RE:

["Francois Le Faucheur (flefauch)" <flefauch@cisco.com>]

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 
>> 
>>