News to me
On Friday, September 11, 2026 at 05:42:10 AM PDT, Robert Raszuk
<[email protected]> wrote:
Hi John,
> Rather, I have consistently indicated my preference for the > provisioning
> system, since that is the entity which controls > the resources in a network.
My understanding is that no one is arguing that.
Best,R.
On Fri, Sep 11, 2026 at 2:34 PM John Drake <[email protected]> wrote:
Hi,
I have tried to avoid the term 'controller' because that term seems to have the
connotation of 'the entity which computes paths on behalf of other nodes' which
is NOT at all what I am talking about.
Rather what I am talking about is the entity that decides at every point in
time the set of links that can be used to carry traffic and the set of links
which can’t and which distributes this information to all of the nodes in the
network.
This is the entity which provides, as Robert blithely describes in one of his
earlier emails: "a hint flooded to headends to try to avoid the links which
are to be put to sleep".
I think this is a big job and one which can't be done in a distributed manner.
Rather, I have consistently indicated my preference for the provisioning
system, since that is the entity which controls the resources in a network.
As an aside, I am completely happy with distributed path computation.
Thanks,
John
On Friday, September 11, 2026 at 04:29:07 AM PDT, Barth, Colby
<[email protected]> wrote:
Robert,
Even a controller needs to sync topology state from the network and that may
take more time than normal IGP flooding.
-- Colby
From: Robert Raszuk <[email protected]>
Date: Friday, September 11, 2026 at 6:13 AM
To: Aijun Wang <[email protected]>
Cc: Barth, Colby <[email protected]>; Vishnu Pavan Beeram
<[email protected]>; John Drake <[email protected]>; John Drake
<[email protected]>; Tony Li <[email protected]>; WG TEAS <[email protected]>;
lsr <[email protected]>
Subject: Re: [Lsr] Re: [Teas] Re: Re: 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)
Hi Aijun,
Can we call such features as “undetermined ”?
Sure ... even with controllers in place nothing is 100% deterministic here.
Simply because you can only try to predict the future of your transit traffic
demands.
See controller will be doing the very same computation. However the difference
when using a controller - it will always have a full picture of the resources.
With distributed reoptimization you need to wait for your IGP reflooding or
RSVP-PATH failures to know that some capacity has been already "reserved" by
some other node.
So the way I look at this is that distributed CSPF and controller based may
eventually lead to pretty much the same final state .. it is just in the
controller case you will achieve it faster as it immediately has full view of
the entire network and its resources.
And, following your example, the challenge is, how to select the subset of
links that be put down, if many of their PCPPS are same?
You simply exclude all of them from CSPF and see during computation if what's
left still meets the TE policies. No great magic there.
Thx,R.
Aijun WangChina Telecom
On Sep 10, 2026, at 19:48, Robert Raszuk <[email protected]> wrote:
Hi Aijun,
The entire idea of distributed TE is no coordination between headends and it
still works.
Imagine a constraint - link failed in the core.
All headends see it and recomputre their LSPs such that the given link is not
considered in CSPF.
Here we are dealing with similar constraint ... ie. a hint flooded to headends
to try to avoid the links which are to be put to sleep.
Yes in both examples there will be contention for BW on the remaining links ...
yes in both cases RSVP PATH may fail to setup LSP, but this is how distributed
TE works since day one. That is btw why in TE we have quite a lot of control to
prioritize LSP between each other, we have preemption etc ...
But eventually LSPs get moved to those links in the topology which are not
going to be put to sleep. If there is no free capacity and if operator does not
agree to put a link to sleep even with some remaining LSPs still traversing it
the link will be kept up. Authors call it a feature and I will agree with them
on this.
Best,R.
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