RE: Preemption with MAM RE:

Waisum,
Let me try one more time.
Adding some implicit bandwidth constraint (or whatever you want to call that) is not a clarification to MAM. It is a different model. 
- Where MAM currently has a Maximum Number of Bandwidth Constraints of 8 (ie one per CT), this model would have a maximum of 9 BCs (ie one per CT plus one aggregate). BTW, this in turn, would require change to the ISIS/OSPF extensions which can only advertise 8 Bandwidth Constraints.
- You would have to add a completely new rule to the definition like:
	 SUM (Reserved (CTb) ) <= BC9, ( b in the range 0 <= b <= (MaxCT - 1))
- All the CAC formulas would be different
Francois


>> -----Original Message-----
>> From: Lai, Wai S (Waisum), ALABS [mailto:[email protected]] 
>> Sent: 25 March 2003 23:10
>> To: Francois Le Faucheur (flefauch); Geunhyung Kim; Dimitry 
>> Haskin; Te-Wg
>> Subject: RE: Preemption with MAM RE: 
>> 
>> 
>> Francois,
>>   Preemption across CTs in MAM was presented to the TEWG, at 
>> least as early as June 2002, when the 00 version of 
>> <draft-wlai-tewg-bcmodel> was submitted.  Dimitry's posting 
>> also confirmed this mode of operation.
>>   The MAM definition simply says that Reserved (CTb) <= BCb, 
>> i.e., the reserved bandwidth of a CT is *either less than or 
>> equal to* the bandwidth constraint for the CT.  Thus, when 
>> contention resulting in preemption across CTs occurs, the 
>> reserved bandwidth of a CT can/may be less than the 
>> bandwidth constraint for the CT, depending on the relative 
>> preemption priorities of the different CTs involved.
>>   We can add this clarification to the MAM spec.
>> Thanks, Wai Sum
>> 
>> -----Original Message-----
>> From: Francois Le Faucheur (flefauch) [mailto:[email protected]]
>> Sent: Monday, March 24, 2003 5:31 PM
>> To: Lai, Wai S (Waisum), ALABS; Geunhyung Kim; Te-Wg
>> Subject: Preemption with MAM RE: 
>> 
>> 
>> Waisum,
>> 
>> >> -----Original Message-----
>> >> From: Lai, Wai S (Waisum), ALABS [mailto:[email protected]] 
>> >> Sent: 24 March 2003 19:11
>> >> To: Geunhyung Kim; Te-Wg
>> >> Subject: RE: 
>> >> 
>> >> 
>> >> Geunhyung,
>> >>   Thanks for your query.  If preemption is disabled, then of 
>> >> course there will be no preemption, whether within a given 
>> >> CT, or across CTs, regardless of any BC model used.  
>> >> However, if preemption is enabled, then there can certainly 
>> >> be preemption across CTs in the MAM model.
>> >>   Francois, the DS-TE Requirements document does not place 
>> >> any restrictions on preemption in MAM.
>> 
>> That is correct.
>> 
>> >>   As stated in Section 4.4 of the DS-TE Requirements 
>> >> document, "if LSP1 contends with LSP2 for resources, LSP1 
>> >> may preempt LSP2 if LSP1 has a higher set-up preemption 
>> >> priority (i.e. lower numerical priority value) than LSP2's 
>> >> holding preemption priority regardless of LSP1's OA/CT and 
>> >> LSP2's OA/CT."  
>> 
>> That statement is correct. But note that it starts with " 
>> *IF* LSP1 contends with LSP2". With MAM as it has been 
>> defined for a long time in the TEWG, LSP1 can only be 
>> contending with LSP2 if they are in the same CT. If they are 
>> in different CT, they are each subject to independent 
>> bandwidth constraints and therefore simply can not be in a 
>> situation where they contend. So while preemption across CTs 
>> is not "forbidden", it is simply not applicable.
>> 
>> >>Different methods can be used to meet this 
>> >> requirement.  The MAM model takes care of it simply by an 
>> >> implicit aggregate constraint.
>> 
>> There is no such thing as "implicit constraint". There are 
>> Bandwidth Constraints which are all pretty explicit. The 
>> reason we've written down definitions for these models is so 
>> that everybody knows what are the bandwidth constraints.
>> 
>> MAM definition says:
>> "
>>            o Maximum Number of Bandwidth Constraints 
>> (MaxBC)= Maximum 
>>                Number of Class-Types (MaxCT) = 8 
>>              o for each value of b in the range 0 <= b <= 
>> (MaxCT - 1): 
>>                        Reserved (CTb) <= BCb, 
>> "
>> MAM involves just one Bandwidth Constraint per CT, and those 
>> are independent.
>> 
>> It may be that another model which has independent bandwidth 
>> constraint + aggregate constraint (this would basically be a 
>> hybrid between MAM and RDM) is a reasonable idea; but this 
>> is not MAM as it is currently defined.
>> 
>> Cheers
>> 
>> Francois
>> 
>> 
>> >>  Other models may use an 
>> >> explicit constraint.
>> >>   Geunhyung, your example below reflects the correct 
>> >> operation in MAM with preemption across CTs (assuming that 
>> >> CT0 has the highest set-up preemption priority, and CT3 is a 
>> >> typo of CT2).
>> >> Thanks, Wai Sum
>> >> 
>> >> -----Original Message-----
>> >> From: Geunhyung Kim [mailto:[email protected]]
>> >> Sent: Wednesday, March 19, 2003 11:57 PM
>> >> To: Te-Wg
>> >> Subject: 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: [email protected]
>> >> 
>> >> Tel: +82-54-279-5655
>> >> Fax: +82-54-279-5699
>> >> 
>> >> Networking & Distributed Systems Lab.
>> >> CSE
>> >> POSTECH
>> >> ===========================================
>> >> 
>> >> -----Original Message-----
>> >> From: [email protected] 
>> >> [mailto:[email protected]]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: [email protected]
>> >> 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:[email protected]] 
>> >> >> Sent: 20 March 2003 04:13
>> >> >> To: LE ROUX Jean-Louis FTRD/DAC/LAN
>> >> >> Cc: [email protected]
>> >> >> 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:[email protected]]
>> >> >> Sent: Wednesday, March 19, 2003 8:25 PM
>> >> >> To: Lai, Wai S (Waisum), ALABS
>> >> >> Cc: [email protected]
>> >> >> 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:[email protected]]
>> >> >> Envoyé : mercredi 19 mars 2003 02:29
>> >> >> À : LE ROUX Jean-Louis FTRD/DAC/LAN
>> >> >> Cc : [email protected]
>> >> >> 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:[email protected]]
>> >> >> Sent: Monday, 
>> >> >> 
>> >> >> March 17, 2003 8:59 PM
>> >> >> To: Lai, Wai S (Waisum), ALABS
>> >> >> Cc: [email protected]
>> >> >> 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 
>> >> >> 
>> >> >> 
>> >> 
>> >> 
>>