RE: Question on DS-TE (solution) draft: How can I prevent preemption of a connection ?

["Iren, Sami" <Sami.Iren@marconi.com>]

Francois:
As much as I like the idea of having the capability
to prevent preemption, I am not clear about what
you are proposing. Furthermore, I am surprised that
you are seeing this as a problem now. I thought
from the draft it was very clear that we would loose
the ability to prevent preemption. The whole scheme
was based on that.
Anyways here are the points that I am not clear about:

* The draft states that each preemption priority is only
  used by a single CT. In this new proposal you are removing
  this restriction.
* Because of the above, we are loosing the ability to
  deduct the CT from the setup preemption priority of
  an LSP. Therefore, we need to signal CT as well as
  preemption priority for LSPs. Previously, we did not
  need to signal CT.
* What is the exact relation between CT and preemption priority?
  By assigning all the CTs to preemption priority 0 as
  in your example are we saying that no other preemption
  priorities will be allowed in the system?
  What are the changes required for this proposal in the
  signaling of LSPs?

In general I like the idea but I would like to get the 
details of the proposal.

Thanks,
--Sami

> -----Original Message-----
> From: Francois Le Faucheur [mailto:flefauch@europe.cisco.com]
> Sent: Wednesday, December 12, 2001 1:47 PM
> To: Choudhury, Sanjaya
> Cc: 'te-wg@ops.ietf.org'
> Subject: Re: Question on DS-TE (solution) draft: How can I prevent
> preemption of a connection ?
> 
> 
> Sanjay,
> 
> At 09:54 12/12/2001 -0500, Choudhury, Sanjaya wrote:
> 
> >         Hi! According to the latest DS-TE solution, the 
> signaled (setup)
> >         preemption priority is used to infer the bandwidth 
> constraint
> >         associated with a LSP.
> >
> >         By doing this, are we losing the ability to prevent 
> the preemption
> >         of a LSP (of a set of LSPs) , in a network using the DS-TE ?
> >
> >         [For example, an administrator may want to deploy 
> DS-TE in his
> >         network, but may not want (automatic) preemption of existing
> >         LSPs in response to the creation a new LSP.]
> >
> >         Thanks,
> >         sanjay
> >
> 
> I think you've raised a very valid point:
> As currently specified, the solution would not allow LSPs in 
> different CTs 
> to use the same preemption level.
> 
> I believe this can be fixed by making the solution a little 
> more flexible. 
> In essence what we would do is :
>          - consider that the 8 Bw values included in the IGP 
> advertisments 
> are no longer tied to preemption. The position of the Bw 
> value in the IGP 
> advertisement is considered purely as an index i,  0<=i<=7
>          - a mapping is defined on all the LSRs: i ---> 
> (preemption_level, CT)
>          - this mapping must be consistent throughout the DSTE domain
> 
> For example, I could use the above to ensure each CT has a differnet 
> preemption level (ie CT0 can preempt CT1, CT1 can preempt CT2) by 
> configuring the following mapping:
>          - BW value 0 is used for CT0/Preemption0
>          - BW value 1 is used for CT1/Preemption1
>          - BW value 2 is used for CT2/Preemption2
> 
> Alternatively, I could use the above to ensure all CTs have the same 
> preemption level by configuring the following mapping:
>          - BW value 0 is used for CT0/Preemption0
>          - BW value 1 is used for CT1/Preemption0
>          - BW value 2 is used for CT2/Preemption0
> 
> I had a chat with some of the co-authors about this and they 
> were fine with it.
> 
> Does that work for you too?
> 
> Thanks
> 
> Francois
> 
> >
> >
> >
> 
> 
>