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RE: Question on DS-TE (solution) draft: How can I prevent preempt ion of a connection ?
Hi Francois! After you think through the problem (and
possible solutions), will it be possible for you to
post another revision of the DS-TE draft (including
the examples in Appendix) ? It will also be helpful,
if you can give us rough time frame for the next
rev.
Some more thoughts on the next rev. of DS-TE ...
1. It will be nice to include a section on the Preemption
in the context of DS-TE .
2. Where does holding priority fit in this scheme ? Is this
still a useful construct ?
3. TE-Class: Should the term be "Bandwidth Class/Pool" (
defined by a set of BW constraints & priority )?
4. Is the term ClassType (== identifies a set of bandwidth
constraint), redundant ?
Thanks,
sanjay
> -----Original Message-----
> From: Francois Le Faucheur [mailto:flefauch@europe.cisco.com]
> Sent: Thursday, December 13, 2001 10:06 AM
> To: Choudhury, Sanjaya
> Cc: 'Francois Le Faucheur'; 'te-wg@ops.ietf.org'
> Subject: RE: Question on DS-TE (solution) draft: How can I prevent
> preempt ion of a connection ?
>
>
> Sanjay,
>
> 13/12/2001 -0500, Choudhury, Sanjaya wrote:
>
> >Hi Francois!
> >
> > > -----Original Message-----
> > > From: Francois Le Faucheur [mailto:flefauch@europe.cisco.com]
> > > Sent: Wednesday, December 12, 2001 1:47 PM
> > > To: Choudhury, Sanjaya
> > > Cc: 'te-wg@ops.ietf.org'
> > > Subject: Re: Question on DS-TE (solution) draft: How can I prevent
> > > preemption of a connection ?
> > >
> > >
> > > Sanjay,
> > >
> > > At 09:54 12/12/2001 -0500, Choudhury, Sanjaya wrote:
> > >
> > > > Hi! According to the latest DS-TE solution, the
> > > signaled (setup)
> > > > preemption priority is used to infer the bandwidth
> > > constraint
> > > > associated with a LSP.
> > > >
> > > > By doing this, are we losing the ability to prevent
> > > the preemption
> > > > of a LSP (of a set of LSPs) , in a network
> using the DS-TE ?
> > > >
> > > > [For example, an administrator may want to deploy
> > > DS-TE in his
> > > > network, but may not want (automatic)
> preemption of existing
> > > > LSPs in response to the creation a new LSP.]
> > > >
> > > > Thanks,
> > > > sanjay
> > > >
> > >
> > > I think you've raised a very valid point:
> > > As currently specified, the solution would not allow LSPs in
> > > different CTs
> > > to use the same preemption level.
> > >
> > > I believe this can be fixed by making the solution a little
> > > more flexible.
> > > In essence what we would do is :
> > > - consider that the 8 Bw values included in the IGP
> > > advertisments
> > > are no longer tied to preemption. The position of the Bw
> > > value in the IGP
> > > advertisement is considered purely as an index i, 0<=i<=7
> > > - a mapping is defined on all the LSRs: i --->
> > > (preemption_level, CT)
> > > - this mapping must be consistent throughout the
> DSTE domain
> > >
> > > For example, I could use the above to ensure each CT has
> a differnet
> > > preemption level (ie CT0 can preempt CT1, CT1 can preempt CT2) by
> > > configuring the following mapping:
> > > - BW value 0 is used for CT0/Preemption0
> > > - BW value 1 is used for CT1/Preemption1
> > > - BW value 2 is used for CT2/Preemption2
> > >
> > > Alternatively, I could use the above to ensure all CTs
> have the same
> > > preemption level by configuring the following mapping:
> > > - BW value 0 is used for CT0/Preemption0
> > > - BW value 1 is used for CT1/Preemption0
> > > - BW value 2 is used for CT2/Preemption0
> > >
> > > I had a chat with some of the co-authors about this and they
> > > were fine with it.
> > >
> > > Does that work for you too?
> > >
> > > Thanks
> > >
> > > Francois
> > >
> > > >
> > > >
> > > >
> >
> > Can you explain the solution again ?
>
> will try. I haven't thought it through properly yet. Needs
> more thinking
> but seems doable.
>
> >
> > IGP:
> > 1. 8 available bw are advertised, using existing
> > constructs. ->Okay
>
> yep.
>
> > 2. How do I compute these ?
> > a) Based on setup priority
> > b) Based on setup priority + class
> type (/BC)
> > c) Based on class type(/BC)
>
> c).
> let's say that the i-th bandwidth value is mapped to CT c and
> preemption p.
> the i-th bandwidth value is computed to indicate the
> "available" bandwidth
> for the set of LSPs of preemtion p and CT c. It reflects the
> Bandwidth
> Constraint(s) associated with CT c and ignores all the LSPs
> of preemption >p.
>
> > CAC:
> > 1. How do I get the BW pool with which I need
> > to compare the requested BW with ?
> > a) From the setup priority ?
> > b) New signaled TLV ?
> > c) Combination of both ?
>
> This is open. I think either would work. We woudl need to
> evaluate them and
> pick one.
>
> > PCM:
> > 1. When I need to compute a PATH for a connection
> > what approach do I use ?
> > [Related to CAC]
>
> when you need to compute a path for an LSP, you woudl know
> the preemption
> of the LSP and the CT of the LSP. Using the mapping index
> <-->CT/preemption
> you know the index in Bw values. This tells ytou what
> available bw to
> consider on all the links.
>
> > Preemption:
> > 1. How do I determine which connection to preempt ?
> > a) Based on the standard setup/holding
> > priority ?
> > b) Based on a new signalled entity ?
> > c) combination of both ?
>
> through the mechanisms above you always know for every LSP both its
> preemption and CT.
> if an existing LSP has lower or equal numerical preemption
> value than the
> new one , you can preempt the existing one.
> If existing LSP has numerically higher preemption value, then you may
> preempt it. You woudl preempt it iff you are competing for
> its bw. This can
> happen if teh existing LSP is in teh same CT butr it can also
> happen if the
> LSP is inanther CT (eg. in the case where a given Bandwdith
> Constraint
> applies to more than one CT).
>
> > 2. How can I say don't preempt a specific
> connection ?
>
> The overal constraint is that the number of <CT/Preemption> pairs is
> limited to 8.
> (BTW , we are thinking of add a definition to call the
> <CT/preemption> pair
> something like TE-Class)
> Once you have selected 8 <CT/preemption> pairs, you can
> ensure that some
> LSPs don't preempt each other by using the same preemption
> level for those.
>
> Cheers
>
>
> Francois
>
> > Thanks,
> > sanjay
> >
> > >
> > >
>
>
>