Subject: Is the advertisement (IGP) of available BW at each pre-emption le vel is a DS-TE- requirement ?

From: "Choudhury, Sanjaya" <[email-masked]>
Date: Fri, 9 Nov 2001 14:30:12 -0500

Hi! I have few questions related to the LSP pre-emption in a DS-TE
	environment. I will appreciate, your help with these questions.

	Q1. If we support pre-emption _across_ different DiffServ classes,
	then what is the advantage in advertising available bandwidth for
each
	class at _each pre-emption level_ ?

	Q2. In general, does the advertisement of available of bandwidth
	at each pre-emption priority level, help in building/managing a 
	TE network ? 

	[Considering that at time t1 , there is might be enough BW for 
	class-x/priority-3, however at time t1+2min another LSP with	
	priority-2 might preempt the previous LSP.]

	Q3. In a DiffServ TE domain, where the network administrator
	initiates the creation the TE tunnels (using MPLS-TE-MIB ),
	when/how can he take advantage of the following pre-emption 
	scheme:
		a) Preemption within the same DiffServ traffic class 
		b) Preemption across different DiffServ traffic classes 

	Thanks,
	sanjay

---

From: Jim Boyle <[email-masked]>
Date: Fri, 9 Nov 2001 20:17:45 -0500 (EST)

> 	class at _each pre-emption level_ ?

There is no agreed upon protocol proposal for DS-TE right now, preemption
within and across class types is an issue that has been raised on the
list.  At this point, the requirements document is under a revision which
should clarify the need (or lack of need) for this, the revision is
expected in the next week (or so).  Francois or one of his co-authors
may answer your question more directly, as you are refering to their
proposal.

> 	at each pre-emption priority level, help in building/managing a

Yes.

> 		b) Preemption across different DiffServ traffic classes

I'm not sure how people use the MPLS-TE-MIB to setup TE tunnels, so I
can't help you there.  I think you mean class-type above, so again, that
is a specific proposal.

---

From: Francois Le Faucheur <[email-masked]>
Date: Tue, 13 Nov 2001 13:56:12 +0100

Choudhury,

>can't help you there.  I think you mean class-type above, so again, that

I am not sure I fully get the question (in particular I don't see the 
relationship with the fact that you set up tunnels using MIB or not), but 
let me quote some draft text from teh drafts we're working on as it may help:

"
First, a Service Provider using two Class-Types (one for Voice and one for 
Data), may elect to configure the following to ensure that Voice LSPs are 
never driven away from their shortest path because of Data LSPs:
         -all Voice LSPs to preemption priority 0
         -all Data LSPs to preemption priority 1

Another Service Provider may elect to configure the following in order to 
optimize global network resource utilization by favoring placement of large 
LSPs first:
-       all large size Voice LSPs to preemption priority 0
-       all large size Data LSPs to preemption priority 1
-       all small size Voice LSPs to preemption priority 2
-       all small size Data LSPs to preemption priority 3
"

Note that this is based on the observation that, today, a common use for 
preemption is to give higher preemption to large LSPs in order to get 
better global utilisation. You get a much better network utilisation by 
fitting big things first and then small ones (just like filling up the boot 
of the family car when going away on holidays, really).

Hope that helps.

Francois

> >       sanjay

_________________________________________________________
Francois Le Faucheur
Development Engineer, IOS Layer 3 Services
Cisco Systems
Office Phone:          +33 4 97 23 26 19
Mobile :               +33 6 89 108 159
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Email:                 [email-masked]
_________________________________________________________
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_________________________________________________________

---

From: Francois Le Faucheur <[email-masked]>
Date: Tue, 13 Nov 2001 14:05:52 +0100

Choudhury,

>may answer your question more directly, as you are refering to their

Our previous draft discussed the advantages of advertising bw at each 
preemption level for each Class-Type.
This includes :
         - ability to use one given preemption simultaneously by multiple CTs
         - no dependency on consistent configuration of CT/preemption mapping
         - easier migration scenarios

However, after discussing more with some Service Providers, it seems that 
smaller IGP advertisement maybe more important than these above 
benefits.  We are currently working on merging several of the earlier 
proposals into a common one which would advertise a total of 8 bandwidth 
values.

Francois