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RE:

Hi all,

At first, I would like to ask one question. 
Is there preemption across CTs in the MAM model ?

If there is preemption across CTs, there is aggregate limit implicitly in MAM with preemption.

In the Faucheur's example (link of 100 and BC0=50, BC1=50, BC2=50), when the link is congested, there are only CT0 and CT1 traffics.

in the first phase, there is only CT2 traffic with 50.
after that, there are requests of CT0 traffic demand with 40 and CT1 traffic demand 30.
if these requests are accepted, the link capacity is divided into CT0(40), CT1(30), CT3(30), because there is preemption across CTs.

However, if there is not preemption across CTs, there is aggregate limit in MAM with preepmtion(neither explicit nor implicit)

Regards,

Geunhyung

None of us is as smart as all of us
==========================================
Geunhyung Kim

E-mail: geunkim@postech.edu

Tel: +82-54-279-5655
Fax: +82-54-279-5699

Networking & Distributed Systems Lab.
CSE
POSTECH
===========================================

-----Original Message-----
From: owner-te-wg@ops.ietf.org [mailto:owner-te-wg@ops.ietf.org]On Behalf Of Francois Le Faucheur (flefauch)
Sent: Thursday, March 20, 2003 12:32 PM
To: Lai, Wai S (Waisum), ALABS; LE ROUX Jean-Louis FTRD/DAC/LAN
Cc: te-wg@ops.ietf.org
Subject: RE: 



Waisum,
As Jean-Louis said, there is no aggregate limit with MAM (neither explicit nor implicit).
If you have a link of 100 and BC0=50, BC1=50 and BC2=50, then you may very well endup with a load of up to 150 across the three CTs.
Hence, with MAM:
	- you may have preemption within a CT (ie an LSP of CTx may need to preempt another LSP of same CTx)
	- you will not have preemption across CTs (ie an LSP of CTx will not preempt another LSP of Cty, since those don't contend for bandwidth).
Cheers
Francois


>> -----Original Message-----
>> From: Lai, Wai S (Waisum), ALABS [mailto:wlai@att.com] 
>> Sent: 20 March 2003 04:13
>> To: LE ROUX Jean-Louis FTRD/DAC/LAN
>> Cc: te-wg@ops.ietf.org
>> Subject: RE: 
>> 
>> 
>> JL,
>>    Do you mean that there is no *explicit* constraint for 
>> the aggregate bandwidth reserved from different classes?  As 
>> I described in my previous reply below, when the constraints 
>> sum up to link capacity, there is "total isolation" with no 
>> preemption among classes (which is not necessary of course). 
>>  When this is not the case, then the link capacity will act 
>> implicitly as the aggregate constraint.  This is a natural 
>> aggregate constraint (or an appropriately scaled aggregate 
>> constraint in the case of overbooking) that does not need to 
>> be explicitly spelled out, right?  When this aggregate 
>> constraint is to be exceeded, then preemption among classes 
>> will act in accordance with the definition, which says that 
>> Reserved (CTb) <= BCb, i.e., the reserved bandwidth of a 
>> class is *either less than or equal to* the bandwidth 
>> constraint for the class, depending on the relative 
>> preemption priorities of the different classes involved.
>> Thanks, Wai Sum
>> 
>> -----Original Message-----
>> From: LE ROUX Jean-Louis FTRD/DAC/LAN
>> [mailto:jeanlouis.leroux@rd.francetelecom.com]
>> Sent: Wednesday, March 19, 2003 8:25 PM
>> To: Lai, Wai S (Waisum), ALABS
>> Cc: te-wg@ops.ietf.org
>> Subject: RE: 
>> 
>> 
>> Wai Sum,
>> 
>> Preemption among classes can definitively not occur with 
>> current MAM defintion, whatever the preemtion priorities, 
>> because there is no constraint for the aggregate bandwidth 
>> reserved from different classes
>> 
>> If you define BC2= 5M, BC1= 7M, BC0= 15M, then you can 
>> reserve simultaneously 5M of CT2 LSPs and 7M of CT1 LSP and 
>> 15M of CT0 LSPs.
>> 
>> To allow preemtion between classes you need constraint on 
>> the cumulated bandwidth reserved from diffrerent classes, 
>> which does not exist in MAM. 
>> 
>> 
>> Regards
>> 
>> JL
>> 
>> -----Message d'origine-----
>> De : Lai, Wai S (Waisum), ALABS [mailto:wlai@att.com]
>> Envoyé : mercredi 19 mars 2003 02:29
>> À : LE ROUX Jean-Louis FTRD/DAC/LAN
>> Cc : te-wg@ops.ietf.org
>> Objet : RE: 
>> 
>> 
>> Jean-Louis,
>>    Associated with each class-type (or simply referred to as 
>> a class in my draft, as stated in the 2nd paragraph of 
>> Section A.3) there is a preemption priority, which together 
>> form a TE-class.  This enables preemption among class-types.   
>>    "Total isolation between classes" is provided in MAM only 
>> when the bandwidth constraints for different classes add up 
>> exactly to the link capacity.  When this is not the case 
>> (e.g., with overbooking), there will be interference among 
>> classes.  As shown in my draft, the degree of this 
>> interference depends on the degree of bandwidth sharing, 
>> whether preemption is used or not, and the relative 
>> preemptin priority.  This is a general property for any BC 
>> models: the higher the degree of sharing, the less robust 
>> the service isolation.
>>    My view of overbooking is concerned with dimensioning a 
>> link to carry the different classes of traffic offered while 
>> meeting service objectives.  I have not explicitly used a 
>> multiplier to scale the bandwidth of might appear to be 
>> available and advertised, if that's what you are referring 
>> to.  But I think I have done that implicitly, so as to show 
>> the performance impacts, and the need for a judicious choice 
>> of overbooking multipliers.  Thus, my example of twice the 
>> normal traffic (while discussed in the context of overload) 
>> is effectively scaling with a factor of 2. 
>> Thanks, Wai Sum
>> 
>> -----Original Message-----
>> From: LE ROUX Jean-Louis FTRD/DAC/LAN 
>> >> [mailto:jeanlouis.leroux@rd.francetelecom.com]
>> Sent: Monday, 
>> 
>> March 17, 2003 8:59 PM
>> To: Lai, Wai S (Waisum), ALABS
>> Cc: te-wg@ops.ietf.org
>> Subject: 
>> 
>> 
>> Hi Wai Sum and all 
>> I have a question regarding draft-wlai-tewg-bcmodel-01 
>> Section A.3 : 
>> "Preemption is enabled so that, when necessary, class 1 can 
>> preempt class 2...." 
>> How can you apply this to MAM ??  
>> If I refer to 3.0 definition,MAM ensures total isolation 
>> between classes, preemption can occurs only inside a class, 
>> but not between classes
>> 
>> 
>> "Overbooking is allowed as it is to be described below..." 
>> How do you define overbooking here ? 
>> Overbooking is definitively not allowed in your RDM example (BC0=15) 
>> Regards 
>> JL 
>> 
>>