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

[Francois Le Faucheur <flefauch@europe.cisco.com>]

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

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