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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
>
> >
> >