Subject: preemption in diffserv-aware TE

From: "Ju, Yu" <[email-masked]>
Date: Fri, 5 Oct 2001 16:26:00 -0400

Hi,

draft-lefaucheur-diff-te-proto-00.txt says "If a lower priority class (e.g.
AF) used some of the unused bandwidth of a higher priority class (e.g. EF),
the high priority class should be able to reclaim this bandwidth where
necessary  (i.e. preempt lower priority class - see section 2.5)". This
sounds to me that higher priority class type can always preempt lower
priority class as long as the higher priority class doesn't exceed its
percentage of link bandwidth. 

 However, the draft also says "Since preemption is defined independently of
Class-Types, the  solution supports multiple preemption priorities across
Class-Types.   To allow preemption among two LSPs of different CTs, the
network  administrator only need to configure the two LSPs with different  
preemption priorities."

So my question is: can a LSP with lower class type, higher preemption
priority preempt a LSP with higher class type, lower prermption priority?

Thanks,

Yu

---

From: "Don Fedyk" <[email-masked]>
Date: Fri, 5 Oct 2001 21:35:40 -0400

Hi Yu

> -----Original Message-----
> From: Ju, Yu [mailto:[email-masked]]
> Sent: Friday, October 05, 2001 4:26 PM
> To: [email-masked]'
> Subject: preemption in diffserv-aware TE
> 
> 
> Hi,
> 

> priority preempt a LSP with higher class type, lower 

The decision to preempt is not based on priority class. But the 
first decision is "Unused bandwidth in the AF class type is sufficient".
The second decision if this is satisfied is "the AF LSP being set up 
has a higher preemption priority than EF LSP. If both of these are 
satisfied then preemption can happen.

There are other drafts on preemption that don't allow this separation
in order to reduced flooded data. 

I always looks a Preemption priority as a connection priority that 
gives you a higher probability of getting and keeping your traffic.
It is not a guarantee, even without this class type bandwidth partition. 

Hope that helps,
Don