Subject: [Lsr] Re: [Teas] Re: Re: Re: Re: [Green] 【Distributed Power-aware TE is Impossilbe】RE: RV: Call for adoption: draft-many-teas-power-steering-01 (Ends 2026-09-10) {as a WG participant} The key issue here is not whether global centralized coordination is valuable — clearly it is — but whether it is the only viable way to achieve meaningful network-wide efficiency. The argument in favor of distributed TE is that it can still steer traffic in a globally useful direction without the operational cost and complexity of a centralized optimization loop. [WAJ] Each headend make the decisions themselves, How can you get the “globally useful direction”? please explain this conclusion in detail. I doubt there would be any dispute with the argument that global centralized coordination offers the best way to maximize network-wide efficiency. However, it is not the only viable model, and it is not always the operationally preferred one. In practice, many deployments already rely on the “most-fill” local path selection tie-breaker to bias TE path computation toward a preferred subset of links, and this knob is available across major vendor implementations. When such a tie-breaker is incorporated into a network-wide distributed TE profile, the resulting path placement, computed independently by different ingress nodes, is not arbitrary; it becomes intentionally polarized onto a narrower set of links. Over time, as tunnel bandwidth is resized and re-optimized, this polarization naturally converges toward the most efficient set of links, while leaving other links unused. [WAJ] “Such polarized effect” is your aim, but you don’t describe how to achieve it. This is key argument points. Would you elaborate it in more detail? The mechanism proposed in draft-many-teas-power-steering is conceptually no different. By carrying power-group information in the TED, distributed TE path computation gains the same kind of local biasing capability: ingress nodes can optimally place paths by taking power-group information into account, thereby consolidating traffic and increasing the number of links that may be eligible for power-sleep. In other words, the goal is not to compete with global coordination, but to make distributed TE path placement more effective overall without requiring a controller-based optimization loop for every case. [WAJ] If the aim can’t be achieved, we will not evaluate whether it is efficient or not. The key point is that path selection can be made “network-aware” — and this is where the IGP extensions come into play — even without full centralized coordination. The effect may be more gradual than a controller-based optimization, but it is still a real and effective mechanism for driving traffic onto a preferred subset of links and creating power-sleep opportunities in a scalable manner. [WAJ] Path selection can be made “network-aware”, but can’t achieve the “network-wide” effect. Because each headend determine the “network-aware” path itself. It will make the traffic oscillation, not concentrated. Regards, -Pavan On Fri, Sep 4, 2026 at 12:13 PM Robert Raszuk <[email protected] <mailto:[email protected]> > wrote: Hi Colby, I am not sure John is suggesting GCO. I think he as few other folks on this list are simply puzzled to how your proposal works in practice. I voice my questions few time - but did not get any clear answer. Namely my doubt comes down to the below question (maybe John and few others are also wondering about this too) Assume there is set of links and there are network resources which would have sufficient capacity to carry traffic from those links. Of course assume 100% TE. The question is how would you assume that few hundreds of headends will at their time to reoptimize LSPs act in concert that the same set of links is being dried out ? Well I have had a nice chat with Tony on the side and he revealed one subtle but vastly important point. The capability that given link can be put to sleep is not really a constant capability of that link. The same applies to Power Group. So such "capability" is advertised when some oracle thinks it makes sense. It is not described in ISIS draft like this. I guess all we are asking here is to learn if this advertisement (via IGP flooding) at specific time intervals of the network is what makes the hope that even 100s of headends will notice that and will start their own attempt to shift the traffic on links not painted as sleep capable. It may actually work at scale it is just that current version of the draft is not make it clear. Cheers, R. On Fri, Sep 4, 2026 at 6:03 PM Barth, Colby <[email protected] <mailto:[email protected]> > wrote: Hi John, I assume you’re making the case for Global Concurrent Optimization (once again)? Sure, that would provide better results than distributed TE. This is not a new argument, we already discussed it in this thread (and for many years, for that matter). As we’ve stated many times already, if you want a “Controller” to consume the power-group info (and all the associated per interface, per tunnel, power telemetry streaming) and perform GCO, this solution does not prohibit you. However, not all operators leverage a central Controller and GCO comes with its own ‘costs’ (also already highlighted in this thread by Tony) nor should we require it. Therefore, this proposal caters to both centralize and distributed TE to facilitate power savings. It would be nice if we could just discuss the specific IS-IS extensions we proposed and not continue this circular argument. Thanks, -- Colby From: John Drake <[email protected] <mailto:[email protected]> > Date: Friday, September 4, 2026 at 8:29 AM To: Barth, Colby <[email protected] <mailto:[email protected]> > Cc: John Drake <[email protected] <mailto:[email protected]> >; Aijun Wang <[email protected] <mailto:[email protected]> >; Tony Li <[email protected] <mailto:[email protected]> >; WG TEAS <[email protected] <mailto:[email protected]> >; lsr <[email protected] <mailto:[email protected]> > Subject: Re: [Lsr] Re: [Teas] Re: Re: [Green] 【Distributed Power-aware TE is Impossilbe】RE: RV: Call for adoption: draft-many-teas-power-steering-01 (Ends 2026-09-10) Colby, Your statement is incorrect. Because your proposal is distributed, there is always the possibility that links that should have been put to sleep are not, because the re-distribution of LSPs in order to put links to sleep is not co-ordinated in order to provide global co-ordination of that re-distribution. John Sent from my iPhone On Sep 4, 2026, at 11:07 AM, Barth, Colby <[email protected] <mailto:[email protected]> > wrote: John, It only results in no links being put to sleep IF there are insufficient resources to consolidate traffic. That’s a feature, not a limitation. -- Colby From: John Drake <[email protected] <mailto:[email protected]> > Date: Friday, September 4, 2026 at 7:14 AM To: Barth, Colby <[email protected] <mailto:[email protected]> > Cc: Aijun Wang <[email protected] <mailto:[email protected]> >; Tony Li <[email protected] <mailto:[email protected]> >; WG TEAS <[email protected] <mailto:[email protected]> >; lsr <[email protected] <mailto:[email protected]> > Subject: Re: [Teas] Re: [Lsr] Re: [Green] 【Distributed Power-aware TE is Impossilbe】RE: RV: Call for adoption: draft-many-teas-power-steering-01 (Ends 2026-09-10) Colby, Path placement in this proposal is indeed deterministic. However, its effects are not; i.e., even though it may be possible to put some links to sleep, this proposal will not do that deterministically. In particular, this proposal may not put any links to sleep. I don’t think that’s acceptable. John Sent from my iPhone On Sep 4, 2026, at 9:47 AM, Barth, Colby <[email protected] <mailto:[email protected]> > wrote: Aijin, Distributed TE path placement is deterministic. Tony’s example is about placing TE tunnels on paths with sufficient resources. You are criticizing many other solutions with your example. The PCE architecture follows the same model. -- Colby From: Aijun Wang <[email protected] <mailto:[email protected]> > Date: Thursday, September 3, 2026 at 6:23 PM To: 'Tony Li' <[email protected] <mailto:[email protected]> > Cc: 'TEAS WG' <[email protected] <mailto:[email protected]> >; 'lsr' <[email protected] <mailto:[email protected]> > Subject: [Teas] Re: [Lsr] Re: [Green] 【Distributed Power-aware TE is Impossilbe】RE: RV: Call for adoption: draft-many-teas-power-steering-01 (Ends 2026-09-10) Hi, Tony: Then, there will be no deterministic effect for the distributed power-aware TE, Right? Why the operator will deploy such proposal that has the unknown probability of success? And, for the power group related information, since they are static, and will almost never to be changed, even the controller based approaches need them, it is not the IGP's role to flooding them. Let's image the possible scenario: NMS configure the power group information on each device---->IGP flood such information among all the nodes---->BGP-LS collect such information to the Controller Why don’t we let the NMS synchronize such information to the Controller? In most of the real deployment, NMS is almost the same, or collocate with SDN controller. So, what's the usage of the distributed power-aware TE proposal? Best Regards Aijun Wang China Telecom -----Original Message----- From: [email protected] <mailto:[email protected]> [mailto:[email protected]] On Behalf Of Tony Li Sent: Friday, September 4, 2026 3:18 AM To: Aijun Wang <[email protected] <mailto:[email protected]> > Cc: TEAS WG <[email protected] <mailto:[email protected]> >; lsr <[email protected] <mailto:[email protected]> > Subject: [Lsr] Re: [Teas] [Green] 【Distributed Power-aware TE is Impossilbe】RE: RV: Call for adoption: draft-many-teas-power-steering-01 (Ends 2026-09-10) Hi Aijun, > Let's trim the discussions within TEAS only. No, let’s not. > "the relevant nodes can then detect that the link is idle and can put it into > power-sleep." via the "reserved bandwidth"? > Then the proposal depends solely on RSVP style TE. No. Other proposals are free to use the information as well. If you have a controller-based approach and want PSP information on the network, here’s one way. > Even so, how you assure all the ingress node will select to avoid the same > link along the e2e path that is determined by its own? Only behave in such > manner, can you move out of the traffic from one link step by step. There is no guarantee that all headends will be able to consolidate traffic. If the traffic levels are sufficiently low and the relevant headends compute paths that do consolidate traffic, then links can transition to power-sleep. If traffic levels are not sufficiently low and one headend cannot find a path that avoids the link, well, the the link cannot be put into power sleep. This is not a bug, this is a feature. > Changing the link metric can get the effect of " in the middle of a flock of > birds and clap your hands, they will fly away ". > But for the distributed TE proposal, the effect will be the birds fly from > east to west, and then from north to south, or, fly around within the forest, > because every edge router direct them to avoid some different tree. We are not changing the link metric. We are adding a penalty to the path for the link in question. There may be many links on a path that are capable of power-sleep, so there may be many penalties. Those penalties do not have to be the same from LSP to LSP, nor from head-end to head-end, nor from link to link to have an effect on path computation. As long as each headend finds a path with sufficient capacity, then the network is in an acceptable state. 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